The detection precision of the tracking error when using the BEV images was <0.2 mm. These two detection precisions were derived from our measurement system and were not obtained from the SRTS. The median of Ep95 was found to be 1.5  mm. The difference between the minimum and maximum Ep95 was 2.5 mm, indicating that this provides a better means of evaluating patient‐specific SRTS accuracy. A suitable margin, based on the predicted patient‐specific SRTS accuracy, can be added to the clinical target volume.The accuracy of the CyberKnife Synchrony Respiratory Tracking System (SRTS) is considered to be patient‐dependent because the SRTS relies on an individual correlation between the internal tumor position (ITP) and the external marker position (EMP), as well as a prediction method to compensate for the delay incurred to adjust the position of the linear accelerator (linac). We aimed to develop a system for obtaining pretreatment statistical measurements of the SRTS tracking error by using beam's eye view (BEV) images, to enable the prediction of the patient‐specific accuracy. The respiratory motion data for the ITP and the EMP were derived from cine MR images obtained from 23 patients. The dynamic motion phantom was used to reproduce both the ITP and EMP motions. The CyberKnife was subsequently operated with the SRTS, with a CCD camera mounted on the head of the linac. BEV images from the CCD camera were recorded during the tracking of a ball target by the linac. The tracking error was measured at 15 Hz using in‐house software. To assess the precision of the position detection using an MR image, the positions of test tubes (determined from MR images) were compared with their actual positions. To assess the precision of the position detection of the ball, ball positions measured from BEV images were compared with values measured using a Vernier caliper. The SRTS accuracy was evaluated by determining the tracking error that could be identified with a probability of more than 95% (Ep95). The detection precision of the tumor position (determined from cine MR images) was PACS number: 87.53.Ly The CyberKnife Robotic Radiosurgery System  is a frameless image‐guided stereotactic radiotherapy system. A 6 MV linac is mounted on a high‐precision, six‐axis robotic manipulator arm. Beams are accurately delivered to the target through the collimator. Originally, the CyberKnife was used to treat brain and head/neck tumors.The SRTS is a CyberKnife subsystem, developed to irradiate extracranial tumors that move as a result of respiration. It continuously synchronizes the beam delivery with the moving tumors. With the SRTS, patients can breathe normally during treatment, and the treatment margins are reduced through precise tracking.The SRTS relies on the correlation between the ITP and the EMP. Before the start of each treatment fraction, the ITP is measured by using orthogonal X‐ray images at no fewer than eight data points. The external chest/abdominal marker is continuously monitored by using optical LEDs. The correlation model is a linear or polynomial fit between the 3D ITP and the simultaneous EMP, and is automatically established by the system. It is updated by acquiring additional X‐ray images during treatment. At our institution, this is typically done every 45 to 60 sec. The SRTS estimates the ITP from the EMP by applying a correlation model, and then delivers the beams to the moving tumor. However, the necessary data processing, communication with the robotic controller, and the inertia of the robotic manipulator and linear accelerator all contribute to the delay that is incurred when determining the position for the beam. Therefore, a prediction method is employed to compensate for this delay.The accuracy of the CyberKnife was first evaluated in 1996,Any poor correlation between the ITP and EMP and/or an irregular breathing pattern could have an adverse effect on the precision of the dose delivery because the SRTS utilizes both a correlation model and the prediction method. Therefore, it is possible that the SRTS accuracy is patient‐dependent, meaning that the treatment margin should be changed for each individual. Most previous reports evaluated the SRTS accuracy retrospectively and no studies attempted to estimate the pretreatment SRTS accuracy.The purpose of this study was to develop a system for performing pretreatment statistical measurement of the SRTS's tracking error and so enable the patient‐specific prediction of the SRTS accuracy.We analyzed 23 lung treatment patients for whom it was possible to obtain respiratory motion data from cine magnetic resonance (MR) images and who had been treated with the current version (3.1.1) of the SRTS between September 2013 and July 2014. The median age of the 23 patients was 74 yrs . The tumors were located in the right lower lobe of the lung in ten patients, in the left lower lobe in six patients, in the right upper lobe in three patients, in the left upper lobe in three patients, and in the right middle lobe in one patient. All of the study participants provided informed consent, and the design of the study was approved by our institutional review board. We used not only respiratory motion data from the patients receiving treatment, but also sinusoidal wave data as a basic case for this study.We used the CIRS Dynamic Thorax Phantom Model 008A  as a dynamic motion phantom (DMP). This DMP consists of two separate platforms, namely a target motion simulator and an external skin motion simulator; these are independently controlled by CIRS motion‐control software. The DMP generates three‐dimensional target motion and has a manufacturer‐stated absolute position accuracy of 0.1 mm. Motion range was up to 50 mm, 10 mm, and 10 mm in the craniocaudal (C–C), anterior–posterior (A–P), and left–right (L–R) directions, respectively. The DMP applied different waveforms to C–C, A–P, and L–R. In addition, the amplitudes and phase shifts for the C–C, A–P, and L–R directions were adjusted independently.A 20 mm diameter plastic ball, with a gold marker at its center, was used as the target. The ball was set up on a platform to simulate the target motion, and three optical markers were set up on the platform to simulate the external skin motion . The DMPSinusoidal wave data: the range of motion was 20 mm and 10 mm for the superior–inferior (S–I) direction (with the target motion simulator) and A–P direction , respectively; the motion frequency was 16 cycles/min.(228 to 333)×500 mm; flip angle: 20°; bandwidth: 449 Hz; image matrix: (176 to 256)×384; image acquisition time: 0.2 to 0.3 sec; slice thickness: 8 mm. The sagittal plane was set to that plane which passes through the center of the tumor. We acquired 512 continuous images. This scan was repeated three times, and then the three sets of images were merged.Respiratory motion data: an MR scan was performed with a 1.5‐Tesla whole‐body clinical MR scanner  using a CP body array flex coil and a spinal coil for the lung tumor patients. The sagittal plane was obtained by true fast imaging with a steady‐state precession sequence. The sequence parameters were as follows: repetition time/echo time: 4.3 ms/1.73 ms; field of view: A test tube containing a contrast agent was placed on the surface of the patient's abdomen as an external marker. The position was almost the same as that of the external marker for the SRTS. The diameter of the test tube was 14 mm. All of the sagittal plane images included both the tumor and the test tube.Respiratory motion data for the ITP and EMP were collected from the cine MR images using BreathingData (software developed in‐house by author M. I. for this system) that implements template matching based on a zero mean normalized cross‐correlation function. Template matching was implemented by first picking out parts of the tumor and external marker to use as a template. The software then searched for similar regions on the other images, by comparing them with the tumor template and external marker template; this was done for every image. BreathingData determined the tumor and external marker positions by calculating the position of the centroid of some of the pixels constituting the tumor and external marker. The sagittal plane yielded the simultaneous motion of the lung tumor in the C–C and A–P directions and the motion of the surface of the chest/abdomen in the A–P direction.To reduce noise, smoothing was applied to all of the respiratory motion data by using a simple moving average, which was the unweighted mean of the two points. Then, respiratory motion data were calculated for 0.033 sec intervals by using cubic spline interpolation for the dynamic motion phantom. Respiratory motion data were obtained from continuous imaging of three sets for about 330 sec. Treatment plans were created based on static CT scans and standard CyberKnife treatment parameters. Each plan utilized ten beams, with several different source positions. All of the beams in this plan aimed at the center of the ball. All of the beams were set to 200 MU for 15 sec of data acquisition.The DMP motion used sinusoidal wave data for a simple case and the patients’ respiratory motion data for a clinical case. Then, the CyberKnife was moved under the control of Synchrony in demonstration mode, with a CCD camera  mounted on the head of the linac  images from the CCD camera were recorded as the linac tracked the ball. The central axis of the CCD camera (center of BEV image) was matched to the central axis of the linac beam by using a custom‐built jig. The ball was stationary at the center of the BEV image when tracking was complete, but would be shifted from the center of the BEV image when the tracking was not complete. The tracking error was defined as the distance from the center of the BEV image to the center of the ball in the BEV images. The tracking error was measured at 15 Hz using VideoCapture . The software used a A test tube containing a contrast agent and an acrylic cube phantom filled with water were placed on the MR couch. The test tube was too small to produce an MR signal, so we used the acrylic cube phantom filled with water. The test tube was rotated relative to the A–P axis as the test tube position was shifted 0.5 mm in the C–C direction in sagittal plane, which was moved 5 mm in L–R direction. Sagittal images were taken for 13 different planes at 5 mm intervals. The MR sequence was used to obtain respiratory motion data for each patient. The test tube position was determined from MR images using BreathingData and was compared with the nominal test tube position.−7 mm to +7 mm in increments of 0.5 mm. A Vernier caliper was attached to the target simulator to obtain the true value of the movement of the ball. A CCD camera was mounted on the linac head, placed perpendicular to the axis of movement of the ball. The orientation of the CCD camera was adjusted to be parallel and perpendicular to the axis of movement of the ball on the BEV image. The ball positions were determined from the BEV images using VideoCapture and were compared with the values measured by the Vernier caliper.The ball was placed on the target motion simulator of the DMP and was moved within a range of We calculated the tracking error that could be tracked with a probability in excess of 95% (Ep95) for each beam direction. The SRTS accuracy was defined as the median value of Ep95 for ten beams (Ep95med).0.00±0.13 mm. The difference for every position was less than 0.2 mm.0.05±0.07 mm and 0.01±0.12 mm in the horizontal and vertical directions, respectively. The minimum and maximum values of the position differences were −0.05 mm to 0.21 mm and −0.19 mm to 0.21 mm in the horizontal and vertical directions, respectively. The maximum absolute difference for all positions was 0.21 mm. However, the difference was less than 0.2 mm within a range of −5 mm to 5 mm.Representative BEV images from the CCD camera are shown in median=3.9 mm) for the A–P direction, and from 3.0 mm to 29.0 mm (median=9.4 mm) for the C–C direction. The median of the motion frequency was 15 cycles per min (range 7 to 35). Ep95med for the sinusoidal wave data was 1.0 mm. −5 mm to 5 mm. Therefore, the precision of our method was determined as being acceptable for statistical measurement of the SRTS's tracking error.The position difference between the values measured from MR images using BreathingData and the nominal test tube position was less than 0.2 mm in all positions. The difference between the values measured for the ball position with a Vernier caliper and those measured from BEV images using VideoCapture was less than 0.2 mm over a range of >10% even for a displacement of as little as 1 mm. A displacement of 1 mm in the direction of the central beam axis could lead to a difference in the dose of <1%. Therefore, the use of a 2D BEV image is acceptable for clinical use.One of the limitations of this study was that we could not evaluate the tracking error in the direction of the central beam axis because the target motion was captured by a 2D BEV image. The average value of Ep95 for Beam 4 was the smallest; the angle of Beam 4 and the C–C direction of DMP were smaller than those of the other beams. This result indicates that the target motion captured by a 2D BEV image would change depending on the direction of the target motion and/or the irradiation angle. In other words, the dosimetric consequences may be overestimated as a result of a very slight movement of the target when the tracking depends on the irradiation angle but the tracking error is assessed only from the log files. Although a tracking error in the vertical direction could affect the dose delivery, a tracking error in the direction of the central beam axis could have no adverse clinical impact. Because the CyberKnife's beam profile is not flat, a steep falloff of the penumbra could shift the dose by Previous reports suggested that the respiratory external marker motion does not always accurately correspond to the 3D internal target motion and that this may affect the SRTS accuracy.The Ep95med in our study was 1.5 mm, larger than that obtained with a similar phantom in a previous report.Although the respiratory motion data for Patient 18 exhibited an irregular breathing pattern, the value of Ep95med was 1.5 mm. Wong et al.The difference between the minimum and maximum value of the Ep95med was 2.5 mm. This difference indicates that the SRTS accuracy is patient‐dependent. Therefore, we concluded that it was better to measure the SRTS tracking error before any treatment, to enable the prediction of the patient‐specific accuracy. Furthermore, it was better to add a suitable margin for each patient. As such, our institution adds the value of Ep95med to each patient as a margin for the tracking error.The SRTS's tracking error can be statistically measured prior to treatment. A suitable margin can then be added according to the predicted patient‐specific SRTS accuracy. The application of a suitable margin to the clinical target volume will prevent surrounding structures from being affected.Supplementary MaterialClick here for additional data file.


This study aimed to determine whether sex, hand length and the individual training status affect hand strength and whether these measurements differ if they are recorded using the Jamar dynamometer or a new cylindrical measuring system.p ≤ 0.05 was considered statistically significant.For this purpose, 152 healthy adults were examined using a new manugraphy measuring system  comprising two measuring cylinders of different sizes and a Jamar electronic dynamometer with two grip positions corresponding approximately to the sizes of the cylinders. A descriptive analysis was performed as well as a correlation analysis using the Pearson correlation coefficient. To prepare predictive models, multiple linear regression analyses were carried out to determine factors that influence the force and A significant difference in the maximum and mean strength was observed that is dependent on sex, with men stronger than women, in line with expectations, and hand length, with small hands able to exert less force than large hands. No consistent increase in strength could be attributed to repetitive manual loads applied either at work or in leisure activities.Both measurement techniques yielded similar results, suggesting that manugraphy is well suited for clinical research purposes because it not only takes measurements that are just as reproducible and valid as the conventional measurement technique but in doing so measures not just the total strength of a hand but also enables more precise comparisons of isolated hand regions applying dynamic measurements. To be able to estimate changes in hand function after injuries, over the course of healing or as part of an expert examination, objective measurement techniques are required, ones that also allow classification of the results of scientific studies when comparing different treatment options. The loss of strength in the hand with the power grip is an important reduction in the overall functionality of a hand . MeasuriBefore using the device clinically, the physiological parameters that influence grip strength need to be determined. Previous studies using the manugraphy system have confirmed that age does not correlate with hand strength  and thatThe aim of the study was to determine whether sex, hand length and repetitive loading of the hands at work or during leisure activities, that is the training status, affect hand strength and whether these measurements differ if they are recorded using the Jamar dynamometer or the manugraphy system.In this 2-centre study, 152 healthy subjects were recruited in two hospital setting, one localized at the Baltic Sea in north-eastern Germany, the other in a rural district located in central Germany. We studied a population of healthy male and female subjects working as members of the medical and sports science departments of the faculty as well as construction workers, office employees and students who participated voluntarily without payment. Exclusion criteria were a history of injuries or existing diseases of the upper extremities, the presence of myofascial syndromes, rheumatic disease, multiple sclerosis or malignant underlying diseases. The subjects’ handedness and the length of both hands in centimetres (cm) were recorded. The distance between the wrist fold and the tip of the middle finger with the hand held straight and stiff was measured in centimetres (cm). Hands with a length ≤ 17.5 cm were defined as small while hand lengths of 17.5 cm to ≤19 cm were classified as medium and hand lengths > 19 cm were defined as large.activities without special manual loading, no sports at allactivities with changing manual loading, sports without manual loadingactivities with constantly repeated manual loading without greater force expenditure, sports with manual loadingactivities with constantly repeated manual loading with force expenditure, sports with strong manual loading.The manual training status was ranked by informations about manual loading at work and during leisure activities.The participants subjectively grouped themselves into the following four categories:2 (millimetre) in size. For the current test series, two different cylinder sizes were used, the smaller measuring 150 mm in circumference with a diameter of 48 mm, the bigger measuring 200 mm circumference and a diameter of 64 mm. The 150-mm cylinder records signals from 672 sensors and the 200-mm cylinder records signals from 896 sensors. Each sensor is calibrated to a maximum pressure of 600 kPa with a measurement error of < 5%. The sensors transmit their signals with a frequency of 20 Hz to the manugraphy analysis computer that is wired to the device. During the measurement the dynamics of the force distribution of the hand are displayed on a monitor. The force component vertical to the surface is calculated by the software separately for each sensor so that the force distribution across the different areas of the hand can be determined. The sum across all sensors gives the overall force, which is displayed as a force over time-diagram in newton (N). The force exerted on each individual sensor is colour coded and reported as a numerical value. The sensitivity threshold was set at 5 kPa so that the threshold per sensor is 0.25 N. During the measurement, the software determines the average force applied to the cylinder surface occupied by the examined hand. The measured pressure values of all those pressure sensors to which more pressure is applied than the previously calibrated air pressure is summed up. For better visualization a dynamic representation of the measuring foil in the form of a handprint can be deducted. The reliability of the manugraphy sytem is high with r > 0,97 [The novel® manugraphy system  is available with different sized cylinders that are enclosed in soft elastic pressure recording mats. Two calibrated pressure sensors per square centimetre are embedded in the mat. Each sensor element is 7.07 × 7.07mmr > 0,97 .N = 1 kg × 9.81 m/s2) so that the values can be compared to the manugraphy data. The Jamar dynamometer has been shown to produce measurements with a high intra-rater and inter-rater reliability. Manual reading errors are avoided by the use of the computer connected tool [The G200 Biometrics measuring device  is a modified digital Jamar dynamometer with a reliability of r > 0,98 –7. The cted tool –8.The individuals were examined by one investigator per centre using a standardised protocol. Prior to inclusion in the study a written declaration of informed consent was obtained from the study participants after the issues and risks associated with participating in the test were explained. The study protocol corresponds to the specifications in the Declaration of Helsinki and was checked and approved prior to the start of the study by the relevant ethics committee.Each participant was examined over three weeks on three different days with at least 24 h between each appointment. Half the tests were started with the measurement using the manugraphy system and the other half were started with the Jamar dynamometer and the order was changed over for each participant at the next visit. The initial choice was determined randomly.To minimise any influence due to the investigator, throughout both measurement procedures the subjects were accompanied by an automated voice that told the subjects to compress the measuring device for 5 s with maximum strength and then to rest for 10 s without releasing the device from the hand or changing the position of the hand on the device. This sequence could be transferred to a clinical setting as it is neither too time consuming nor too complicated. Three measurements were carried out with each device at every visit, starting with the left hand and then the right hand. Based on the recommendations of the American Society of Hand Therapists, the test participants sat on a stool without a back or arm rests with the upper arm resting on the upper body and with the shoulder in a neutral position and the elbow held at an angle of 90° . The wriThe subjects were not able to see the recording of the force curve on the PC monitor during the test to exclude any possible influence . The meaAll data were saved and analysed using the Windows® based statistical software package for the social sciences SPSS . In the first step, a descriptive analysis was carried out. The quantitative characteristics were described using the mean . As requested by the test-protocol there was a balanced sex distribution . The hands were classified as small in 53 (34.9%), medium in 53 (34.9%) and large in 46 (30.3%) of the subjects examined. For male participants average hand length accounted for 18.6 cm in comparison to an average hand length of 17.0 cm for the female participants.For each measuring system the maximum force and the mean force of the dominant and non-dominant hand were compared for both measuring steps (small handle and large handle, small and large grip position, respectively. This yields 8 parameters per measuring device for each potential influential factor.When measuring with the manugraphy system, significant differences were observed for the small and the large cylinder between the two sexes for all 8 parameters. The 76 men examined exerted significantly larger maximum and mean forces with both their dominant and non-dominant hand compared to the 76 women examined. Similar results were obtained for the Biometrics system Table –d.Table Hand length proved to have a significant influence on the hand strength.With the manugraphy system, the strength values for the 8 parameters increased from 26.3 to 74.5 N per centimetre of increase in hand length. For the Biometrics system, strength increased from 14.32 to 17.27 N when hand length increased by one centimetre Table +b.Table The differences between small and large hands amounted to 45–51% with the manugraphy system, whereas the participants with large hands exerted grip forces greater by 30–36% than the individuals with small hands measured with the Biometrics system. Additionally, the correlation coefficients showed that the hand length has a greater influence for the manugraphy system than for the Biometrics system.The participants were asked to subjectively assess their training status regarding occupational and leasure activities. According to the self-assessment, they were assigned to a specific group with 4 different training states. A significant difference between the maximum and mean strengths could not be confirmed for any of the 8 parameters neither for the manugraphy system nor the Biometrics system between the 4 groups when considering different manual loading of the hands Fig. .Fig. 3BoA statistically significant difference between the dominant and non-dominant hand could not be determined depending on the training status.Differences between the two study centers could not be observed proving the confirmability and stability of the measuring devices , 14. In Measuring grip strength with the Jamar dynamometer is an established and valid method that is often used in studies and routine clinical practice. It is easy to use and reproducible results are achieved , 5–7, 14In accordance with existing literature, this study verified that sex has an influence on hand strength –30. It iHand strength is clearly dependent on hand length and this also varies between the sexes. Men generally have larger hands , 29, 32.What speaks against this hypothesis is that in this test series the training status had no significant influence on the values of maximum and mean strengths. Repetitive manual loading at work or during leisure activities did not lead to significantly greater hand strength. This does not contradict the assumption that not using a hand leads to a reduction in strength , 33, 34.The differences in mean and maximum resultant forces between small and large hands were increased when measured with the manugraphy system. Partial explanation for this finding is that the finger tips do not touch the Jamar dynamometer during grip and therefore cannot take part in load transmission. Overall the values obtained with the manugraphy system were 45–100% higher than those measured with the Biometrics system, indicating that the manugraphy system provides higher sensitivity so that the exertion of the test participant during cylindrical grip is reflected more precisely.Strength of the study is that the test-retest reliability is even higher than indicated in the literature. This speaks for the precision of the measurement technology and the constant measurement circumstances provided by an accurate test-protocol. The manugraphy system is much more complicated and time-consuming to use, so it will certainly not replace the Jamar in everyday clinical practice. There is an abundance of data collected with each measurement cycle, making it difficult to interpret the results. Clear weakness of the study is the purely subjective assessment of the training status of the hand and the participant himself, so that the results based on the assumptions can only be used with reservation.The Jamar-dynamometer only measures grip force globally. Big advantage of the manugraphy system is that the measuring device is based on the sum of forces distributed over the surface of a cylinder and therefore allows for differentiated measurement even with low impact forces. It can provide a good resolution for localized pathologies and offers the perspective to better understand the biomechanics of the impaired hand. Hand strength is significantly influenced by sex and hand length. These factors should be taken into account in scientific publications that include measurements of hand strength as a comparative parameter in terms of the outcome of a treatment method. What appears to be important is that standard values for grip strength cannot be established. The comparison between the injured hand and the contralateral hand is of greater importance than the comparison to a normative collective. The manugraphy system provides similarly stable values, shows the same influencing factors and is similarly robust against potential confounders as the well-established Jamar dynamometer technique. As a recently introduced method for determining grip strength with defined local resolution, the device encourages further clinical studies on changes of force distribution in special disease patterns of the hand.


Online social networks have increasing influence on our society, they may play decisive roles in politics and can be crucial for the fate of companies. Such services compete with each other and some may even break down rapidly. Using social network datasets we show the main factors leading to such a dramatic collapse. At early stage mostly the loosely bound users disappear, later collective effects play the main role leading to cascading failures. We present a theory based on a generalised threshold model to explain the findings and show how the collapse time can be estimated in advance using the dynamics of the churning users. Our results shed light to possible mechanisms of instabilities in other competing social processes. Much less effort has been devoted to the understanding of the complex process of the decline of networks5. In this context the effect of random failures and intentional attacks9 has been investigated and recently the enhanced vulnerability and cascading breakdown of interdependent networks10 or k-core percolation11 were shown. The disintegration of real networks is usually a consequence of an interplay between endogenous and exogenous factors and its understanding is of major interest for a series of important questions like the decay of living organisms, the disintegration of social networks or the loss of market share in economic competition.Growth as a main route to the formation of complex networks have been studied in great detail13 like adoption of opinions, behavioural patterns, emotions17 or innovations can be considered as growth of a network of adopters on the top of an underlying network namely that of social interactions. Under some circumstances this process is surprisingly rapid. Social pressure plays a pivotal role in this context: People are influenced in their decisions by the opinions of their peers15. This effect is captured in the so called threshold models20, which assume that a person becomes adopter, when the ratio of her already adopting, related peers have reached a critical level characteristic to her sensitivity.Social contagion27 and has lead to a deeper understanding of how adopter networks emerge due to complex social contagion32. However, there can be an opposite process, when people forming a network of users of some technology or service leave this network. The reason can be getting uninterested in the service or churning to another provider33. Are there collective effects in this process as well, with the possibility of a dramatic collapse of the entire adopter network? The first aim of our paper is to use the data to show that this can indeed be the case and to present a model, which is able to describe the time dependence of the decomposition of such a networks. The second aim of this paper is to verify the model if it is able to predict in advance the collapse of a site.The above spreading processes are constructive in the sense that as a result a network of adopters emerges. The study of such processes have been boosted by the abundance of information communication datahttps://facebook.com) a particularly keen competition has developed among Online Social Networks (OSN-s) resulting in the defeat of a number of earlier popular sites. We will focus in this study data on iWiW34, which used to be the most successful Hungarian OSN. Results will also be shown for a much smaller OSN the Gowalla available from Large Stanford Dataset Collection35.After the success of Facebook .Here we present results for iWiWThe nodes of the network are the users of the service and links are the mutually acknowledged connections (“friendships”). Fig. Figure Around the end of 2010 the number of users leaving iWiW started to accelerate, which turned into a dramatic loss and lead finally to the collapse of the entire OSN. The turning point in the history of iWiW can be seen on the Google trends Fig.  where thrend of the active acquaintances of a user at the time of her last login with a week overhead. The results about the distribution of rend are shown in Fig. In order to study the above question we calculated the fraction k of friends of the users. While the distribution is for all k-values smooth and spreads over almost the whole range of rend, the position of the maximum jumps from ~0.9 for k < 130 to 0.4−0.5 for k ≥ 130 (see Supporting information for more details). This indicates the following mechanism: For all k values there are persons, who leave the OSN just due to the exogenous input–those, who have an active friend ratio close to 1 are certainly such users as they have not been influenced by the churning of their friends. Then, there are persons, who leave, when a considerable part of their partners have left. We can expect that the level of embeddedness into the OSN as measured by the number of friends has an impact on which of these factors is dominant. The users with the maximum close to 1 are mainly those with low embeddedness in (or affinity to37) the service as they have only relatively low number of friends in the OSN. On the other hand users with high affinity have many friends on the OSN, and they stick to the service as long as they can reach a good fraction of their friends. The data suggests that for the latter group the maximum of the distribution of active friends at the time of churning is around 45%. In the early period (mid 2007–end 2010) churning was mainly due to independent decisions triggered by some exogenous input or loss of interest. The deviation from the smooth, linearly increasing rate indicates the appearance of the collective effects.The distribution of the fraction of active friends at the time of last login depends in a specific way on the number The mechanism of the sharp transition from one position of the maximum to the other one can be understood such that the broad distributions result from two main processes: One with a maximum close to 1 and the other at around 0.5 and the weights of these get shifted from the former to the latter one as the degree increases see Fig. .32, which gives inspiration to modelling our empirical findings.The existence of thresholds in the decision to leave the service may lead to collective phenomena of avalanches or cascades. Indeed, we find such cascades in the data; for an example see Fig. nw1, nw2, nw4 respectively). Since apart from a constant shift no important difference was found between these quantities only nw1 is plotted in Fig. nw1 ≈ 2 10−4, when the OSN is at its best. Beginning late 2010 nw1 starts to increase rapidly and finally it shoots up at early 2013, which can be described as a power law with an exponent as (tc − t)−1.25 with tc = February 2013  but the ones who stayed for a while remained almost to the end of the site. The match by a factor of two between 12.2012 and 12.2011 indicates that the activity period was not a prime reason for staying or leaving at the end, the collective motion indicated by the peak in In the following we construct a model for the collapse of OSN-s, which incorporates both exogenous and collective effects on churning. The parameters of the model will be adjusted to the iWiW data.40. Finally we have a random network with N nodes and an average degree of 〈k〉. At the beginning all nodes are part of the OSN. In the Supplementary Information we present results using part of iWiW network as underlying structure.In order to keep the underlying structure simple, the model is defined on a random network where 40% of the links are created in an uncorrelated random way and the rest is generated by placing random triangles, as high clustering is typical for social networks41. It is natural to assume that only the set of closest friends matter in the decision of well embedded individuals about staying with the service or leaving it. Therefore we will consider only a network with reduced average degree, which is considered as a parameter.Social contacts have different intimacy levels building a hierarchy of concentric layers around the persons in their egocentric networks19: Whenever the fraction of active friends of a node drops below its threshold λ the node will feel inclined to leave the OSN. This does not happen immediately but with a rate 1/τ, so τ is the timescale of leaving the OSN after the threshold condition is fulfilled. All nodes are given a predefined uncorrelated threshold value λ = 0.5 ± 0.2 with uniform variations.For the endogenous, collective effects we implement a threshold mechanismγ = μt/τ, reflecting the growing interest in the competing service. We select nodes to leave the service with the probability which was a decreasing function of the node degree (see Supporting Information for details). This was motivated by the fact that more embedded users are more reluctant to leave the site due to exogenous effects.The spontaneous churning is defined as follows: At each timestep nodes leave the service with a rate linearly increasing with time: k〉 representing the friendship is created with all users begin member of the OSN.A network with average degree 〈t users leave with rate γ = μt/τ. (For the reproduction of k dependence of rend a k dependence in node selection may be introduced)At time λ are moved to the leaving queueUsers for which the ratio of the active friends dropped below the threshold τ. If this happens check all its friends for thresholdUsers in the leaving queue leave definitely with rate In summary the model is defined as follows:τ and 1/μ. The latter determines the exogenous timescale and can be fitted to the initial quadratic increase of the number of inactive agents, which relates the model time to real time, therefore it has no influence on the dynamics. The value of the threshold can be adjusted by measuring the peak in the rend curves.The dynamics defined this way has two timescales: τ and 〈k〉. The timescale τ controls the speed of the collapse of the service together with the average degree of the original network. If either τ is small  of the network has a high average degree the collapse of the site is almost instantaneous. We found that either large waiting time or low degree is needed to recover the empirical results.We are left with two parameters: k〉 = 10 and τ = 14.5 days. Both values are realistic: First, it is natural to assume that people check back for two more weeks after they start getting motivated to leave the service. Second, it was already suggested in41 that people have a circle of intimacy of about 12–15 friends and relatives with whom they have regular communication; these are the relationships, which are particularly important for them. In Fig. k〉 = 200. It is clear visually that this is a worse fit. For more details see Supporting Information.Fitting our model to the empirical data gives a prefect match as shown in Fig. 42 therefore we have decided to use the users in one of the counties to simulate the model.Here we used an artificial random network for the model studies. Since the contact network is available from iWiW we may use part of it (the whole being too large for simulation) to study the model. It was shown that political borders inside Hungary are apparent through the contact networkWe have introduced a probability with which the links are kept in order to be able to decrease the degree of the network. After decimating the links we remove nodes with degree 0 and 1. We have studied the evolution of the active users and the results is shown in Fig. In Fig. A further verification of the model besides Fig. We have also calculated the average number of churning users as function of the elapsed time. The results match well with the empirical data as shown in Fig. We studied the collapse of an online social network both empirically and by modelling. The empirical results suggest that in the early stage users leave the OSN mostly because they are not anchored to it by a large number of friends, that means, they are not interested enough in online networking or they churn to a competing service. As time goes on, the latter effect seems to dominate resulting in a linearly increasing churning rate following the increasing popularity of the competitor. This erosion of the network due to exogenous influence has the effect that the social pressure becomes critical for an increasing number of active users, who then decide to leave, which leads to a cascading effect and finally, to the collapse of the OSN.32 of the Watts threshold model19 the most important new elements of our model are as follows: First, we have taken into account the endogenous influence by introducing spontaneous churning with a time dependent rate, reflecting the increasing interest in the competitor OSN. Second, we introduced a delay time τ between the fulfilment of the threshold criterion and the action under the social pressure. This realistic element was used as a fitting parameter in the model calculations.The endogenous and exogenous effects were incorporated in a threshold model, which could reasonably well reproduce the measured quantities of the empirical system. Starting from a recent generalisationThe spontaneous churning due to endogenous influence dominates the early phase of the OSN, however, gradually cascades occur and finally they become dominant. From that time any effort to damp spontaneous churning  is in vain. The apparent stability of the OSN was only due to the relatively large characteristic time for cascading users.We have found empirically and reproduced by the model that the number of churning neighbours of a churning user within a given time before the event behaves as a power law with a critical time , which can be considered as the collapse time of the service. Similar observations in other systems may be used to predict the date of collapse due to social pressure.36 it had 3.5 million active users in 2010, in a country with a population of 10 million (worldwide 13 million native speakers) and at that time about 60% Internet penetration38. The site started as a non-profit project in April 2002, however, it was purchased by a giant telecom company in 2006 and remained the leading social network site of Hungary for years; in fact, it was considered as a main driving force behind the speed up of Internet penetration in Hungary.The social network iWiW (4.3 million registered users) was started in 2002 and closed down June 2014. The data used for this study for the period of April 4, 2002–January 23, 2013 includes: date of registration, last login of each user and time stamped link creation information. Using this data we can reconstruct the whole life cycle of iWiW  week(s) before the last login date of the user.Supplementary movie was made as follows: Movie time goes proportional to real time, Yellow circles indicate the last login of a given user. An arrow is drawn if the head user leaves no later than a week after the last login of the user at the tail. Colour goes from red to light blur with elapsed time.Supplementary InformationSample cascade


The horses were assigned into three groups based on the given treatment: Group 1 was fed psyllium [1 g/kg body weight (BW)] daily at home for a minimum of 10 days (n = 57); Group 2 was treated once with psyllium or magnesium sulfate by nasogastric tubing followed by daily feeding of psyllium (1 g/kg BW) at home for a minimum of 10 days (n = 19), and Group 3 was treated by daily nasogastric tubing for 3–7 days with psyllium and/or magnesium sulfate (1 g of each/kg BW) (n = 170).Ingestion of geosediment (further referred as sand) may cause weight loss, diarrhea and acute or recurrent colic in horses. Our aim was to compare the efficacy of three treatment protocols in clearing colonic sand accumulations in clinical patients. This retrospective clinical study consisted of 1097 horses and ponies, which were radiographed for the presence of colonic sand. Horses included to the study (n = 246) were displaying areas of sand in the radiographs of ≥75 cmThe initial area of sand did not differ significantly between the treatments. Group 3 had significantly less residual sand than Groups 1 and 2, and the proportion of resolved horses was higher in Group 3 than in Groups 1 and 2.Daily nasogastric tubing with psyllium and/or magnesium sulfate for 3–7 days removes large accumulations of sand from the colon in horses more effectively than feeding psyllium for at least 10 days. Ingestion of sand (geosediment) may cause serious, potentially life-threatening disease in horses living in areas with sandy soils or kept in sand paddocks. Colonic accumulation of geosediment, further referred as sand, is a geographically specific problem –3. Sand Abdominal radiography is the most reliable method for detection of an intestinal sand, since it provides an objective measurement of both the height and length of the sand, which cannot be evaluated with other methods such as abdominal ultrasonography  or abdomPlantago ovata .Hospital treatment: daily nasogastric tubing for 3–7 days with psyllium and/or MgSOIn all, 246 horses fulfilled the inclusion criteria. They were further sorted into groups according to the type of treatment protocol, as follows:During their stay in the hospital, the horses were box-rested and hand-walked, or turned out into a concrete paddock with no access to sand. The owners of the horses were advised to prevent further sand ingestion at home, either by muzzling the horses or changing the feeding management and avoiding turnout in sand paddocks, if possible.U test using statistical software . The outcome of the treatment was recorded as resolved if the area of sand in the follow-up radiograph was less than 25 cm2 [P value of <0.05 was considered statistically significant.Since the data were not normally distributed, the differences between the treatments were analyzed with Kruskal–Wallis analysis of variance and the Mann–Whitney n 25 cm2 . PearsonThe main reasons for abdominal radiography being performed are listed in Table P = 0.103). Horses treated with daily nasogastric intubation had significantly less residual sand and the proportion of resolved horses was higher than that of horses fed psyllium at home , the exact area of sand could not be measured at the beginning of the study, due to the large sizes of the accumulations. Therefore, the size of the accumulation was estimated. In the control radiographs, the exact area could not be measured, for similar reasons, in 10 horses in Group 1 and 7 in Group 3. For example, in one horse radiographed on several occasions within a short period of time, on day 1 the size of the accumulation was 156 cmMost horses (63 %) presented between October and December. Of nine horses from Groups 1 and 2 that were diagnosed and treated between December and February, three were able to clear the sand with psyllium feeding.4 by daily nasogastric tubing in the hospital resolved the sand accumulations more effectively and probably in a shorter time period than did feeding psyllium at home. In this retrospective material, most of the horses treated with nasogastric tubing were administered both psyllium and MgSO4. The number of horses administered only psyllium or MgSO4 was too small to make any comparisons between these treatments. However, in a previous prospective study the authors have demonstrated that the combination of psyllium and magnesium sulphate is more effective than either of the compounds alone [In the present study, repeated administration of psyllium and/or MgSOds alone .More than half of the horses treated with nasogastric tubing where considered resolved within eight days, whereas less than one-third of the horses fed psyllium at home had resolved the sand in the control radiographs taken within 40 days. Although keeping the horse in the hospital for daily nasogastric intubation is costly, it is not only more efficient, but could eventually be more cost-effective than feeding psyllium at home, because the need for repeated radiological examinations and the delayed recovery increases the costs, as well as the risk of developing colic due to the accumulated sand. A single nasogastric intubation of psyllium in addition to further feeding of psyllium at home did not result in any additional benefit, compared with psyllium feeding only. However, the number of horses in this group was small and therefore the approximated 95 % confidence interval for the population median was wide.It has previously been demonstrated that radiography can be a useful tool for monitoring the removal of sand . InsteadEven though the most commonly used treatment protocols differed between the university teaching hospital and the private practice, no significant differences were detected in the areas of sand between the groups at the beginning. In some horses, the exact areas of sand could not be measured, due to the large sizes of the accumulations, because the margins were not entirely seen in the radiographs. This was evident both in the initial and follow-up radiographs. However, these difficulties in determining the exact size of some very large sand accumulations did not interfere with the evaluation of the outcome.In the present study, sand accumulation was diagnosed in horses suffering from acute colic as well as in horses with chronic problems, such as loose feces or water with feces, weight loss and poor performance, all of which have been associated with colonic sand accumulation –5. Some In the present study, there was some variation in the treatments used, including the specific medications used, their doses and the duration of the treatment. When horses were treated in the hospital (Clinic A), the most commonly used protocol was daily nasogastric tubing and evaluation of the outcome by radiographs for the first time after 4 days. The aim of treatment was to remove the majority of the sand, however the treatment was often discontinued prior to this occurring and horses with very large sand accumulations were not routinely treated with nasogastric intubation for more than 7 days to avoid nasal irritation and loss of patient compliance. This same practice has been previously reported . In ClinWhether horses treated at home were exposed to additional sand during the treatment remains unknown. Even though owners were instructed to prevent access to sand, it is unclear if these recommendations were followed or successful. In contrast, the hospitalized horses had no further access to sand. There is only anecdotal information available on how rapidly sand accumulates in the colon but reoccurrence of sand accumulation within 6 weeks has been reported . It was Some of the horses treated at home were diagnosed and treated between December and February, at which time the ground was frozen and covered with snow in northern Finland, where these horses lived. The authors considered it unlikely that the horses had access to sand at the time yet only three of these nine horses were able to clear the sand with psyllium feeding. In some patients, the radiographic area actually increased in size during the treatment period, even though there was apparently no access to sand. Most likely, sand from other parts of the colon was moving along and increasing the size of the accumulation as previously reported .The length of the treatment at home varied, and many horses continued to consume psyllium for several weeks, because sand accumulation persisted in the colon. The follow-up period for the present study was restricted to 40 days, but clinical follow-up continued for those horses in which sand accumulation did not resolve. There has been some concern that feeding psyllium for long periods could decrease its efficacy, since the colonic flora may become able to metabolize it in increasing amounts . In the The impact of possible changes in diet on the outcome could not be evaluated in the present study. It has been suggested that having enough hay (minimum 1.5 % body weight) in the diet would enhance sand clearance . NeverthIn the present study the occurrence of sand colic and other sand-associated diseases varied seasonally with most cases clustered at the end of the year suggesting that the most problematic time in our geographical region is after the pasture season but before the ground either freezes or becomes covered with snow. The thermal beginning of winter has varied over the years, which may explain the continuum of cases in some years until January. Weather conditions may be associated with sand eating but previous reports have come from different geographical areas than the present study .4 and/or psyllium for 3–7 days removes sand accumulations from the colon in horses more effectively than feeding psyllium at home for at least 10 days.This retrospective study suggests that daily nasogastric tubing in hospital with MgSO


The rate of cesarean delivery (CD) in Brazil has increased over the past 40 years. The CD rate in public services is three times above the World Health Organization recommended values. Among strategies to reduce CD, the most important is reduction of primary cesarean. This study aimed to describe factors associated with CD during labor in primiparous women with a single cephalic pregnancy assisted in the Brazilian Public Health System (SUS).This study is part of the Birth in Brazil survey, a national hospital-based study of 23,894 postpartum women and their newborns. The rate of CD in primiparous women was estimated. Univariate and multivariable logistic regression was performed to analyze factors associated with CD during labor in primiparous women with a single cephalic pregnancy, including estimation of crude and adjusted odds ratios and their respective 95 % confidence intervals.The analyzed data are related to the 2814 eligible primiparous women who had vaginal birth or CD during labor in SUS hospitals. In adjusted analyses, residing in the Southeast region was associated with lower CD during labor. Occurrence of clinical and obstetric conditions potentially related to obstetric emergencies before delivery, early admission with < 4 cm of dilatation, a decision late in pregnancy for CD, and the use of analgesia were associated with a greater risk for CD. Favorable advice for vaginal birth during antenatal care, induction of labor, and the use of any good practices during labor were protective factors for CD. The type of professional who attended birth was not significant in the final analyses, but bivariate analysis showed a higher use of good practices and a smaller proportion of epidural analgesia in women cared for by at least one nurse midwife.The CD rate in primiparous women in SUS in Brazil is extremely high and can compromise the health of these women and their newborns. Information and support for vaginal birth during antenatal care, avoiding early admission, and promoting the use of good practices during labor assistance can reduce unnecessary CD. Considering the experience of other countries, incorporation of nurse midwives in childbirth care may increase the use of good practices during labor.The online version of this article (doi:10.1186/s12978-016-0231-z) contains supplementary material, which is available to authorized users. In modern obstetrics, cesarean delivery (CD) as a safe form of birth is responsible for reducing maternal and neonatal mortality . HoweverThe CD rate in Brazil has increased in a steadily manner over the previous past 40 years, and from 38 % in 2000 to 50.6 % in 2009 when this surgery became the main mode of delivery in the country .In Brazil, although the CD rate in private hospitals is the highest, in public services, it is approximately three times above the recommended rate . The BraThe obstetric model of care delivery has been identified as one of the causes for the increase in CD rate –10. In BIn primiparous, whose labor and delivery tend to be longer, the occurrence of CD and other maternal and perinatal outcomes is directly related to the quality of care. A study by Leal et al.  showed tThe objective of this study was to estimate the rate of elective and intrapartum CD in primiparous women with a singleton pregnancy and a fetus in the vertex presentation assisted in the Brazilian Public Health System (SUS) and describe the factors associated with CD during labor and childbirth care.This study is part of the Birth in Brazil survey, a national hospital-based study of a sample of postpartum women and their newborns that was conducted between February 2011 and October 2012. Hospitals with 500 or more annual deliveries were selected and stratified according to region, location , and type of healthcare . A total of 23,894 postpartum women were interviewed in 266 hospitals that were distributed in all Brazilian states. Further details regarding the sample design have been reported by Vasconcellos et al. . In the Data from primiparous women who had a single birth with the fetus in cephalic presentation born alive, or as a stillbirth after 22 weeks of pregnancy and assisted in the SUS were analyzed. Women who self-reported as “East Asian” or indigenous were excluded because of the small proportion of these participants in the sample . Univariate and unconditional multivariable logistic regression analysis of factors associated with intrapartum CD in primiparous women who were assisted in the SUS were made using a theoretical model with three levels of hierarchy  Univariate analysis was used to estimate the unadjusted odds ratio (OR) and 95 % confidence interval (95 % CI). In the first multivariable model, all distal variables were included. Variables of the distal level with a significance level estimated as lower than 0.20 were included in the second model, which also included all of the variables of the intermediate level. In the third model, distal and intermediate variables with a significance level estimated as lower than 0.20 and the proximal variables were included. All variables with a significance level of <0.05 and some variables of interest according to the theoretical model were retained in the final multivariable model. The results from the final multivariable model are expressed as adjusted ORs with their corresponding 95 % CIs.To analyze the association of the use of good practices during labor and the use of spinal or epidural analgesia with the professional who assisted labor, the chi-square test was used to determine differences between proportions with a significance level of <0.05.In all of the statistical analyses, the complex sampling design was taken into consideration. Data weighting was calculated according to the inverse of the probability of inclusion of each puerperal woman in the sample. To ensure that the distribution of puerperal women who were interviewed was similar to that observed among the births in the population sampled in 2011, a calibration procedure was used in each selection stratum . The weiAnalyses were performed using IBM SPSS software version 20.0 .This study was approved by the Research Ethics Committee of ENSP/Fiocruz, under report no. 92/2010. Care was taken to ensure privacy and confidentiality regarding the information collected from the women. Informed consent was obtained before the interview through the use of a informed consent statement.From the 23,894 women interviewed in the Birth in Brazil survey, 9838 (41.2 %) were attended in SUS hospitals. From a total of 4298 primiparous women who delivered in SUS hospitals 4079  had a single pregnancy with cephalic presentation. Of these, 1592 (39 %) underwent CD, most of the surgeries  occurred before onset of labor and 131 (3.2 %) had an indication for CD at the moment of admission to hospital. The number of primiparous women with a single cephalic gestation who had an indication for CD during labor was 327 . The analyzed data are related to the 2814 primiparous women with a singleton pregnancy and a fetus in cephalic presentation who had vaginal birth or CD during labor in SUS hospitals. Figure Almost half  of the respondents were up to 19 years old, 51 % were between 20 and 34 years and only 1 % were 35 years or older. The majority (65.2 %) of women self-reported their skin color as brown, had up to 8 years of education (58.1 %), lived with a partner (71.9 %), and had no paid work (73.7 %). Most primiparous women lived in the Northeast region (37.7 %) followed by the Southeast (36.6 %), the North (12.7 %), the South (6.7 %), and the Midwest (6.3 %).Almost all (99 %) primiparous women had had ANC, while only 7.2 % had their ANC considered appropriate when assessed according to the criteria proposed in the national protocol . Most , but we decided to keep this variable in the final model because of its relevance. In the bivariate analysis, women who had the presence of at least one midwife during labor had increased use of good practices and a smaller proportion of epidural analgesia Table . A higheThis study estimated the rate of elective (27.8 %) and intrapartum CD (8 %) in primiparous women with a singleton pregnancy and a fetus in the vertex presentation assisted in the public health services in Brazil. The total rate of 35.8 % is high when compared to studies with similar populations. Bryant et al.  found a Most of the CD in our study was elective but in this analysis, we have identified the factors associated with intrapartum CD. The occurrence of clinical and obstetric conditions potentially related to obstetric emergencies before delivery, a decision in late pregnancy for CD, early admission with < 4 cm of dilatation, and the use of analgesia were associated with a greater proportion of CD. Residing in southeast region, favorable advice for vaginal birth during antenatal care, induction of labor, and the use of any of the good practices during labor were protective factors for CD.Clinical and obstetric conditions are known risk factors for CD, both elective and intrapartum , 19. We Antenatal care is not only important for the adequate care of obstetric and clinical complications. Our results show that the receipt of information supportive of a vaginal birth and the decision to choose a vaginal birth at the end of pregnancy were associated with a lower rate of intrapartum CD. Domingues et al.  found thInduction of labor (IOL) was associated with a lower rate of intrapartum CD. This is a common procedure in different countries and can modify the maternal and perinatal outcomes . The ratEarly admission in labor with < 4 cm of dilation is a known risk for CD  and occuThe use of any of the good practices during labor was associated with lower rates of CD. In the Birth in Brazil study, Leal et al.  found a Restriction of oral intake may be unpleasant for some women, and may adversely influence their experience of labor. In a systematic review of randomized controlled trials and quasi-randomized controlled trials, Singata et al.  concludeLavender et al.  in a sysThere is evidence that walking and upright positions in the first stage reduces the duration of labor, the risk of CD and the need for epidural. In a systematic review, Lawrence et al found that women who were upright during labor were also less likely to have CD  and less likely to have an epidural  . Leal etAlmost 10 % of primiparous women in our study had an epidural during labor and its use was associated with an increase in the rate of CD. The effect of epidural analgesia on the CD rate in the literature is controversial. Eriksen et al.  found thThe type of professional who provided care during labor was not associated with intrapartum CD in the adjusted analysis. This result is contrary to those observed in studies conducted in different settings , 40, incIn our study, the presence of a nurse midwife was associated with increased use of good practices and less use of epidural analgesia, both conditions associated with a lower risk for CD. At a national level, only 18.7 % of primiparous women had access to a nurse midwife whilst being cared for labor. The highest rate was observed in the Southeast, the region that also presented the lowest rate of CD in the country. While future studies are necessary to confirm this hypothesis, it is possible that one explanation for the low rate of CD in the Southeast region is the significantly greater presence of a nurse midwife during labor care in SUS services located in this region. One study conducted in a health service located in this region  demonstrSocial and demographic factors were not associated with intrapartum CD. Although we didn’t identify age as a risk factor for intrapartum CD, it is noteworthy that almost half of the primiparous women in our study were younger than 20 years. In the USA, in 2012, only 2.5 % of primiparous women were adolescent . In a coThis is the first national Brazilian study that has assessed labor and birth care with a sampling process that allows estimates for all macro-regions, location of service  and type of service . However, this study has some limitations. First, we conducted the study in institutions with more than 500 deliveries each year, which are responsible for almost 80 % of all deliveries . The resThe rate of CD in primiparous women in the public health services in Brazil is extremely high. Strategies for reducing the rate of CD and interventions in childbirth should focus on primiparous women as a priority. Reducing and adequately managing clinical and obstetric complications, counseling primiparous women on the advantages of a vaginal birth and supporting their decision for a vaginal birth can help to reduce this rate. Avoiding early admission, promoting the use of best practices during assistance with labor, inducing labor when indicated, and the judicious use of epidural analgesia when indicated can also reduce unnecessary intrapartum CD. Further research is necessary to determine the effects of labor care provided by a nurse midwife on the rates of intrapartum CD.


The long‐term constancy checked over a period of nine months was less than ±0.6% for measurements, taking into account the angular response of the ionization chambers. No significant effect of the background radiation levels was observed on the measurements.The use of a radioactive check device containing Strontium 90 was investigated to carry out the redundancy checks of Farmer‐type ionization chambers. It was not possible to meet the recommended tolerance limits of the redundancy checks without taking into account the angular response of the ionization chambers. The ionization chambers exhibited a maximum variation of 1% in the angular response in this check device. After accounting for the angular response the maximum variation of the short‐term repeatability was 0.14% with a standard deviation of PACS number(s): 87.53.–j, 87.52.–g The device has an approximate 7‐cm‐deep channel to accommodate a Farmer‐type ion chamber. The diameter of the channel is fixed and is sufficient to accommodate snugly an ionization chamber with a maximum outer diameter of 8.6 mm. When the device is not in use, the channel is covered by a self‐shutting, spring‐loaded, protective lid. There is a second channel in the check device to accommodate a thermometer to measure temperature close to the point of measurement. The device weighs less than 10 kg.The fixed‐geometry check device used in this study was manufactured by the Nuclear Enterprises Ltd., Reading, England. A photographic picture of the device is shown in Fig. The ion chambers used in these investigations were two fully guarded PR‐06G and four unguarded PR‐06C ion chambers manufactured by Capintec Inc., Pittsburgh, PA. The PR‐06G ion chambers were connected to a PTW Unidos Universal Dosemeter . The PR‐06C ion chambers were each connected to a Capintec Model 192 Exposure meter . The PTW Unidos measured the ionization charge collected in coulombs (C) and the Capintec Exposure meters provided readings in arbitrary units of “mR.” Both types of ion chambers have similar structural design. The outer diameter of these ion chambers at the distal end was 7 mm, to a length of 2.4 cm, gradually increasing to a maximum of 8.6 mm. Due to this gradual increase in the diameter, these ion chambers fit quite snugly and reproducibly in the channel of the check device. It took about 45 seconds to collect a charge of 1 nC, in this check device.±0.3% for short‐term repeatability of redundancy check measurements as recommended by the IEC,The short‐term repeatability measurements were performed as described by the IEC.10×10 cm2 field size at depths of 10 cm and dmax in a water phantom with a source to axis distance of 100 cm. As shown in Fig. As shown in this figure, there are some differences between the characteristic angular response curves of the guarded and unguarded ion chambers. The difference between the characteristic shapes of the angular response curves of these two types of ion chambers with otherwise similar structural design is due to the somewhat asymmetric shape of the guard electrode, as pointed out by the manufacturer. As shown here, the ion chambers demonstrated a maximum variation of about 1% in angular response in the check device using a Strontium 90 source. An anisotropy in the angular response of cylindrical chambers is usually due to an eccentricity of the central electrode or a marked nonuniformity of the wall thickness.±0.05% (for ten measurements). The short‐term repeatability measured this way is well within the limits of ±0.3% as recommended by the IEC.Because of this anisotropic angular response exhibited by these ion chambers in this check device the short‐term repeatability measurements were then made by aligning a point on the ion chambers with a fixed point on the check device. The maximum variation of the short‐term reproducibility measurements was 0.14% with a standard deviation σ of The long‐term reproducibility measurements were made by two methods. In the first method, a point marked on the ion chamber was always aligned with a fixed point marked on the check device. In the second method, the measurements were made by inserting an ion chamber in a random angular orientation without aligning a point on the ion chamber with a fixed point on the check device. The measurements were then performed by successively rotating the ion chamber by 90 degrees, three times, relative to the initial random position. The measurements taken this way at four angular positions, 90 degrees apart, were then averaged. The measurements taken using the second method check an ion chamber from all axial directions and are free from procedural errors such as a loss of the mark on the ion chamber, over a long period of time. The long‐term reproducibility measurements were repeated at least twice a month for eight months over a total time span of nine months. We missed the measurements for a month during this period. The long‐term constancy measurements were corrected for temperature and pressure as well as for the decay of the Strontium 90 radioisotope. The results of long‐term reproducibility for a fully guarded (PR‐06G) ion chamber are shown in Fig. ±0.6% and is within the limits of ±0.7%, as recommended for such ion chambers and a check device.,The maximum variation of the long‐term reproducibility is less than In order to check the effect of scattered radiation from nearby objects surrounding the check device, the measurements were made by surrounding the check device using two 4‐cm‐thick lead bricks. The measurements that were made with and without the lead bricks surrounding the check device did not show any significant difference. This results from Strontium 90 being a pure beta emitter producing very small leakage effects. The exposure rate at the surface of the device is less than 7.5 μSv/hr. As the radiation source in this check device is placed very close to the measuring channel, only backscattered radiations scattering through 180 degrees will be able to enter the sensitive volume of an ionization chamber in the device. Considering about 80% attenuation of the backscattered radiations in the shielding walls of this device, the background radiation levels entering the measuring channel will be at 1.3 mR/min. These background radiation levels will produce a signal of about 0.24 pC in a Farmer‐type ionization chamber with a sensitive volume of 0.6 cc. This background signal is much smaller than a typical signal of 1.33 nC/min observed for these ionization chambers in this check device.We found the use of a radioactive check device for redundancy checks of our ion chambers quite user friendly. Due to its easy transportability and no significant effect of surrounding objects on the measurements, it is possible to carry out the redundancy checks of the ion chambers in treatment rooms where some of our ion chambers are permanently located for daily output checks. It is, however, important to take into account the effect of the angular response exhibited by the cylindrical ion chambers in this check device in order to meet the recommended limits for these tests. The recommended limits for the short‐term repeatability and long‐term reproducibility can be met by always inserting an ion chamber in the check device with the same orientation. The limits for the long‐term reproducibility can also be met by taking measurements at four rotation angles, 90 degrees apart, from an initial random position, and averaging the readings. The latter method has the advantage of checking an ion chamber from all axial directions.The authors would like to thank Dr. Douglas Cormack and Dr. William Ziegler for many useful discussions.


The aim of this study was to provide a framework to evaluate bibliometric indicators as decision support tools from a decision making perspective and to examine the information value of early career publication rate as a predictor of future productivity. We used ROC analysis to evaluate a bibliometric indicator as a tool for binary decision making. The dataset consisted of 451 early career researchers in the mathematical sub-field of number theory. We investigated the effect of three different definitions of top performance groups—top 10, top 25, and top 50 %; the consequences of using different thresholds in the prediction models; and the added prediction value of information on early career research collaboration and publications in prestige journals. We conclude that early career performance productivity has an information value in all tested decision scenarios, but future performance is more predictable if the definition of a high performance group is more exclusive. Estimated optimal decision thresholds using the Youden index indicated that the top 10 % decision scenario should use 7 articles, the top 25 % scenario should use 7 articles, and the top 50 % should use 5 articles to minimize prediction errors. A comparative analysis between the decision thresholds provided by the Youden index which take consequences into consideration and a method commonly used in evaluative bibliometrics which do not take consequences into consideration when determining decision thresholds, indicated that differences are trivial for the top 25 and the 50 % groups. However, a statistically significant difference between the methods was found for the top 10 % group. Information on early career collaboration and publication strategies did not add any prediction value to the bibliometric indicator publication rate in any of the models. The key contributions of this research is the focus on consequences in terms of prediction errors and the notion of transforming uncertainty into risk when we are choosing decision thresholds in bibliometricly informed decision making. The significance of our results are discussed from the point of view of a science policy and management. Active research policy strategies, especially policies that emphasize excellence, need to develop models for evaluation to prioritize and concentrate limited resources. In such models bibliometric indicators are increasingly used as tools for identify universities, research groups, and researchers that can be said to be “excellent”, and allocating research funding  as a predictor of future productivity from a decision making perspective. Our dataset consisted of 451 early career researchers in the mathematical sub-field of number theory. The purpose was twofold: (1) to provide an analytical framework that can be used to examine and evaluate bibliometric indicators as decision support tools; and (2) to gain knowledge of the potential consequences, in terms of costs and benefits, of using early career productivity as a predictor of future productivity in number theory from the point of view of decision making. We focus on productivity since productivity is an important dimension of research performance that can be quantified with bibliometric indicators ?If we want predict who will belong to a future top performance group on the basis of past productivity, we need to find a definition of a top performance group. There is no standard for defining a top performer in terms of productivity in the literature , between decision thresholds that are determined by the simple method, and decision thresholds that are optimized with a prediction model that take the cost of prediction errors into consideration?We also compare two methods for determining decision thresholds in a selection process. One method based on the assumption that if a researcher belong in a top performance group, e.g. the top 10 % group, in a past time period, he or she will belong to that top performance group in a future time period as well. We define this method as the simple method. In the second method the decision thresholds are based on a prediction model where consequences are analyzed in order to determine an “optimal” decision threshold. Our second research question can be formulated as:3.How do publications in prestige journals and collaboration early in the career affect prediction accuracy and prediction errors ?Early career productivity can be affected by factors such as collaboration and publication strategies. This motivates an examination of the consequences of adding predictors to the prediction models. Our third research question can be formulated as:Our data was collected from the MathSciNet (MSN) database, a comprehensive mathematics database with a global coverage provided by American Mathematical Society. The MSN database has two features that make it suitable for bibliometric analysis at the individual level. First, the problem with author name ambiguities  was the 50th percentile, the threshold for the top 25 % group in period 2 was the 75th percentile, and the threshold for top 10 % group was the 90th percentile. We used the publication output of the 451 authors in period 2 as a reference set to calculate the percentiles , to delineate prestige journal publications in mathematics. We downloaded an excel file from CWTS Journal Indicators that contained a list of all journals indexed in the Scopus database between 1999 and 2014 CWTS . The CWTA prestige journal was defined as a journal with a SNIP value ≥ the 75th percentile based on a ranking of all journals included in the CWTS Journal Indicators list CWTS . We calcThe second covariate address early career collaboration. Collaboration is often controlled for in evaluative bibliometrics. Hu et al.  found a The basic model used in the univariate ROC analysis is the confusion matrix Table . The conCross tabulation of the test outcome versus the actual state classifies the population into four categories. Researchers for which the test indicated a positive value can either be classified as true positives (TP) if they belong to the specified performance group, or false positives (FP) if they do not belong to the specified performance group. Individuals for which the test outcome is negative can either be classified as false negatives (FN) if they belong to the specified performance group, or as true negatives (TN) if they do not belong to the specified performance group Fawcett . There aThe confusion matrix can be used to calculate several metrics that are important for examining the information value of a prediction model in terms of prediction accuracy and prediction errors. The true positive rate (TPR) is defined as TPR = TP/(TP + FN). The true positive rate denotes the fraction of researchers that are correctly classified as members in a specific top performance group and can be interpreted as an indication of the benefits of a binary prediction model. Synonyms for true positive rate is e.g., sensitivity, recall, hit rate and true positive fraction. The false positive rate (FPR) is defined as FPR = FP/(FP + TN). The false positive rate denotes the fraction of researchers that are misclassified as belonging to a specific top performance group, and can be interpreted as the costs of a binary prediction model. False positive rate is equivalent to the fall-out measure or false positive fraction, and are sometimes defined as 1-specificity. Specificity is equivalent to the true negative rate (TNR). The true negative rate is defined as TNR = TN/(TN + FP). True negative rate denotes the fraction of researchers that are correctly classified as not belonging in a specific top performance group. The false negative rate (FNR) is defined as FNR = FN/(FN + TP) and denotes the fraction of researchers that are misclassified as not belonging to a specific top performance group. The false negative rate is also known as miss rate. The metrics, true positive rate, false positive rate, true negative rate, false negative rate, are actually not rates, but probabilities or fractions Pepe . These fThe true positive rate can be interpreted as the conditional probability of being classified as positive given that one belongs to the top performance group (i.e. P(Positive|True)), and false positive rate can be interpreted as the conditional probability of being classified as positive given that one do not belong to the top performance group ). In an examination of the information value of early career publication rate as a predictor for future productivity it is also interesting to ask: What is the conditional probability for making a correct decision given that the test is positive (i.e. P(True|Positive)), and the conditional probability of making a correct decision when the test is negative )? These questions can be answered with the metrics positive predictive value (PPV) and negative predictive value (NPV). Positive predictive value can be defined as PPV = TP/(TP + FP). Negative predictive value can be defined as NPV = TN/(TN + FN). Positive predictive value and negative predictive value measure how well the test result predict the performance level of a researcher. Positive predictive value denotes the fraction correctly classified researchers of all researchers that tested Positive and negative predictive value denotes the fraction correctly classified researchers of all researchers that tested Negative. Positive predictive value and negative predictive value contain values between . On the contrary to true positive rate and false positive rate, predictive values are sensitive to skewed classes in the binary dependent variable Pepe .The ROC graph consists of a two-dimensional ROC space generated by the trade-off between the false positive rate  and the true positive rate  of a binary prediction model Fawcett . The falThe position of a point in ROC space represent particular features of the prediction model Fawcett . Some keIt is meaningful to partition ROC space in the positive diagonal. We define this line as the reference line Fig. . If the Many prediction models produce an estimate of a unit’s class membership as a probability, or a classification score, to which different thresholds may be applied to predict class membership Fawcett . For sucA ROC curve is generated by plotting the range of trade-offs between false positive rate and true positive rate that can be achieved by a given predictor  or prediction model. Conceptually, a ROC curve is generated in ROC space if we produce a confusion matrix, calculate the false positive rate and true positive rate, and plot the false positive rate against the true positive rate for every possible threshold of the probabilistic or classification score-based prediction model Fawcett . The dasA commonly used measure to summarize the performance of a ROC curve in terms of prediction accuracy is the area under the ROC curve Fawcett . The valWhen we are using publication track records to inform a decision making process we need to choose a cut-off value  of the test variable  that can be used as selection criteria so that each individual in the population can be classified as a member or non-member of a future top performance group. Generally the decision threshold is chosen on the basis of the acceptable trade-off between the false positive rate  and the true positive rate  given the circumstances of the decision situation Pepe .Method one is based on the assumption that if a researcher belongs in the top performance group in the first period he or she will belong in the top group in the second period as well. We define this as the simple method since we are using information solely from period 1 without taking the cost of prediction errors into consideration when determining the cut-off thresholds. The simple method represent the common practice when bibliometric indicators are used as decision support tools in science policy and management .X, and the new covariate, Y, and one model without Y:OR) denote the natural logarithm of the odds ratio of a positive outcome in Eqs.  of selecting for a particular top performance group in period 2 on the basis the bibliometric indicator publication rate in period 1 given different decision thresholds. In the second part we examine if and how prediction accuracy and prediction errors  are affected by adding covariates to the univariate ROC models in the three decision scenarios.Figure In the decision scenarios we used the observed values to compare different metrics, decision thresholds, and definitions of top performance groups. However, to get an indication of the stability of these observed values, if we were to repeat the analyses a large number of times, we used bootstrap resampling to estimate confidence intervals for the area under the ROC curves, the true positive rate and false positive rate of the decision thresholds, and the positive predictive values and negative predictive values  for the area under the ROC curve of each ROC curve Table . The conx  and y  directions . The true positive rate was 0.73, and the false positive rate was 0.47  at the Optimal method decision threshold for the top 50 % group  the true positive rate was 0.57, and the false positive rate was 0.19. The 90 % confidence region is identical as can be seen in Fig. At the Optimal method decision threshold the positive predictive value was 0.51 , and a more exclusive decision threshold of 11 articles compared to the Optimal method decision threshold at 7 articles  decision threshold and the Optimal method resulted in a more inclusive  decision threshold. A consequence of an inclusive decision threshold, compared to an exclusive threshold, is that more individuals are included in the selection. Thus, if we would use the Optimal method in a selection process where the top 10 % group is prioritized we would get less prediction errors compared to the Simple method. However, the inclusion of more individuals may be viewed as a cost that must be balanced against the benefit of reducing prediction errors.If we turn to the Simple method, we see that the true positive rate was very low and thus the false negative rate was very high, and as a consequence the Simple method would miss a large fraction of potential future top performing mathematicians see Fig. ; Table 4As can be seen in Table The positive predictive value for the Simple method decision threshold was 0.48 . Naturally the positive predictive value increase in a scenario where we use a more exclusive decision threshold . However, this assumption may not hold true. To asses whether or not a decision threshold actually is useful we need information on consequences. With the Optimal method we are analyzing the consequences of all decision thresholds in terms of prediction errors and can chose the decision threshold that is optimal according to the preferred outcome. The difference between the two methods can be represented by two concepts from decision theory: uncertainty and risk. A decision maker acts under uncertainty when the consequences of a decision is unknown . An advantage with this restriction is that all included authors share similar career trajectories  and the praxis in evaluative bibliometrics is to combine several complementary indicators Moed , we needOne of the key contributions of this research is the focus on consequences in terms of prediction errors and the notion of transforming uncertainty into risk when we are choosing decision thresholds. A future venue of research could revolve around the question of how to assign actual costs  to prediction errors in the context of bibliometricly informed decision making. The generalizability of our results may extend to other mathematical sub-fields oriented towards pure mathematics. Another useful line of research could be to apply the ROC framework to other fields with different publication practices compared to mathematics, such as physics, chemistry or medicine, where productivity to a larger extent is driven by, e.g., access to resources and collaboration. It would also be interesting to extend the ROC framework to other career phases, other dimensions of research performance and examine the added prediction value of covariates other than early career collaboration and publications in prestige journals.