The purpose of this study was to identify whether psychological stress increased as undergraduate dental students progressed through their studies from first to fifth year. Another objective was to determine if the perceived sources of stress have changed along the years.To achieve these aims, a cohort of students at the University of Jordan were followed from first to fifth year of dental school. Fifth year students completed both the General Health Questionnaire ‘GHQ-12’ which was used to assess psychological stress and the Dental Environment Stress questionnaire ‘DES’ which was used to examine the perceived sources of stress. The same cohort of students had completed similar questionnaires during their first year of study. Chi-square analysis and independent t-test analysis were performed to compare GHQ-12 and DES scores between first and fifth year.p = 0.05. Mean score for DES also increased between first and fifth year of study and the difference was statistically significant at p = 0.05.Results showed that psychological stress increased from first to fifth year of study. Eighty- nine percent of fifth year students scored over the cut-off point of three in the GHQ-12 compared to 58 % in the first year. The difference between the years was statistically significant at Results of this study demonstrated that stress in dental students at the University of Jordan increased along the years. Fifth year students showed a high level of psychological stress and methods to reduce that stress should be further investigated and utilized. Psychological stress among dental students has been a subject of interest for numerous investigators from around the world –18. PsycFindings from different studies have indicated that stress in dental students was quite high –15. WhenIn a recent systematic review of stress in dental students, it was recommended that more longitudinal investigations be carried out to assess whether stress in dental students actually increased as they advanced through their studies . In one The dental school at the University of Jordan offers a five year undergraduate course leading to the acquisition of a Doctor of Dental Surgery (DDS) degree. The first two years are preclinical in content and in the third year, students take an introductory course in clinical dentistry. Fourth and fifth years are clinical years and students are expected to examine and offer treatment to patients under supervision as part of their clinical training.Psychological stress in dental students at the University of Jordan was assessed in the year 2008 using the General Health Questionnaire (GHQ-12). Results of that cross-sectional study have demonstrated that stress was highest in fifth year students and lowest in first year students . The aimIn accordance with local legislations at The University of Jordan, ethical as well as scientific approval for the study were obtained from the scientific research committee at the Faculty of Dentistry as well as from the Deanship of Academic Research. Data collection took place at the beginning of the second semester of the academic year 2011/2012. Fifth year students enrolled at the Faculty of Dentistry, University of Jordan completed the study questionnaires. This was the same cohort of students that completed similar questionnaires in their first year of dental school during the academic year 2007–2008 . During Students were addressed at a lecture hall following a regular lecture and the purpose of the study was explained by the first author. Students were invited to take part in the study and ensured that participation was voluntary and anonymous. Consent was informed and implicit; if students proceeded to complete the questionnaires following the explanation, it was understood that they consented to participate. All students in attendance at the classroom completed the questionnaires except for one student who opted not to participate. Confidentiality was guaranteed since students were not asked to write their names or any other identifiers such as a university number on the submitted questionnaires.Participants were asked to answer three questionnaires in paper and pencil format and it took around 10 min to complete the questionnaires. The first questionnaire collected basic sociodemographic data. This included a question on gender, whether the first choice of university admission was medicine or dentistry, whether students entered university on competitive basis or not, whether they were living at home with their parents or not and whether their education was funded by their parents or not.The second questionnaire was the General Health Questionnaire ‘GHQ-12’, which was used to assess the psychological distress of students . GHQ-12 The third questionnaire was the Dental Environment Stress Questionnaire ‘DES’  which meData was entered into SPSS version 20 and analyzed. A missing value analysis was carried out and cases that had considerable missing information (>5 items) were excluded from the analysis. From fifth year data, one case (0.7 %) was excluded and three cases (4.1 %) were excluded from first year data. Following the exclusion of these cases, all variables in the three questionnaires were analyzed in order to calculate the percentage of missing values in each variable.The percentage of missing values was mostly low; less than 2.5 %, except for the following DES items: ‘amount of cheating at dental school’ 4.5 %, ‘financial resources’ 4 %, ‘lack of confidence of being a successful dentist’ 4 %, and ‘amount of assigned work’ 3 %. Since a missing data proportion of 5 % or less has been considered inconsequential , all varDescriptive analysis was carried out for the sociodemographic data. Independent t-test analysis was used to compare the two samples from first and fifth year with regards to sociodemographic variables, and no statistically significant differences were found. For the GHQ-12 as well as for the DES, mean, standard deviation and frequency distribution were calculated. The internal consistency of the GHQ-12 and DES was tested with Cronbach’s alpha test. Chi-square analysis and independent t-test analysis were performed to compare GHQ-12 results between first and fifth year and between genders. DES scores were compared between first and fifth year of study using independent t-test analysis. P-value was set at 0.05.In total, 67 fifth year students took part in the study, a response rate of 50 %. Following the elimination of one case for missing values, the number dropped to 66. Females constituted 76 % of fifth year sample while 24 % were males. Table The internal consistency  for the GHQ-12 was 0.77, while it was 0.86 for the 26 item DES questionnaire and 0.91 for the full 38 item DES questionnaire. These results indicated that agreement between items in the scales was acceptable, and pointed to the reliability of the scales.p < 0.0001). Regarding gender differences for fifth year sample, females had a higher mean GHQ-12 score than males which was statistically significant: .The GHQ-12 mean score using the 0–3 scoring method for students in their first year of studies was 1.2 with standard deviation ‘SD’ =0.5. During their fifth year of study, this cohort of students had a higher mean GHQ-12 score (1.8 with SD = 0.5). The difference between mean scores in first and fifth year was statistically significant . ‘Table X2 = 1.9, p > 0.05.Using the 0–0–1–1 scoring method for GHQ-12 with a cutoff point of more than three, the percentage of students in first year with evidence of psychological distress was 58 %. This increased to 89 % in fifth year, and the difference along the years was statistically significant  ‘Table During their first year of study, this cohort of students had a mean preclinical DES score of 2.2 (0.5). For fifth year students and in order to be able to compare the DES results with those collected during the first year of study; when students had no contact with patients, 12 items relating to clinical situations were omitted from the questionnaire. The mean score for the 26 item DES for fifth year students was 2.8 (SD 0.5). The difference in mean DES score between first and fifth years of study was statistically significant . The top five stressors from the 38 item DES questionnaire were: ‘completing clinical requirements’, ‘patients being late or not showing up for their appointments’, ‘full loaded day’, ‘examination and grades’, and ‘amount of assigned work’. The items are shown in Table . The topResults of the GHQ-12 indicate that stress level has increased with statistical significance between first and final years of study. This is in agreement with other studies that have investigated longitudinal stress in dental students , and witThis cohort of students is showing an excessively high level of stress, especially when compared with results from other parts of the world. A study that examined stress in undergraduate dental students from five European dental schools reported the average percentage of fifth year students scoring higher than the cutoff point of three on GHQ-12 was 44 % which is much lower than the percentage reported in this investigation . A previNumerous studies have found a statistically significant difference between genders on the level of stress observed in dental students , 11, 18,There was a statistically significant increase along the years in the mean score for the preclinical 26 item DES questionnaire. This was in agreement with other cross-sectional studies that have found that the highest DES score was reported by final year students , 11. In Results of the DES questionnaire might shed some light into what students regard as a cause of stress in the dental school setting. In this investigation, the top perceived sources of stress when considering the preclinical items changed a little between first and fifth years of study, although the mean score for each of the stressors increased. In their fifth year of study, the top stressor for this cohort of students was ‘a full loaded day’, whereas it was ‘examination and grades’ in their first year of dental school. During fifth year, students had multiple clinics and lab work that took up much more time than the mostly theoretical courses they had in their first year. Another item that appeared among the top five stressors for fifth year students was ‘late ending time’, when it was not a major concern for first year students. Having a full loaded day and a late ending time among the top perceived sources of stress showed that students had a lot of work to do in their fifth year of study and that this was taking up a considerable amount of their time.The above might offer partial explanation for the level of high stress that fifth year students expressed since they had little time for recreational activities that could help in relieving stress. Programs such as yoga, humor and reading have been shown to decrease stress among students in the health sciences . EncouraWhen considering the full clinical DES questionnaire the top perceived source of stress for fifth year students was ‘completing clinical requirements’. This item was also among the top perceived source of stress for fifth year students in previous examinations of stress in dental students at the University of Jordan , 9. WithTo help students cope with the stress of completing their undergraduate dental studies, a recent systematic review of stress management in dental students recommended the introduction of stress management programs as part of the dental curriculum, although the nature of such programs needed further investigation . ExampleStudents were asked to answer the questionnaires anonymously. Anonymity might have helped in getting true representation of how a student felt about items in the questionnaires but it was limiting in that it was not possible to follow up with the same student from first to fifth year. Students can differ in their inherent anxiety and ability to cope with stressful situations , therefoPsychological stress level increased as dental students progressed from first to fifth year of study. Fifth year dental students at the University of Jordan had a high level of stress when compared to results from other parts of the world. Programs to reduce that level of stress need to be further investigated and implemented.


The visual wulst of the zebra finch comprises at least two retinotopic maps of the contralateral eye. As yet, it is not known how much of the visual field is represented in the wulst neuronal maps, how the organization of the maps is related to the retinal architecture, and how information from the ipsilateral eye is involved in the activation of the wulst. Here, we have used autofluorescent flavoprotein imaging and classical anatomical methods to investigate such characteristics of the most posterior map of the multiple retinotopic representations. We found that the visual wulst can be activated by visual stimuli from a large part of the visual field of the contralateral eye. Horizontally, the visual field representation extended from -5° beyond the beak tip up to +125° laterally. Vertically, a small strip from -10° below to about +25° above the horizon activated the visual wulst. Although retinal ganglion cells had a much higher density around the fovea and along a strip extending from the fovea towards the beak tip, these areas were not overrepresented in the wulst map. The wulst area activated from the foveal region of the ipsilateral eye, overlapped substantially with the middle of the three contralaterally activated regions in the visual wulst, and partially with the other two. Visual wulst activity evoked by stimulation of the frontal visual field was stronger with contralateral than with binocular stimulation. This confirms earlier electrophysiological studies indicating an inhibitory influence of the activation of the ipsilateral eye on wulst activity elicited by stimulating the contralateral eye. The lack of a foveal overrepresentation suggests that identification of objects may not be the primary task of the zebra finch visual wulst. Instead, this brain area may be involved in the processing of visual information necessary for spatial orientation. In vertebrate brains, sensory information is often represented in an orderly manner. Our body surface is, for example, represented in the well-known homunculus in the somatosensory cortex . LikewisThe origin of the visual topographic maps within the brain is the retina. Its essential organization including photoreceptors, amacrine, horizontal, bipolar and retinal ganglion cells is similar in all vertebrates . It is aAs a rule, the dimensions of neuronal retinotopic maps depend on the density of retinal ganglion cells. The foveal area of many mammals, for example cats and primates ,10, has In mammals as well as in other vertebrates, it is not only one eye which is projecting to a given brain map. It has been frequently shown that information from both eyes is combined in retinotopic maps –13. In mThe visual system of birds consists of three parallel projections originating in the retina -tectofugThe aim of the present study is to investigate functional aspects of the telencephalic station of the thalamofugal pathway, the visual wulst, which receives information from the retina, relayed by several thalamic nuclei .).24]). IThe eyes of birds are, as mentioned before, in most aspects similar to those of mammals. Special features are the so called oil droplets which contribute to the high spectral sensitivity ,26, the The visual wulst receives visual input from the retina relayed by the optic thalamic nuclei. It consists of three roughly parallel oriented layers. Visual input from the thalamus reaches the middle layer, the IHA , and is transferred from this layer to the upper layer, HA  that sends projections back to the thalamus, and the lowest layer, HD  which is the source of intratelencephalic projections of the wulst . DevelopInformation from both eyes reaches the visual wulst in spite of the fact that, in contrast to mammals, the optic nerves cross completely to the contralateral side in birds. Pettigrew and Konishi  electropSuch binocular processing within the visual wulst, however, is probably a specialty of birds with frontally placed eyes and a quite large binocular visual field. Although there is a substantial amount of recrossing fibers, the influence of the ipsilateral eye on the activation of the wulst has been shown to be marginal in birds with laterally placed eyes like the chicken and the zebra finch –36. It hBased on our previous report on the existence of several retinotopic maps in the zebra finch visual wulst , we are 21 zebra finches of 100–110 days of age from the breeding stock of Bielefeld University were used for the imaging experiments. The retinae of additional three birds (age range 120–300 days) were used for the estimation of the ganglion cell density distribution and the measurements of retinal landmarks.All experimental procedures were performed according to the German Law on the Protection of Animals and permitted by the local government. All imaging experiments performed in Göttingen were approved by the „Niedersächsisches Landesamt für Verbraucherschutz und Lebensmittelsicherheit”(permission numbers 84–02.04.2011.A217 and 33.9-42502-04-14/1451), all retinal ganglion cells experiments by the "Landesamt für Natur-und Verbraucherschutz" .Procedures were performed as described previously . BrieflyNeuronal activity in the left visual wulst of zebra finches was captured using autofluorescent flavoprotein imaging ,39. For A high refresh rate monitor , covering 75°×50° of the visual field, was placed at various angles around the bird at a distance of 30 cm from the eyes. In the experiments examining the extent of the lateral visual field represented in the visual wulst, we used up to 5 different monitor positions in the horizontal plane : 0°  and compared these values by t-test with the combined two”foveal” monitor positions (30° and 60°). We did this because our first impression was that the 30° and 60° segments were bigger than the peripheral ones. Second, we used a Matlab routine to evaluate the number of pixels within the activated region having the same phase value, from every 10° of the visual field starting from -5° in the ipsilateral visual field to +95° in the contralateral visual field. 30° and 60° maps were chosen for this measurement as they very well covered the area around the foveal representation and also the periphery. Since there is substantial overlap between the two monitor positions, there are more measurements/cases for each segment in the overlap region. Again, all the pixels with an amplitude lower than at least 30% of the maximum responsive pixel were discarded.We used two parameters for the determination of evoked activity differences between bilateral and contralateral stimulation: magnitude of the neuronal activity and average amplitude of the activity. Magnitude of the neuronal activity has been explained above. In addition, we calculated the average amplitude of the wulst activation in the region of interest using ImageJ .For the inspection of retinal landmarks we used a method described in detail by Nalbach et al  who dete4, 2.2 ml 100% ethanol, 8.6 ml propylene glycol, brought to a final volume of 20 ml with dH2O), an anesthetic found to be ideal for birds  to obtain a two dimensional density map. The number of cells/mmNo attempt was made to correct the data for tissue shrinking or counting errors  as we wep<0.05; **: p<0.01; ***: p<0.001.One-way repeated measures ANOVA followed by Newman-Keuls multiple comparison tests was applied to compare the magnitude of activity of the retinotopic maps from the various monitor positions and to test foveal overrepresentation. Paired t-test was used to test the difference between the activity obtained using elevation and azimuth stimuli and also the difference between the activity evoked by the stimulation of contralateral eye and binocular stimulation. Values are expressed as mean±SEM. The levels of significance were set as *: Extending our previous study about wulst retinotopic maps , we hereWe used a vertical bar moving from left to right and from right to left (azimuth stimulus) to examine the fronto-lateral extent of the visual field represented in the visual wulst. Figs In all examined cases, there was a gradual shift in the location of the activated wulst region from anterior to posterior in the zebra finch brain when the visual stimulus was presented more laterally Figs  and 3. T2 = 0.4525, P = 0.0021) obtained from the various stimulus monitor positions. The strongest azimuth activity map was most of the time obtained when the stimulus monitor was at 60° (3.5±0.6) with respect to the eye . Yet again there was no difference between the area sizes  = 0.8216, p = 0.4677).Further comparison of the results from the different monitor positions revealed some interesting features of the intrinsic organization of the topographic representations. In mammals, as mentioned above, an overrepresentation of the foveal area has been found frequently. We therefore evaluated a potential foveal overrepresentation and also the interindividual variability of the maps between different birds by calculating the size of the areas between the azimuth lines of 10° distance along the topographic representation from -5° frontally to +95° along the horizon. 2 (black), surrounded by regions with slightly smaller densities of 16000 cells/mm2 (red), and 14000 cells/mm2 (orange). High densities were also found at a second spot "looking" more frontally in the visual field with a maximum of 16000 cells/mm2 . The fovea and the second dense area are connected by a strip of slightly lower cell density . This situation may be best described as a so-called visual streak [The density map illustrated in l streak . At the The retinal ganglion cell density map was then slightly rotated and enlarged without distorting it to adapt it to our landmark measurements. We located the fovea  or—60° , and azimuth Fig  and 9B oAfter having shown that visual stimuli positioned about 40 to50° laterally and -5-+25° vertically to the ipsilateral eye can activate the visual wulst, we next tested whether there is also a binocular wulst region activated from the frontal visual field, as present in mammals, and what effect binocular visual stimulation had on wulst activity. Six zebra finches were used for this experiment. The stimulus monitor was centered at 0°, in front of the beak. Both horizontal and vertical moving bars induced activity in approximately the same wulst location of the posterior map  and was laterally limited at +125°. Vertically, it reached from +25° above the horizon down to -10° below the horizon. By using eye aperture studies, Bischof  had deteAccording to our new imaging experiments, the vertical extent of the wulst visual field representation is rather small and corresponds to just a narrow strip along the horizon (-10 to +25°). This cannot be explained by measurement differences because the upper and lower limits of the avian visual field are much higher and lower than the limits measured here . Our expOne has to consider here that the visual wulst map is not the only brain region representing the visual field of the birds. It has been shown that the tectal map most likely represents the entire visual field ,54–56. SThe functions which have been attributed to the visual streak could also be the basis for an explanation of the visual wulst function if it was only the streak which is projecting to the visual wulst. This, however, is not the case. The visual field represented in the wulst map extends more dorsally than the streak and also reaches into the field lateral of the fovea. Thus, the enhanced density of ganglion cells along the horizon should, if the entire population of neurons was projecting to the visual wulst, result in a stronger representation within the retinotopic map. Especially, the fovea should show some overrepresentation. However, our wulst imaging experiments do not show this. According to our results, visual stimuli at 60°  as well as at 30° (roughly the second higher density region) indeed resulted in higher magnitudes of wulst activation which in turn may indicate that neurons within this area have a higher preference for the stimuli used in our experiments. But we did not observe indications of a spatial overrepresentation of foveal regions as it is present in the mammalian visual cortex. In macaque monkeys, the central 10% of the visual field are for example represented in 90% of the V1 area, in cats it is 50% , but theThe findings in cats (over- and underrepresentation) indicate that an increased density of retinal ganglion cells does not necessarily cause overrepresentation of this region in all brain areas involved in visual scene analyses. Most likely, each area is “just” accessing the information which is necessary to perform a certain task. V1 of mammals is thought to be involved in stimulus identification, and such a task needs a high spatial resolution as provided by foveal overrepresentation. Following this reasoning, the lack of a distinct foveal overrepresentation in the zebra finch visual wulst may indicate that foveal processing and stimulus identification are not the main tasks of the visual wulst.Given some preference for the fronto-foveal region, it rather appears that the wulst processes information from the visual field just along the horizon, and is not especially equipped for object identification which would most probably make use of the higher ganglion cell density within the fovea. We therefore speculate that approaching objects might be processed by the visual wulst. This is a testable hypothesis, and it fits well to a concept which has been raised some time ago by Watanabe and Bischof . On the The vertical limitation of the wulst visual field to a rather narrow stripe along the horizon is, however, not explained by this scenario. The same ideas which have been discussed above for an explanation of a visual streak may also apply here as well as the lesion based results concerning the visual wulst function . Both exAn interesting feature of the wulst posterior retinotopic maps is the higher magnification in the elevation compared to the azimuth direction: Ten degrees of visual space in the elevation direction were represented in a two to three times longer distance on the wulst compared to the azimuth direction. Such anisotropy of maps has also been found in a variety of mammals –72, but As mentioned above, the topographic maps within the mammalian visual cortex are partly receiving input from both eyes: within the so-called binocular segment, neurons respond to visual activation of both eyes. The extent of the binocular segment depends on the eye position of the animal. Mammals with laterally placed eyes and a small binocular overlap, i.e. a small frontal region where the visual fields of both eyes overlap, have a small binocular segment in their visual cortex compared with animals with more frontally positioned eyes with a larger binocular overlap. The basis of binocularity is a partial decussation of the optic nerves from both the eyes at the optic chiasm: in animals with a binocular zone, only ganglion cell axons from the nasal part of the retina cross to the contralateral hemisphere, whereas axons from temporal retina do not cross, but project ipsilaterally. The bigger the overlap of the visual field, the bigger is the binocular segment within the visual cortex. In contrast to mammals, in birds, the optic nerves cross completely to the contralateral side. Hence, ipsilateral stimulus processing and binocular interaction as shown in the visual cortex can be achieved only by a secondary re-crossing of fibers to the ipsilateral brain hemisphere. This actually occurs at both visual projections, the tectofugal ,74 and tOur results concerning the role of the ipsilateral input partly support the idea of such a suppression, but only for the "binocular segment" as discussed below. When stimuli were presented in the foveal region (60°), we observed a strong response from the contralateral eye—as expected. In contrast, stimulation of the ipsilateral eye elicited a much weaker and spatially much more restricted wulst activation . The facAs mentioned above, the idea of a repression of activation of one eye by that of the other applies for our experiments with frontal stimulation. In these experiments, wulst activity was considerably reduced Fig –10L whenSchmidt and Bischof  have dem


Despite attempts to improve diet at population level, people living in material and social deprivation continue to consume unhealthy diets. Executive function - the ability to regulate behaviour and resist impulses – is weaker in individuals living in deprivation. Dietary interventions that educate and persuade people to reflect on and actively change behaviour may therefore disproportionately benefit individuals who are socioeconomically advantaged and have stronger executive function, thus exacerbating inequalities in health resulting from unhealthy diets. In contrast, manipulating environmental cues, such as how far away a food is placed, does not appeal to reasoned action and is thought to operate largely outside of awareness to influence behaviour. People eat more of a food when it is placed closer to them, an effect seemingly robust to context, food quality and body-weight status. However, previous studies of this ‘proximity effect’ are limited by small samples consisting mainly of university staff or students, biased towards higher socio-economic position and therefore likely stronger executive function. This study aims to test the hypothesis that placing food further away from a person decreases intake of that food regardless of executive function.156 members of the general public, recruited from low and high socio-economic groups, will be randomised to one of two conditions varying in the proximity of a snack food relative to their position: 20 cm or 70 cm. Participants are told they will be taking part in a relaxation study – and are fully debriefed at the conclusion of the session. The primary outcome is the proportion of participants eating any amount of snack food and the secondary outcome is the mean amount eaten. Executive function is assessed using the Stroop task.The proposed study takes a novel step by investigating the effect of proximity on snack food intake in a general population sample consisting of those with high and low executive function, appropriately powered to detect the predicted proximity effect. If this effect occurs irrespective of executive function and socio-economic position, it may have potential to reduce inequalities patterned by socio-economic position if implemented in real-world settings such as shops or restaurants.ISRCTN46995850 on 07 October 2015.Registered with the ISRCTN registry: The online version of this article (doi:10.1186/s12889-016-3184-9) contains supplementary material, which is available to authorized users. The global burden of disease, including diabetes mellitus and various cancers, can be attributed in part to unhealthy diet . FurtherChoice architecture interventions to change health behaviour in micro-environments involve altering the properties and placement of objects or stimuli, such as food products . One wayEngineering aspects of the physical environment could be used to shape eating behaviour , 19. TheIn addition to testing the effect of food proximity on eating behaviour, the proposed study will also assess whether this effect is moderated by executive function.Executive function (EF) is an overarching term referring to a collection of top-down mental processes involved in behavioural control. These processes encompass inhibitory control of impulses, the flexibility to change mental states and updating memory of existing knowledge, each allowing us to monitor and control our behaviour –24. The People differ significantly in EF strength, reflecting differences in genetics  and earlThose in lower SEP groups are more likely to have unhealthy diets  and therConversely, interventions that involve altering environmental cues are thought to operate largely outside of awareness to shape behaviour and so are unlikely to activate reflective processes . TherefoMost intervention studies on the proximity effect have been conducted with highly educated samples of students or university staff. Even in studies involving participants who are more representative of the general population, these rarely explore the differential effects of an intervention by SEP  and few The proposed study is, to our knowledge, the first to recruit a general population sample to investigate moderation of the proximity effect by EF and SEP. Considering the finding that years living in poverty impacts negatively on EF  and EF sTo test the primary hypothesis that placing food further from a person decreases the likelihood that they take any food, and to test the secondary hypothesis that this effect is not moderated by EF.Consumption of a snack food is less likely when it is placed further from participantsThe proximity effect is not moderated by executive functionProximal snack: bowl placed 20 cm from participantDistal snack: bowl placed 70 cm from participantThe study is an experiment with a between-subjects design. Participants are randomly allocated to one of two proximity conditions:Study appointments are assigned to one of the two experimental conditions using a randomly generated number sequence. The external research agency recruiting participants is responsible for allocating participants to the appointments and is blind to the randomisation of participants to the conditions. Likewise, the research team is blind to, and have no control over, the process of allocating participants to the appointments.Participants are tested individually in an experimental session lasting approximately 45 min. The testing room measures 3.3 m by 3.9 m with a large table and chair; see Fig. http://rootsresearch.co.uk/). Participants are eligible for inclusion if they are aged 18 years and over, and are excluded if they have any relevant food allergies or intolerance. Participants are reimbursed £25 for their time.A research agency recruits participants from the general population via an online panel and the street (Based on the aggregate results of two previous studies  giving pDistance of the snack bowl from the participant is manipulated: 1) Proximal = 20 cm 2) Distal = 70 cm. The increase in distance from 20 cm to 70 cm has been found to significantly affect intake of snack food; with this effect not increasing in strength with distances beyond 70 cm .1000 g of chocolate M&Ms (without peanuts) is used, the same portion size used in a previous study testing the proximity effect experimentally . ChocolaCalculated from any difference in bowl weight from before to after the relaxation break.Calculated from the difference in bowl weight (g) from before to after the relaxation break.The primary measure of EF is a state measure of response inhibition using the Stroop Test, administered using Inquisit 4 software. Self-report measures are used for additional analysis: see Table 2 in the Additional file Assessed by the Stroop Test  which haThis calculation for interference has been used widely as a primary outcome of the Stroop test since the trials first conducted by Stroop .Assessed by WebEXEC, a 6-item self-report scale assessing the extent of problems individuals experience in every-day scenarios that involve executive functioning e.g. “Do you find it difficult to keep your attention on a particular task?” – see Table 2 in the Additional file Participants are not restricted from moving the bowl, which presents a potential issue whereby participants move the bowl and are then influenced by subsequent positions of the bowl rather than the initial position determined by the researcher as per protocol. This may affect the fidelity of the study. Any bowl distance manipulation by the participant is therefore recorded to enable assessment of the impact of moving the bowl on the effect of the proximity intervention.Assessed by education level  as a dichotomous variable, with participants obtaining up to 5 or more GCSEs/1 A-level classified as low SEP and those obtaining bachelor degree/diploma and above classified as high SEP.Assessed from ratings on a 100 unit visual analogue scale (VAS) to the statement “How pleasant would it be to experience a mouthful of chocolate now?”, anchored by “not at all” and “extremely” (adapted from ).Assessed using a 7-point rating scale anchored by 1 = “not at all” and 7 = “very” .Assessed using a five-item measure of perceived effort to access the snack food, rated on a 5-point rating scale anchored by 1 = “completely disagree” and 5 = “completely agree” .Assessed using a four-item measure of perceived salience of the snack food, completed on 5-point rating scales anchored by 1 = “completely disagree” and 5 = “completely agree” .Assessed using the four-item version of the Edinburgh Handedness Inventory  which asAs a cover story, participants are recruited on the basis that they are taking part in a study on relaxation and personality, in which snack food could be presented without suspicion . AwareneThe research agency recruits equal numbers of both low and high SEP participants based on education level in order to maximise chances of recruiting participants with high and low EF. On arrival to the session, participants are given the chance to read through the information sheet and complete a hard-copy of the consent form. Participants are asked to complete the Stroop, WebEXEC and delay-discounting measures on a laptop before being instructed to take a break for 10 min to relax.A bowl of M&Ms is placed on the table either at 20 cm or 70 cm from the right arm of the participant (depending on randomisation). A selection of four magazines  is placed at the same time as the bowl, in a constant position on the table in front of the participant. The following instruction is given: “Since this is a study on relaxation and personality measures, we would like you to take a break for 10 min. Feel free to look through the magazines and help yourself to the M&Ms; I will be back in 10 min”. The researcher removes the laptop and leaves the room for 10 min. Upon re-entering the room the researcher removes the bowl of M&Ms and magazines. The bowl is then weighed and stored out of sight of the participant. Participants are asked to repeat EF measures to give credence to the cover story before completing the questionnaires. Questions pertaining to snack food are administered after participants are asked about their awareness of the intervention to prevent suspicion of the nature of the study earlier in the procedure. Participants are then debriefed and reimbursed for their time. See Table 2 in the Additional file Hypothesis 1. Consumption of a snack food is more likely when it is placed nearer to participantsA Hurdle model is a two-part model in which the first stage models probability of participants taking any snacks (yes/no = binary) and the second stage models the amount of snacks eaten for participants who took any snacks (measured in grams = continuous). For the first stage, a logistic regression is conducted to investigate any between-group differences by condition in the primary outcome - the proportion of participants eating any snacks (%). In the second stage of the model, a General Linear Model (GLM) is used to assess between-group differences by condition in the secondary outcome – the mean intake of snacks (g). Effects of the intervention on the secondary outcome are examined for both the sub-sample of participants who take any amount of snacks (i.e. excluding those who do not take any snacks) and additionally for the full sample (thus including those who do not take any snacks).Hypothesis 2. The proximity effect is not moderated by executive functionInterference score is entered into the analysis as the primary measure of EF. A logistic regression is conducted with proportion of participants taking snacks as the outcome and proximity as the predictor. An interaction term for proximity and EF is included in the analysis to investigate whether EF moderates the proximity effect.Analyses conducted to test the two study hypotheses are as follows:A similar procedure is used to examine WebEXEC and delay discounting measures as additional indices of EF.The dichotomous SEP variable is entered into the analysis as the primary measure of SEP. Logistic regression analysis is conducted with proportion of participants taking snacks as the outcome and proximity as the predictor. An interaction terms is included for proximity and SEP to investigate whether SEP moderates the proximity effect.Independent t-tests are conducted to analyse whether mean ratings of perceived effort and salience differ by proximity condition; alternatively, Mann–Whitney U tests are conducted if assumptions of normality are not met. A logistic regression model is conducted including perceived effort and salience of the M&Ms, with proportion of participants taking snacks as the outcome and proximity as the predictor, to investigate whether these variables affect the primary outcome. Further analyses includes exploration of the potential mediation of perceived effort and perceived salience on any observed main effects of proximity intervention on the proportion of participants taking any snacks.Liking for chocolate has been found to affect intake of chocolate M&Ms  and is tBecause participants are not restricted from moving the bowl, this presents a potential issue whereby participants move the bowl and are then influenced by subsequent positions of the bowl rather than the initial position determined by the researcher as per protocol. We intend firstly to examine the effect of proximity using an intention-to-treat approach, whereby participants are analysed according to the condition to which they are randomly assigned. However, should we find that participants do indeed move the bowl, we will conduct additional per-protocol analysis, including only participants who adhere to the protocol as intended i.e. where the position of the bowl as determined by the researcher remains unchanged throughout the experimental session.The proposed study adds to the literature in two ways: 1. by investigating the effect of proximity on snack food intake in a larger general population sample consisting of both high and low SEP participants, appropriately powered to detect the predicted proximity effect, and 2. by estimating the extent to which the proximity effect is moderated by EF.Previous studies investigating the proximity effect may have generated results that are not generalisable to general populations given investigators have tended to either purposefully recruit university staff and students , 15, 36 Previous experimental studies investigating proximity are also often limited by small sample sizes, reducing the reliability of the results. Studies have tested as few as 12 or 17 participants in each condition , 14, 15,The proposed study is, to our knowledge, the first to estimate the extent to which the proximity effect is moderated by EF. This study is powered on the primary outcome corresponding to Hypothesis 1 and is not powered to detect an interaction between EF and proximity in order to support or undermine Hypothesis 2.According to a provisional power analysis based on limited available data, very large samples are required to detect such an interaction, which is unfeasible for this study. As such, whilst this study may detect an interaction, which is contrary to Hypothesis 2; if it does not detect an interaction, this does not necessarily confirm Hypothesis 2 . However, this study should provide the best available data to inform powering of future studies, building a foundation towards a stronger and more solid evidence base to inform Hypothesis 2.If results are consistent with Hypothesis 2, the proximity effect should be present regardless of individual differences in EF. A similar effect of proximity on snack intake in both high and low EF participants would be compatible with the explanation that the proximity effect operates outside of the influence of EF. This suggests that proximity would be an effective intervention to alter selection and consumption of food with the potential to reduce SEP patterned behaviours such as poor diet that contribute to health inequalities.This study provides the first attempt to estimate the effect size of the proximity effect on consumption across social groups i.e. those from low as well as high SEP groups, and in relation to a potential cognitive moderator of this effect, namely executive function. Manipulating proximity, like other components of choice architecture, should ultimately be tested for its effectiveness to bring about sustained changes in dietary behaviour . TherefoEF, Executive function; RIM, Reflective-Impulsive Model; SEP, Socio-economic position; VAS, Visual analogue scale.


Therefore, the smallest parcel that can be productively used was considered as 5000 m2. On the basis of the analysis of the data pertaining to the easement rights having two different widths and collected from three different regions having different parcel sizes, the research aims to find out the number of parcels with an area less than 5000 m2 (excluding the easement) that were created by the construction of pipelines and to investigate whether a significant number of areas less than 5000 m2 remain. This study also demonstrates a method that can be used in studies on this subject according to the various parcel sizes that were created by the allotment of parcels due to the easement of the construction of pipelines.This paper examines whether the parcelization of land through easement as a result of the construction of pipelines in rural areas in Turkey has any negative effects on productive land use. The current legislation in Turkey does not allow the division of land in most rural areas into parcels smaller than 5000 m A pipeline is one of the most effective methods for transmitting energy sources like petroleum and gas  technologies are another process used for determining the pipeline routing. Reducing construction costs, as well as potential environmental damages, and minimizing construction period of pipeline projects depends on appropriate route planning at the beginning of the process. With this aim, all factors which will have an impact on the route should be examined and analyzed in an integral manner. Depending on the distance between reserve and target destinations, frequent changes are observed in the surface  and underground  characteristics, which result in a dense data set. Efficient management of this data and obtaining accurate results can be possible by using GIS technologies based on Raster Data Models  Each parcel that will be obtained after the allotment to be made outside of the residential area that has not upper scale plan cannot be smaller than 5000 mThe Zoning Law regulates the conditions of the settlements and housing in these areas in accordance with the zoning plan as well as the requirements of protecting environment and health. Article 62 of the Unplanned Areas Zoning Regulation enacted on the basis of this law reads as follows . Secondly, the sum of the remaining area out of use and permanent easement area was found . Finally, the difference with the total affected area and the permanent easement area were examined by using statistical tests. The statistical analysis rests on the parcel sizes registered in the land book.Firstly, the sum of the remaining area on the left and/or on the right less than 5000 mIn this study, statistical information was obtained by using the IBM SPSS Statistics 21 program.2, of the remaining areas less than 5000 m2, of the deed area ratio of the permanent easement area, of the deed area ratio of the total affected area along the pipeline and of the difference between the total affected area and the permanent easement area were shown. Descriptive statistics calculated are shown in Table First, descriptive statistics of the parcels, of the permanent easement areas, of the sum of permanent easement areas and remaining areas less than 5000 mSome of the variables in Tables The Permanent Easement Area/Deed Area Ratio: This ratio is calculated by dividing the permanent easement area size by the area size of the plot as registered in the title deed.The Total Affected Area/Deed Area Ratio: This ratio is calculated by dividing the total affected area size by the area size of the plot as registered in the title deed.Determination of level of significance α = 0.05 (type I error)Determination of test power β = 0.95 (type II error)The smallest sample size n  in the shortest pipeline is equal to 962 , sample size was calculated using the formula given below  < 0.05 (for level of significance α = 0.05) the distribution of the all three groups did not have a normal distribution which are shown in Table There are three groups of “Deed Area” variables to compare. The tests that compare the three or more data sets were conducted since more than two sets were involved. The variables of the data sets are independent and include continuous numerical data. As a result of normality test, the non-parametric Kruskal–Wallis tests for several independent samples were performed.A significant difference between the pipelines in terms of the size of parcels for level of significance α = 0.05 according to the test results which are shown in Table In this study, it was mainly examined whether a significant difference between the total affected area and the permanent easement area. Our case is about the comparison of these two data sets, therefore the appropriate statistical tests that compare the two groups were carried out. The variables of the data sets are dependent on each other and include continuous numerical data. Therefore, this study was conducted with the Wilcoxon two related samples test (non parametric test) instead of paired samples t test (parametric test) since the assumptions of the latter test were not met  < α” is for level of significance α = 0.05 the distribution of the difference did not have a normal distribution  affected by the Adıyaman line now have fragments with an area less than 5000 m2, while the same figures are 36 out of the 96 parcels (38 %) for the Iğdır line, and 937 of the 1331 parcels (70 %) for the Sinop line.First of all, the descriptive statistics of the data sets have been obtained . These cases constitute more than 25 % of the cases against The State of Turkey (Yomralıoğlu et al. In studies done on this subject it seems that the size of the parcel is not taken into account. It is significant to be that parcel size remaining out of use is one of the factors weighted with its importance in the planning of pipeline routes.2 due to the drawbacks in term of zoning and agriculture. In this study this was taken as a base and irrespective of the easement width and of the parcel size, the fragments of land with an area less than 5000 m2 did come into being in all the pipelines as a consequence of these construction projects.This study investigated, whether the division into plots of different sizes of parcels through easement rights as a result of the construction of pipelines in rural areas in Turkey has any negative effects on the productive land usage. The current legislation in Turkey regulates the division of land in most rural areas into parcels at least until 5000 mIt was determined that it is necessary to plan the construction of pipelines with due consideration of the possible impact on land use too. Thus, it is needed to include the variable of land use related to the parcel size to the list of the weighted factors in the planning of pipeline routes whether a traditional model or GIS-based technology be employed.The method performed in this study can be used in studies on this subject according to the different parcel sizes that were created by allotment of the parcels due to easement of the construction of pipelines.


The data presented here is related to the research article “An open source cryostage and software analysis method for detection of antifreeze activity”  [1]. The design of the Open Source Cryostage (OSC) is tested in terms of thermal limits, thermal efficiency and electrical efficiency. This article furthermore includes an overview of the electrical circuitry and a flowchart of the software program controlling the temperature of the OSC. The thermal efficiency data is presented here as degrees per volt and maximum cooling capacity. Specifications TableValue of the data•The data may serve as a benchmark for further development of the design, or derivatives hereof.•The data can easily be compared to competing designs, commercial or not.•The information in this article may inspire others to develop their own designs, something the author highly recommends.12T of 60 °C. The power supply was capable of delivering 5 A at varying voltages, all of which were tested. The Peltier module was controlled through PWM, so the duty cycles refer to power draw, relative to maximum.The OSC׳s cooling capabilities were tested under room temperature conditions, with active air-cooling and a large heatsink. The Peltier unit used in the setup was rated for a max ΔSeveral iterations of the OSC were tested before arriving at the design used in this article and the main research article A custom PCB with the form factor of an Arduino shield was produced from the design seen in The OSC has three main settings: LOAD, PID and FREEZE. LOAD will set the temperature of the stage to just below ambient, allowing loading without excessive condensation. FREEZE puts the Peltier unit at maximum power, which will freeze the sample within seconds. PID is the setting which is used during experimentation. A small thermistor provides the Arduino with constant temperature readings, and the Arduino in turn calculates Peltier power level from the temperature deviation from a given setpoint temperature. The setpoint temperature is related to the osmolality of the sample, as described in main article


Epidemiologists have debated the appropriate time-scale for cohort survival studies; chronological age or time-on-study being two such time-scales. Importantly, assessment of risk factors may depend on the choice of time-scale. Recently, chronological or attained age has gained support but a case can be made for a ‘reference relative time-scale’ as an alternative which circumvents difficulties that arise with this and other scales. The reference relative time of an individual participant is the integral of a reference population hazard function between time of entry and time of exit of the individual. The objective here is to describe the reference relative time-scale, illustrate its use, make comparison with attained age by simulation and explain its relationship to modern and traditional epidemiologic methods.A comparison was made between two models; a stratified Cox model with age as the time-scale versus an un-stratified Cox model using the reference relative time-scale. The illustrative comparison used a UK cohort of cotton workers, with differing ages at entry to the study, with accrual over a time period and with long follow-up. Additionally, exponential and Weibull models were fitted since the reference relative time-scale analysis need not be restricted to the Cox model. A simulation study showed that analysis using the reference relative time-scale and analysis using chronological age had very similar power to detect a significant risk factor and both were equally unbiased. Further, the analysis using the reference relative time-scale supported fully-parametric survival modelling and allowed percentile predictions and mortality curves to be constructed.The reference relative time-scale was a viable alternative to chronological age, led to simplification of the modelling process and possessed the defined features of a good time-scale as defined in reliability theory. The reference relative time-scale has several interpretations and provides a unifying concept that links contemporary approaches in survival and reliability analysis to the traditional epidemiologic methods of Poisson regression and standardised mortality ratios. The community of practitioners has not previously made this connection. In recent years, epidemiologists have debated which of the several possible time-scales to use for survival analysis for longitudinal studies and it has been argued that chronological age as the time-scale is preferable to the traditional time-on-study , 2. The Although there is still no general consensus, chronological age as time-scale has gained moderate acceptance for the analysis of survival data from cohort studies. With chronological age as the time-scale, age is usually deemed to be truncated on the left at age of entry to the study. Cox regression is the modelling framework of choice to assess risk factors and the baseline hazard is a nonparametric function of age. This assumption is problematic for long running studies which accrue participants over a period of time since the hazard cannot be a function of age alone but must also depend on calendar time. For example, the mortality rate of a white male of 60 years in California in 1984 would not be the same as that of a white male of 60 years in California in 2004 since longevity would have improved. Using chronological age leaves unresolved the issue of calendar time when participants enter the cohort at different calendar times and this issue is not trivial for studies which span several decades. Cohorts and particularly occupational cohorts, often have these features, that participants join the cohort at different ages and at different calendar times and are followed-up for long periods of time thereafter. One recommendation is to stratify on birth cohort in the Cox regression model using 5 or 10 yearly intervals but, for long running cohorts, this can result in very many strata , althougRelative survival has a long history in epidemiology –13. RelaThe objective of this communication is to compare, as an illustration, a standard analysis using chronological age as the time-scale, left-truncated at age of entry to the study, and with stratification for birth cohort in the Cox model with the analysis of individual survival times on a reference relative time-scale. The intention is to demonstrate that this approach provides a viable alternative to the current standard analysis and is an approach which circumvents much of the controversy surrounding the choice of time-scale. Also, it has appealing interpretations and is connected to the traditional methods of Poisson regression and SMR.This section described more fully the two time scales being compared; the new reference relative time-scale and the chronological age time-scale. Following this the illustrative cohort data is introduced and the statistical analyses of the data are described. The section finishes with a methodological description of the simulation study which was used to establish existence of any bias and the relative power of the two time-scales to detect a differential mortality risk between men and women of light smoking compared to non-smoking.An individual measure of relative survival has been described previously in which, each participant’s actual survival time is transformed to a new scale which is the expected residual cumulative distribution function from a reference population , 20. Thi0 at calendar time s0 and exits at age a1 at calendar time s1 then λ is the hazard in the reference population for a person of gender g, at age a at calendar time s. The reference population may be defined by further demographics such as race and location, but the pertinent point is that the integral is taken over the hazard function for the individual participant’s peer group in the reference population. Thus the individual’s relative time is the cumulative hazard of the peer group in the reference population over the calendar time on study of the individual participant. The survival censoring indicator is the same as that for chronological age, which is whether the individual participant had an event at time s1 or was censored.More specifically, if an individual of gender g enters the study at age aThe reference relative time-scale is the expected number of events for the individual participant during their time-on-study. A reference relative survival time of 1.0 implies that the individual reached their residual life expectancy from entry based on the reference population. A reference relative survival greater than 1.0 implies that the individual had exceeded their residual life expectancy and a value less than 1.0 that they had died or embarked before reaching residual life expectancy.The reference relative time-scale is a weighted version of the real time-on-study. Real time is ‘stretched’ when the hazard  in the reference population is high but time is ‘shrunk’ when the hazard is low. So a calendar time period such as 5 years lived by an older individual participant between 1990 and 1995, has a longer reference relative time value than 5 years between 1990 and 1995 lived through by a younger individual. Shrinking time is a form of accelerating time whereas stretching time, decelerates time.The reference relative time-scale is the reciprocal of an individual participant’s own SMR (divided by 100 if the latter is expressed as a percentage). If the SMR is calculated for a study group of size one then the reference relative time would be the reciprocal of this value. Thus, an individual participant with an SMR of 50 % would have a reference relative survival time of 2.0. For this individual, the reference relative time on study was so long that the individual would have been ‘expected’ to have died twice, with an explanation in the following sense. On calendar time of entry the individual has an expected residual lifetime. If the individual achieves the end of this expected residual lifetime, they would then have a further (but much shorter) expected residual lifetime. If they achieve the end of this second residual lifetime then the reference relative survival time becomes 2.0. A log-linear model for the hazard on the reference relative time scale is therefore also a log-linear model for the individual participants’ SMRs.The reference relative time-scale has a simple game-theoretic interpretation as the final score in a game. In each time period, the individual player joins battle against opponents that are intent on eliminating the individual. The number of opponents is proportional to the hazard in the reference population . If the individual eliminates all the opponents then the player banks points proportional to the number of opponents overcome. The cumulative number of banked points on exit from the game measures the individual’s total success during time-on-play in the game. Censoring applies to the banked points if on exit from the game the individual participant has not been eliminated. So, the reference relative time-scale is the cumulative amount of hazard that the individual has confronted before experiencing an event and is a measure of game success.The transformation, Z, transforms both censored and uncensored survival times to a new relative time-scale, called the reference relative time-scale. Figure Modelling on the reference relative time-scale obtained from the transformation Z has two significant benefits. Firstly, as well as using the Cox regression, relative time can be modelled using the full range of parametric survivals models, such as exponential and Weibull models. Secondly, if risk factors and other variables are all categorical, then modelling reference relative time using an exponential distribution is equivalent to Poisson regression using observed and expected counts. If risk factors and other variables contain quantitative covariates then modelling reference relative times is an extension of Poisson regression to IPD. Thus modelling on the reference relative time-scale can be understood as a generalisation of the traditional Poisson regression method to IPD and to more complex survival distributions. Reference relative survival, therefore, provides a unifying conceptual framework which encompasses both traditional and contemporary methods of analysis.The reference relative time-scale is an example of an alternative time-scale or ‘operational failure time-scale’ which has been discussed in the literature on reliability and performance of systems . It meetCurrently, the conventional approach for survival analysis for cohort data with long follow-up, in which participants enter at different calendar times and where ages at entry are variable is to use the time-scale of chronological age with left truncation for age at entry. With this approach adjustment for birth cohort is made by using a stratified Cox model with 5 or 10 year intervals , 5 or inAnalyses of a long running cohort of British cotton mill workers (1966–2007) have been previously described. The cohort was founded with the aim of understanding the long-term effects of exposure to environmental particulates on respiratory mortality and morbidity. The cohort has provided evidence that working with cotton reduced the risk of lung cancer death and that light smoking at baseline predicted higher mortality for women compared to men –23. Thes1% predicted) and the ratio of FEV1% predicted to forced vital capacity (FVC). Participants alive at age 90 were censored. Table Ages at entry to the cohort were in the range 15–81 years  over the period 1966–1974 and participants’ year of birth was in the range 1885–1954. Smoking consumption was categorised at baseline as non-smoker, light (1–14), medium (15–24), heavy (25+ cigarettes per day) smoker and former smoker. The cohort contained both men and women mostly working full-time in all of the mill environments. Other variables measured at baseline included; the presence of the lung disease of cotton mill workers known as Byssinosis, the presence of cough and phlegm for at least 3 days per week for at least 3 months of the year, how long the worker had worked in the cotton industry and lung function expressed as forced expiratory volume in one second adjusted for age, gender and height  for light, medium, heavy and former smoker relative to non-smoker together with HRs for other risk factors measured at baseline. The analyses also estimated the women to men relative risk ratios (RRR) for the four baseline categories of cigarette consumption; light, medium, heavy and former smoking. The relative risk ratio was defined by RRR = HR of female smokers to female non-smokers/HR of male smokers to male non-smokers where HR was the hazard ratio. The RRRs were the single degree of freedom components of the interaction between gender and consumption category and were estimated using indicator variables. Both analyses fitted the Cox model, but the Weibull and the exponential models were also fitted for the survival times on the reference relative time-scale. The analyses were performed in the R programming language and environment .In order to compare the bias and power of the reference relative time-scale to that of chronological age at risk time-scale a simulation study was carried out. Each simulation included all the participants from the illustrative cohort together with the participant’s age at entry, gender and date of entry to the study being kept fixed at their observed values. All the participant’s covariate and factor values were also kept fixed at their observed values. Each participant’s lifetime from date and age of entry was then simulated according to a model which calculated the participant’s hazard of dying in each calendar month following date of entry. For each month, in turn moving forward in time, a uniform random variable was generated. The first month, in the sequence, for which the random variable was less than the monthly hazard was selected as the simulated time of death. Once simulation of time of death was completed for all participants, a model was fitted by Cox regression using the reference relative time-scale and by a stratified Cox regression using the age at risk time-scale.0, α1, α2, α3, α4 respectively and where α0 = 1. These parameters applied to both males and females except in the case of light smoking females for whom the relative parameter was βα1. In the simulation α0, α1, α2, α3, α4 were kept fixed at the values of 1.00, 1.24, 1.83, 2.08 and 0.93. Each simulation was for a fixed value of β in the range 1.0–1.4. The actual hazard used in each month was obtained from these model parameters and the numbers of participants in each gender and smoking category in the illustrative cohort. For males, if there were n0, n1, n2, n3, n4 in the categories; non-smoker, light smoker, medium smoker, heavy smoker and former smoker and the monthly hazard in the reference population was hm then the hazard for non-smokers, h0 was computed by.In the simulation, the monthly hazard for each participant was calculated from a combination of the model parameters and the England and Wales reference population monthly hazards. The model assumed that the hazard of dying was proportional to smoking status; non-smoker, light smoker, medium smoker, heavy smoker or former smoker with relative parameters α1h0, α2h0, α3h0 and α4h0 respectively. For females the calculation of the hazard was analogous except that α1 was replaced by βα1. This method of calculating the relative hazards had the effect that the average over a cohort with the observed mix of smoking grade would equal the reference population monthly hazard. This method generated realistic lifetimes with the appropriate relative hazards given by the model parameters. This allowed the two methods to be fairly compared in terms of their power to detect a value of β greater than 1.0 which would indicate a gender difference in the relative risk of light smoking and any bias in the estimation of β. It also allowed a check on the power of the null value of β = 1. For each value of β, 200 simulations were carried out and testing to estimate power used a 5 % significance level for the test.The hazards for light smokers, medium smokers, heavy smokers and former smokers were given by αThe simulation also provided an opportunity to compare the methods when the reference population used to obtain the reference relative times was not an appropriate population for the cohort under study. This was achieved by increasing the monthly hazard of dying in the simulation by an additional multiplying factor which was an exponential function of age; exp (0.002 × age). This increased the hazard by about 4 % at age 20 and 13 % by age 60. This produced disproportionately shorter simulated lifetimes than in the reference population used to obtain the reference relative time-scale.A comparison of the fitted Cox model using the reference relative time-scale with the stratified Cox model using chronological age as the time-scale is presented in Table The fitted model coefficients for two alternative fully parametric survival models, the Weibull and the exponential, when fitted to the reference relative times, are shown in Table The fully-parametric models included a constant term and so the predicted percentiles of the survival distribution were computed. The percentiles were back transformed using the reference population hazards in order to build mortality curves as a function of age. This was especially easy to execute since a parametric survival model had been fitted and demonstrated the advantage of the reference relative survival time followed by parametric survival modelling. Figure The exponential model shown in Table For the values of the parameter β = 1.20 and β = 1.40, the estimated power was very similar when the simulated lifetimes were analysed using chronological age at risk as time-scale or the reference relative time-scale  models, which index an event count by age, calendar period and birth cohort, have an extensive literature  and haveThe use of a reference population to gain insight into the risk factors affecting a study cohort begs the question of whether results from the study group can be generalised to the reference population. This would seem likely if it could be assumed that the study group is, in some sense, a sample from the reference population, but might the generalizability be conditional upon certain other assumptions? It would be reasonable to use a reference population to create a relative time-scale so long as there was a sound belief that the hazards in the study group were proportional to those in the reference population. If this was the case, would generalisation to the reference population be valid also?It may be worthwhile considering whether the definition of the reference relative time-scale as the integral over a reference population hazard could be extended to include an additional term under the integral for the quality of life of the individual as a function of age. The transformation to the reference relative time-scale stretches time when the population hazard is high and this effect is greater for older compared to younger individuals. A quality of life function could act as a penalty to reduce some of the stretching and would change conclusions regarding risk factors of interest when regression models are fitted on the reference relative time-scale. It is clear, therefore, from these discussions that the reference relative time-scale not only provides a viable alternative to modelling chronological age or real time-on-study but is an interesting concept in its own right that points the way to several avenues of future research which others may wish to explore.The reference relative time-scale was shown to provide a viable alternative to the current standard method which uses chronological age as the time scale with left truncation for age at entry and a Cox model stratified on birth cohort. Its use led to a simplification of the modelling process and the scale possessed the defined features of a good time-scale as defined in reliability theory. Simulation suggested that the two methods have similar power and are equally unbiased. The reference relative time-scale has several interpretations and provides a unifying concept that links contemporary approaches in survival and reliability analysis to the traditional epidemiologic methods of Poisson regression and SMRs and can be understood as an extension of these traditional methods. The community of practitioners has previously failed to make this connection.


This study examined the usefulness of the fibula positioning guide for boosting the accuracy of mandible reconstructions.N = 15) and control (N = 15) groups. For reference, we prepared a reconstructed mandibular RP model with a three-dimensional printer, based on surgical simulation. In the experimental group, a fibula positioning guide template and fibula cutting guide, based on simulation, were used to reconstruct the mandible with a fibula graft. In the control group, only the fibula cutting guide, with reference to the reconstructed RP mandible model, was used to reconstruct the mandible with a fibula graft. The two mandibular reconstructions were compared to the surgical simulation by registering images with the non-surgical right side of the mandible. On the reconstructed side, 3D measurements were compared between the surgical simulation and actual surgery, and the sum of differences was taken as the total error.Thirty mandibular rapid prototype (RP) models were allocated to experimental (p = 0.015). The greatest point error was the vertical error at the mesial point of the anterior fibula segment. The anteroposterior and lateral errors were not significantly different between groups. These results showed that these two methods were not significantly different, except in the total and vertical errors.The combined use of the fibula cutting and positioning guides produced a smaller total error (mean ± SD: 10.0 ± 7.9 mm) than the fibula cutting guide alone (12.8 ± 8.8 mm; Considering the CAD/CAM processes required for creating positioning devices, the benefit provided with a positioning guide justified its use over the fibula cutting guide alone. The wide distribution of computed tomography (CT) imaging services and advancements in computer technology in recent years have offered surgeons the ability to conduct preoperative surgical simulations. Surgical guides can be manufactured with the use of computer-aided design (CAD) and computer-aided manufacturing (CAM) technologies. These guides help surgeons adhere to surgical simulation plans in actual surgeries for craniofacial reconstructions , 2.The free fibula flap is one of the most commonly-used grafts in mandibular reconstruction. It offers several advantages over other flaps, including a bone length sufficient for mandible reconstruction, a high survival rate, and attached skin for concurrent skin grafting . MandiblIn the present study, based on CT data, we conducted a surgical simulation of a mandibular reconstruction with a fibula graft. In addition, we used CAD/CAM techniques to manufacture a fibula cutting guide and a fibula positioning guide to facilitate cutting and placing the fibula segments into the correct location during mandible reconstruction, according to the surgical simulation. The results elucidated the usefulness of a fibula positioning guide in boosting the accuracy of mandible reconstructions.N = 30) of rapid prototype (RP) models of mandibles with partial defects on the left side  and the other to the experimental group (N = 15).Based on CT data of 15 mandibles, we prepared computer-assisted 3D-image reconstructions of mandibles with a defect on the left side Fig. . We thenide Fig. . Each paN = 15 models each).The CT data for one left fibula were used to prepare a computer-assisted 3D reconstructed image the fibula. Again, the STL data and the same 3D-printer (ProJet 360) were used to manufacture 30 RP models of the fibula. These were assigned to control and experimental groups  We acquired CT DICOM data by scanning the mandible and fibula models . (2) We opened the mandible and fibula DICOM files with Mimics version 14.0 software  to convert them into 3D images. (3) To reconstruct the left mandible (defective area) in the simulation surgery, first we cut the mandible image from the right 1st premolar to the left inferior condylar neck area Fig. . (4) We We manufactured a fibula cutting guide to facilitate cutting the fibula according to the surgical simulation. First, we designed the fibula cutting guide in the Mimics software. We moved the fibula bone fragments that were used to reconstruct the left mandible to their original positions in the intact fibula bone. We rendered planes that would guide cutting, based on the cross sections of the fibula fragments Fig. . We usedFor the surgery, we cut the fibula RP model according to the manufactured fibula cutting guide with a fissure bur, an industrial compass saw, and a surgical osteotome. We performed the osteotomy on the RP mandible according to the mandibular surgical simulation, by visually referring to the reconstructed RP model. We used an industrial-grade compass saw to remove the defective left mandibular area, as per the manual. The mandible was cut from the right anterior 1st premolar to the left condylar neck. The cut fibula bony segments were placed with reference to the reconstructed RP model. Then, titanium mini plates  were bent to fix the fibula bony segments Fig. , with twTo facilitate placing the fibula segments into the mandible, we designed a fibula positioning guide for each mandible in a reconstruction simulation. The positioning guide comprised five supports that fit onto the remaining right inferior border of the mandible, the three fibula segments, and the left condylar region. These components were stabilized into the correct positions by connecting them to supporting poles Fig. . Based oFor the surgery, in the same manner as in the control group, we first cut the RP mandible, and then we cut the RP fibula model with the fibula cutting guide. Next, we placed the remaining regions of the mandible RP model and the cut RP fibula segments in the positioning guide. Finally, we fixed all the components in the same manner as described above for the control group Fig. .Fig. 7ExWe acquired CT images of the RP mandible models after reconstruction surgery. The images were acquired under the same conditions as those used before the experiment. We imported the DICOM file of reconstructed mandible model into the Mimics software to convert it to 3D images, and we exported it in the STL file format. We also exported the surgical simulation data to an STL file. With XOV2 software , we superimposed the actual surgical data onto the surgical simulation data and registered them based on the non-operated right mandibular region Fig. .Fig. 8SuWe opened the superimposed mandible data  in the Mimics software. We compared the surgical result to the simulation by setting a reference plane in the cranial area and calculating the distances between the plane and several measurement points on the reconstructed mandibles. The error was taken as the difference between the measurements taken at corresponding points on the postoperative model and the surgical simulation. Three reference planes were established Fig. : the horMandibles were measured at the lateral points of each fibula segment and the lateral pole of the left condyle Fig. . One indt-test to compare the measurements obtained with the two methods. The significance level was set to 0.05.We evaluated the errors in control and experimental groups to determine whether the fibula positioning guide offered any benefit in the mandibular reconstruction. We used a To measure the error in placing the measurement points by the surgeon, the surgeon repeatedly (10 times) set a reference point on the left condylar head area; the error was measured by calculating the differences in the reference points.The error arising from performing the osteotomy without the use of a mandible cutting guide was computed by measuring the distances between the cut right mandibles in the surgery simulation and the postoperative model. The error in superimposing the mandibular images was analyzed by examining the total 3D error in the right mandible reference area.p = 0.015; Table First, we compared the 3D distance errors  between the control and experimental groups Table . When bop = 0.002). There were no significant differences between the groups at any other measurement point, except at the mesial point of the anterior fibula segment. The errors for segments posterior to the distal point on the middle fibula segment ranged from 2 to 5 mm in the experimental group and from 6 to 8 mm in the control group.We examined the vertical distances from the previously-established horizontal plane, and calculated the error differences between the surgical simulation and the postoperative data Table . The meaThe overall mean anteroposterior errors  were not significantly different between the two groups at each measurement point Table . The errThere were no significant differences between groups in the lateral errors  at each measurement point Table . The groWe measured the linear angle of each segment axis compared to the corresponding axis in the simulation, and found no significant angular errors with either method Table . There wp = 0.138).We also calculated the error in cutting the mandible by examining the differences between the surgical simulation and postoperative data. The mean (±SD) total 3D error in the right mandible cut was 1.1 ± 0.6 mm in the experimental group and 0.8 ± 0.5 mm in the control group; thus, the errors were not significantly different between the two groups (The mean (±SD) error arising from setting the measurement points by the surgeon was found to be 0.2 ± 0.1 mm.The mean (±SD) total error in the superimposition of the reference areas  of the model and simulation images was 0.009 ± 0.601 mm.This study examined the precision of a fibula positioning guide in mandibular reconstruction with the fibula graft. We found significant errors between reconstructions performed with or without the positioning guide, in the mean total 3D distance and the vertical error at the mesial point in the anterior fibula segment.In both groups, the 3D distance errors increased from the anterior to the posterior segments. At the points posterior to the middle fibula segment, which are considered the posterior mandible area, both groups showed a mean error greater than 12 mm. When only a fibula cutting guide was used, the error in the condylar head area was about 19 mm. In the present study, the position of the condyle was not fixed; instead, it was held by hand in position within the glenoid fossa to form the temporomandibular joint. Thus, the largest error was observed in the condylar area. This error was believed to be similar to the error associated with movement of the condylar head in the temporomandibular joint. This observation indicated that the condylar head is prone to displaying the greatest error in actual clinical cases.When only the cutting guide was used, the mean vertical errors in the posterior mandible area were greater than 6 mm. When both the fibula cutting guide and the positioning guide were used, the mean vertical errors for the same region ranged from 2 to 5 mm. This pattern was similar to that observed in the 3D distance errors, and it indicates that the potential for error increased in the posterior direction. Consequently, in actual clinical cases, we can expect a greater potential for error in positioning segments in the posterior mandible.There were no significant intergroup differences in the anteroposterior error at each measurement point. When a fibula positioning guide was used in the experimental group, the errors were somewhat higher than control group errors at points between the middle fibula and the condylar head areas (range 3 to 4 mm). On the other hand, when only the fibula cutting guide was used (control group), the errors in all measurement areas were ≤3 mm. This suggested that, in real clinical cases, it might be more beneficial to adjust the anteroposterior position of the fibula fragments by referring to the 3D-printed reconstructed model, rather than using a positioning guide.There were no significant differences in lateral errors between groups at each of the measurement points. In both groups, the errors for the distal point of the anterior fibula segment (−1.7 mm) and the mesial point of the middle fibula segment (−2 mm) were similar in magnitude. The negative values indicated a medial displacement after surgery. Moreover, in both groups, the errors for the segments between the mid fibula segment and the condylar head were positive, indicating a lateral displacement after surgery. Therefore, in real clinical cases, the segments may change from a medial displacement in the anterior mandible to a lateral displacement in the posterior mandible, indicating an increasing lateral displacement.There were no significant angular errors in any segments with either method. When only the fibula cutting guide was used, the error was approximately 9° for the anterior and mid fibula segments, and approximate 12° for the posterior segment. When the positioning guide was used, the error ranged from around 7 to 9°. The results of this experiment implied that, in real clinical cases, there may be an axis error of about 10° in each fibula segment.A mandibular cutting guide may be required for mandibular osteotomy. In the present study, the average error in the right mandible area was about 1.1 mm; the same error was 0.8 mm in the control group. This result may imply that a fibula cutting guide is not required to enhance the precision of the mandibular osteotomy in an actual surgery.Severe soft tissue damage may accompany mandibular reconstruction. In such cases, the surgeon must consider facial soft tissue in addition to reconstructing the mandible using a fibula. However, the present study only examined whether the fibula bone segment can be placed in the appropriate position, in accordance with the simulation surgery, in mandibular reconstruction. In other words, this study is limited to the reconstruction of hard tissue. Studies with actual clinical cases using fibula positioning devices are needed to examine facial reconstruction involving the fibula and soft tissues.In this study, the three-dimensional distance error was significantly small when the positioning device was used. There was no statistically significant difference in the anteroposterior error, lateral error, and vertical error from each plane. However, the errors were smaller in general when the positioning device was used. This may be a statistically significant outcome, depending on the numbers included in the experimental and control groups. This study had 15 models for each group, and in such cases, the effect size is 0.94 when α (significance level) is 0.05 and β (test power) is 0.2 according to the statistical power analysis. If the value of n is increased, the effect size will be reduced, which can lead to statistically significant errors in each plane. Therefore, it may be difficult to challenge the usefulness of a positioning device based on this study’s results.This study used a rapid prototyping model. In actual clinical cases, it may be difficult to use a positioning device when a fibula flap with soft tissue is used. However, we believe that if the design is changed to address the positional relationship between the device and the flap, a better surgical device can be manufactured. Depending on its position, the surgical device may interfere when a reconstruction plate is used; although, there should be no problems with the current design if a miniplate is used. Furthermore, the device design can be adjusted if a reconstruction plate is necessary.Recently, the use of preoperative 3D surgical simulations for the manufacture of surgical guides has been on the rise , 10. TheEssentially no clinical studies have described the use of the fibula positioning guide designed in the current study. However, Zheng et al.  reportedThe present study used two mini plates for each connection between fibula segments and between end segments and the mandible. This method for fixing the fibula segments could be modified as reconstruction plate for a better clinical result . RecentlIn the present study, all surgeries were conducted by a single surgeon. Some error may have been introduced, due to the surgeon’s level of proficiency. For instance, small inconsistencies in the contact angles or protrusions in the plating may have altered the abutment between the mandible and anterior fibula segment or between fibula segments. Also, the type of plate and the design of the surgical guides may have introduced errors.If a reconstruction plate is used, the plate itself can act as a positioning guide for the fibula bone segment through pre-bending. In the present study, the positioning guide was used to secure the bone segment using a miniplate. The miniplate is fixed on the fibular lateral surface, so the positioning guide is presumed to be helpful. If a reconstruction plate is used, the design of the positioning guide can be adjusted to suit the position of the plate. Furthermore, for CAD/CAM reconstruction plates, which are manufactured to guide the position angle of the fibula bone segment according to the simulation outcome, a separate positioning guide may not be necessary.The present study only sought to determine whether the fibula bone segment can be accurately positioned, according to the surgical simulation results, in cases of mandibular reconstruction using a fibula. The scope of the study is limited to the reconstruction of this hard tissue and the findings are not supported by actual clinical outcomes. If soft tissue is included with the fibula for the mandibular and facial reconstructions, there may be interference when positioning the cutting guide and positioning device on the fibula. Moreover, there may be difficulties in positioning the surgical device on the flap when thick muscle fibers are attached to the lateral surface of the fibula. A cutting guide can assist with accurate angles and positions, even with a small gap in between. However, a positioning device may incur greater error if soft tissues or thick muscles are attached to the fibula because the device is designed based the position of each fibula bone segment. Fixation plates, such as the miniplate or reconstruction plate, and screws limit the region of its placement. The usefulness of a positioning device may be different for each patient, as the fibula flap varies. Thus, CAD/CAM reconstruction plates may be a great alternative because they also guide the fibula bone segment to the accurate position and angle determined by surgical simulation.Results of actual clinical cases are needed to evaluate the use of fibula positioning devices for facial reconstructions when soft tissues are included in the flap. In an actual surgery, the soft tissues may cause interference, so the positioning device must be designed in consideration of this. The positioning device was manufactured based on the simulation results using the patient’s actual CT data, so it is presumed there will be similar clinical outcomes as shown in the present study when only the bone segments are reconstructed using the fibula or when a fibula with little muscle fibers is used. In addition, future designs of the positioning device should be adjusted based on the soft tissue data.In the present study, the condyle head was not fixed. Therefore, its position and movements may be different in an actual surgery, which is a limitation of this study. This study examined mandible reconstruction with subcondylar osteotomy, not a condylectomy, because mandible reconstruction accompanied by a condylectomy requires the fibula bone segment to be positioned on the glenoid fossa, but this distance and the three-dimensional position was not clearly identified. It is predicted that the error will be different in an actual surgery with condylectomy. Moreover, there may be a long-term error depending on the bone absorption in the distal end of the fibula bone segment, movement at the inner glenoid fossa, and changes in the glenoid fossa. These problems could be examined in an additional study on surgical planning with reference to the long-term prognosis. Although this study could not verify the stability of occlusion, we believe there will be stable occlusion if there is intermaxillary fixation with the side of the mandible that was not osteotomized, there is constant assessment, and implants and prosthetics are used when needed.In the present study, only one surgeon manually fixed each bone segment, drilled, and inserted the screws simultaneously; therefore, there could have been error during the process of drilling and fixing each segment on the miniplate or in the manual holding of segments. However, this should not have induced a large experimental error because such errors can also be induced in the actual surgery. The outcomes of an actual surgery are presumed to be similar to that of this study if the condyle head is well fixed on the fossa and is not displaced significantly.This study aimed to examine the value of using a fibula segment positioning guide in mandibular reconstructions with fibula grafts. We found significant difference in the errors between reconstructions performed with or without the positioning guide, in the mean total 3D distance and the vertical error at the mesial point of the anterior fibula segment. Considering the CAD/CAM processes required for creating positioning devices, the positioning guide provided significant benefit over the use of a fibula cutting guide alone.