LWTC) for the prevention of leptospirosis. The respondents pledged an average labor contribution of 10.66 h/month. The average LWTC corresponded to a monetary value of US$4.01 per month when valued using the opportunity cost of labor (leisure rate of time). From the monetized labor contribution, the total economic value of preventing leptospirosis was estimated at US$124.97 million per annum, which represents 1.13% of Metro Manila’s gross domestic product (GDP). Estimates from a Tobit regression model identified the respondents’ knowledge regarding leptospirosis, the susceptibility of their homes to flooding, and the proximity of their homes to sewers as significant factors to consider when developing resource contribution programs for leptospirosis prevention. More efforts need to be made in developing community level preventive programs, and in improving public’s knowledge and awareness about leptospirosis.Leptospirosis is a serious public health concern in the Philippines, not only because of its increasing incidence rate, but also because of its significant health and economic impacts. Despite its relatively high seroprevalence, knowledge on the economic burden of disease, particularly on the value that the society places on disease prevention remains limited. Obtaining such information is important within the context of public health policy. This study was conducted in Metro Manila to determine the economic burden of leptospirosis, by asking respondents about their willingness to contribute to labor ( Leptospira [Leptospirosis is a zoonotic infection caused by spirochetes belonging to pathogenic species of ptospira . Rodentsptospira . Human iptospira . The bacptospira ,4.Leptospirosis is considered endemic in the Philippines . The lepPoor sanitation and inadequate garbage disposal are major problems in Metro Manila. Estimates state that of the 6,700 tons of solid waste generated daily in Metro Manila, approximately 6,000 tons is either hauled to the city’s dumpsites or dumped illegally on private lands, in rivers, creeks, bay and vacant sections . UncolleLeptospirosis is a public health concern because its increasing incidence rate also imposes health and economic impacts on society. People infected with the disease do not only endure the physical and emotional pain of the illness, but they also have to contend with the financial costs of medical treatments combined with lost work or productivity. Urban slum dwellers often suffer the most during outbreaks because of their precarious living conditions, lack of access to health and sanitation infrastructures, and vulnerability to natural calamities . FurtherAside from a few serological and epidemiological studies on leptospirosis ,5,10, thWillingness to pay (WTP) is one method that can be used to measure the economic burden of diseases. It can be derived using a contingent valuation (CV) survey that elicits the maximum amount of money an individual is willing to pay to prevent undesirable health outcomes. The WTP approach is capable of measuring the intangible burden of disease such as pain and sufferings, which are not easily quantified using other valuation techniques . AlthougThe use of money as a payment vehicle in CV poses certain limitations, especially when applied within the context of developing countries where many transactions are partially monetized , labor mLWTC) approach. The use of the LWTC approach has particular significance in the study considering that the groups vulnerable to leptospirosis are those living in the poor urban communities of Metro Manila, where poverty incidence is high and unemployment prevails. Thus, using money as a payment vehicle in CV may prevent them from fully expressing their true appreciation of the proposed prevention program. Moreover, the valuation scenario requires the engagement of the respondents in the proposed activity of the leptospirosis prevention program. The factors affecting respondents’ LWTC for the prevention of leptospirosis are also presented in this paper.This paper describes the initial exploration of an on-going project related to the economic burden of disease in the Philippines. It represents the first attempt to measure the economic value of preventing leptospirosis among urban dwellers in Metro Manila using willingness to contribute in terms of labor  in the said area. The blood specimens of the respondents were tested for anti-Leptospira antibodies using an Enzyme-linked Immunosorbent Assay (ELISA). Likewise, information on the socio-demographics, knowledge and awareness about leptospirosis and home-environmental attributes of the selected respondents were also collected. The respondents were also provided with health information about leptospirosis after the data collection. At the end of the seroprevalence survey, a total of 839 individuals were identified seronegative in the ELISA. The 839 seronegative individuals were followed-up after a few months to determine the incidence of sero-conversion, however only 447 individuals representing 199 households agreed to participate in the second blood screening.The University of the Philippines-College of Public Health (UP-CPH) initially conducted a seroprevalence survey from October 2010 to January 2011 to determine the prevalence of leptospirosis in Metro Manila. Using a three-stage cluster sampling design, the seroprevalence survey collected blood specimens from 1,136 individuals representing 413 households across 30 Leptospira antibodies among the CV respondents was estimated at 24.38%. However, it should be noted that although these respondents had anti-Leptospira antibodies, they were all asymptomatic and did not have clinical manifestations of leptospirosis.The contingent valuation (CV) survey was conducted from May to June 2011. The CV survey was approved by the ethics committee of the UP-CPH as part of the burden of leptospirosis study. Based on the list of 199 households that participated in the sero-conversion screening, only one respondent per household was selected for the CV survey. The eligible respondents were those who agreed to participate in both the first and second blood screenings, and only those aged 15 or over in order to comply with the country’s law on legal working age. During field interviews in the CV survey, a higher response was generated among females probably because they usually stayed home to take full responsibility for housework. This situation reflects the characteristics of the seroprevalence survey, where the respondents for the CV survey were drawn. The prevalence of leptospirosis based on the detection of anti-barangay and health advocacy activities. The questionnaire was pretested to see how it works and to make necessary changes before the start of the actual survey.The CV questionnaire was developed after taking into account the inter-related problems of indiscriminate dumping of garbage, rat proliferation, and leptospirosis outbreaks in Metro Manila. The questionnaire contained a hypothetical leptospirosis prevention program that required the local community to participate and contribute some of their time in voluntary work for the prevention of leptospirosis. The tasks included environmental cleanup activities to eradicate rats in their respective The research staff of the UP-CPH conducted face-to-face interviews with the respondents. While respondents were likely to have already developed familiarity with leptospirosis considering that they had previously participated in the seroprevalence survey, the research staff still reminded them on the causes, clinical symptoms of infection and risk of acquiring leptospirosis prior to interview. The respondents were also informed about all aspects of the study and gave written informed consent. During the interviews, the respondents were presented with a detailed description of the goods being valued, and the method of their contributions. Using an open-ended CV format, the respondents were initially asked about the maximum amount of time that they would be willing to contribute in terms of voluntary labor to the proposed leptospirosis prevention program. The respondents were asked a further question at the end of the interview regarding their expected wages if they were to get paid for the voluntary work. The expected wage rate was used to calculate the opportunity cost of their labor contribution to the proposed program.In the analysis, the respondents’ responses to the CV questions were matched with their corresponding data taken from the previous seroprevalence survey, which includes: information on the socio-demographics of the respondents in both individual and household levels, respondents’ knowledge and awareness about leptospirosis and the environmental attributes of the respondents’ homes. Data regarding the flood susceptibility index was derived by plotting the residential address of each respondent on an interactive GIS of the flood and landslide susceptibility map for Metro Manila provided by the Mines and Geosciences Bureau . Data frAn individual’s WTP for goods and services is typically elicited in monetary units. However, recent studies have shown the plausibility of using labor contribution as a payment vehicle in CV surveys. For instance, labor contribution has been used to measure WTP for potable drinking water . Other sLWTC approach after taking into account the socio-economic characteristics of survey respondents. Many of the respondents live in Metro Manila’s poor urban communities, and they have incomes and resources that are often insufficient to meet the basic standard of living. In addition, in Metro Manila some workers’ wages are paid partly in money and the remainder in a non-monetary unit, for instance with food. The presence of tight income constraints and labor market imperfections could prevent individuals from fully expressing their true thoughts regarding the program when monetary payment is used to measure their WTP. Under these situations, a welfare measure that relies on monetary WTP may not only lead to the possible rejection of socially viable programs, but it may also undermine the potential contributions and concerns of low income societies.The present study adopted the The theoretical framework of using time as a payment vehicle for CV studies is based on the notion of a time-compensating surplus, which is analogous to a compensating surplus measure of monetary WTP . Based oV) denotes the amount of time a respondent is willing to contribute to labor (LWTC) for the proposed leptospirosis prevention program, and can be utilized to provide a change in environmental quality, from an environment prone to leptospirosis (0q) to an improved environment that is less prone to leptospirosis (1q). The labor time contribution to the proposed program represents a payment and involves a reduction in the respondents’ time budget (M) available for other activities (work or leisure). The variable (Z) represents the vectors of the socioeconomic variables that vary across the respondents.The indirect utility function wheLWTC values for the proposed leptospirosis prevention program, including auxiliary data regarding the respondents’ socioeconomic and environmental characteristics, were incorporated in the Tobit regression model. An empirical model was then derived for the determination of factors affecting LWTC for the prevention of leptospirosis. The empirical model is presented as:0, β1, …β7 are coefficients and ie is the normally distributed error term. The dependent and independent variables are defined in LWTC in a leptospirosis prevention program is determined by socio-economic factors related to the respondents’ age, gender, income, and knowledge about leptospirosis, as well the environmental characteristics of the respondents’ homes in terms of susceptibility to floods and proximity to sewers and waste dumpsites.The obtained LWTC into monetary value, the respondents were asked about their expected wage rate (pesos/hour) if they were to get paid for the voluntary labor. The expected wage rate was used to estimate the opportunity cost of time contribution for leptospirosis prevention program. The opportunity cost of time may vary considerably from one respondent to another, and depends on whether working time or leisure is to be allocated for labor contribution to the leptospirosis prevention program. If respondents are making trade-off between working time and time spent towards contributing to leptospirosis prevention, then the opportunity cost of time can be valued in a relatively straightforward manner using the average wage rate of time (WRT) as defined in Equation (5): represents willingness to contribute to labor for leptospirosis prevention by respondent i; iw represents the expected wage of respondent i; and n represents the total number of respondents in the sample. However, if leisure time is being substituted for time spent contributing to leptospirosis prevention, then the opportunity cost of time can be valued using the leisure rate of time. Based on the method developed by Cesario (1976) as cited in O’Garra (2009), the average leisure rate of time (LRT) is equivalent to a third of the value of the average wage rate of time [Respondents who did not accept the hypothetical scenario described in the CV survey were treated as having zero values, while respondents with positive responses had their labor contribution converted into monetary values. The assumption is that time to be spent in doing voluntary labor for leptospirosis prevention will require an opportunity cost, hence it has economic value. To covert  of time :(6)When respondents were asked about the amount of time they were willing to contribute for voluntary labor to the proposed leptospirosis prevention program, the results indicated a broad acceptance of labor as a payment vehicle. As shown in per annum based on the average wage rate of time. The average leisure rate of time, which represents a one-third value of the average wage rate of time, was estimated at 169.08 pesos (US$4.01) a month or 2,027 pesos (US$48.09) per annum. To further estimate the total benefit of preventing leptospirosis, the estimated annual opportunity cost of time (wage rate and leisure rate) was multiplied to the estimated 2,601,094 households living in Metro Manila [The opportunity cost of time that respondents are willing to contribute toward leptospirosis prevention was valued at 507.25 pesos (US$12.03) a month or 6,087 pesos (US$144.33) o Manila . A totalo Manila . To avoiLWTC for the prevention of leptospirosis. The regression model performed adequately with a chi-square value of 13.33, which was significant at a p-value of 0.05. The regression model identified KNOWLEDGE, FLOODPRONE, and SEWER as statistically significant factors affecting LWTC with p-values less than 0.10 and 0.05. The LWTC was positively associated with the respondent’s knowledge about leptospirosis and with respondents living in high-risk flood areas. In contrast, LWTC was negatively associated with respondents living near sewers. Other variables such as AGE, GENDER, INCOME, and WASTEDUMP were not statistically significant  in explaining the dependent variable.The number of leptospirosis outbreaks in Metro Manila has been directly attributed to socio-economic and environmental factors including unplanned urbanization and growth in urban slums, poor waste disposal, poor sanitation, rat infestation, heavy rains, and floods . It is eLWTC and KNOWLEDGE suggests that respondents with a higher knowledge regarding leptospirosis placed a higher value on disease prevention programs. This result is consistent with prior studies found in the literature. Pokou et al. found that willingness to contribute to labor for tsetse control in Africa is positively associated with individual’s knowledge about disease [et al. also confirmed that individuals with greater knowledge about dengue fever were more likely to engage in preventive measures than individuals with no knowledge [The study also gave a clear indication that respondents’ knowledge about leptospirosis, susceptibility of home to flooding, and proximity of home to sewers are significant determinants of willingness to contribute in terms of labor for the proposed leptospirosis prevention program. The positive association between  disease . Van Bennowledge . Thus, iIt should be noted that although more than half of the respondents (55%) demonstrated high levels of knowledge and awarness of the cause, mode of transmission, signs and symptoms, and ways to prevent leptospirosis; a substantial proportion of respondents (45%) demonstrated a moderate though inadequate level of knowledge about leptospirosis. Considering the importance of knowledge in disease prevention, this study supports the need to improve peoples’ knowledge via education and health promotion programs on leptospirosis.Leptospira antibodies is significantly associated with various environmental attributes including exposure to floods [FLOODPRONE and LWTC. Respondents living in Metro Manila’s high-risk flood areas were more willing to contribute greater hours to the prevention of leptospirosis because they probably perceived themselves to be at high risk of infection.Studies in the literature have associated flooding with numerous outbreaks of leptospirosis around the world ,33,34,35o floods . These fLWTC and SEWER (the proximity of homes to sewers). Contrary to our expectations, our finding showed that respondents living near sewers had lower LWTC values compared with those living far from sewers. There are possible explanations for this finding. First, we could relate this finding on the recent study that shows no statistically significant correlation between the seroprevalence of leptospirosis in Metro Manila and proximity homes to open sewers [Sewers often serve as habitats for rats. Rat urine and feces are likely to contaminate these sewers, thereby increasing the risk of disease exposure to nearby dwellers. Such a premise was considered in this study, which made us expect a positive association between n sewers . It is pn sewers ,39. Peopn sewers ,41. Tenun sewers . Hence, The willingness to pay (WTP) approach is becoming increasingly accepted in health economics to elicit utility values for health states. It poses certain advantages and disadvantages when compared with other health valuation methods. Unlike the adjusted life years (QALYs) and disability-adjusted life years (DALYs) methods, where health values are indexed on a 0 to1 scale of health , the WTPThis study attempted to use labor-time contribution as payment vehicle to WTP for disease prevention, and to monetize labor-time contribution using the opportunity cost of time in order to capture some of the limitations of monetary WTP approach within the context of low income households. Although results from this study reveal that our methodological approach ought to be considered when applying WTP in health valuation studies, further improvements are required to deal with several limitations.LWTC may just represent the value that poor urban dwellers in Metro Manila place on leptospirosis prevention considering that the CV respondents were mostly low-income earners. The value that high-income earners place on leptospirosis prevention is underrepresented in the study. Future work could compare the value of leptospirosis prevention and preference for labor contribution between high and low income earners in Metro Manila should be considered in future studies. This could be done through a wider randomized survey to include respondents within the high-income brackets of the metropolis.First, the average Second, the presence of zero responses is a relatively common observation in CV surveys. The proportion of zero responses can range from 24% to 60% ,47. AlthLWTC of an individual who had experienced leptospirosis might be higher when compared with someone who has no experience with disease. Hence, a comparison of the LWTC values between leptospirosis patients and non-patients may merit further research.Third, the economic value of disease prevention may vary based on the individual’s experience with the disease. It is possible that the LWTC given the presence of a number of zero responses and few high LWTC values (maximum 160 h/month). Open-ended elicitation format suffers from lack of incentive compatibility and may encourage respondents to free-ride [Fourth, the used of open-ended elicitation format in our study may have caused some variations in the values of ree-ride . The useree-ride ,49. It iFinally, this study did not take into account the substitution between labor and money contributions as payment vehicle for CVM. Future research might consider examining the determinants of willingness to contribute to the disease prevention in relation to the form of contributions, in particular money, labor or a mix of both.The main purpose of this study was to measure the economic welfare of preventing leptospirosis in an urban setting without reliance on the conventional contingent valuation method (CVM). Instead of asking for monetary payment, individuals were asked how much time they would be willing to contribute to the proposed leptospirosis prevention program. Such an approach is useful not only within the perspective of poor economies, but also in situations where community engagement is important for the successful implementation of development programs.per annum provides a solid ground for investment in preventive measures. Knowledge about leptospirosis, susceptibility of home to flooding, and proximity of home to sewers are key factors to consider when developing resource contribution programs for the prevention of leptospirosis. More efforts need to be made in developing community level preventive programs, and in improving the knowledge and awareness of the public about leptospirosis. Lastly, while the technique used in the study has certain limitations, it still affords a modest contribution to the limited literature on the economic burden of leptospirosis, and on the use contingent valuation method in valuing health program benefits within the context of developing countries.This study shows that CVM payment in the form of labor contribution was acceptable among the urban dwellers in Metro Manila. The importance of using this method becomes more apparent when time contributions are valued using the opportunity cost of labor. Using a leisure rate of time, the derived aggregate estimate of the total benefit of leptospirosis prevention valued at US$124.97 million


Heracleum mantegazzianum, persists at sites once colonized and how its ability to persist affects its distribution.As accurate and up-to-date distribution data for plant species are rarely available, cumulative records over long periods of time are frequently used for mapping distributions, without taking into account that species do not persist in their historical localities forever. However, persistence is highly relevant in changing modern landscapes, especially for invasive species that dynamically spread in unstable human-made habitats. We studied how an invasive species, The Czech Republic.H. mantegazzianum occurrence reported in the literature and herbaria to determine whether the species still occurs at these sites. By using G-tests and classification trees, we explored the roles of various factors affecting its persistence at a site.We visited 521 localities of Of the total number of 521 historical sites at which the species has occurred since the end of the 19th century, it persists at only 124 (23.8%). The persistence rate differs with respect to habitat type and is highest in meadows and forest margins. Analysis using classification trees indicated that the factors that best explain persistence are: type of habitat (with meadow and forest margins over-represented); urbanity (with a higher persistence outside urban areas); proximity to the place of the species’ introduction into the country; metapopulation connectivity; and distance to the nearest neighbouring population.H. mantegazzanium, which is non-clonal and reproduces only by seed, estimates of distribution and spread based on historical data are informative about potentially suitable habitat but may be unreliable as indicators of current occurrence and invasion dynamics.The use of cumulative historical records as a measure of species distribution, which is common in invasion literature, can seriously overestimate the actual distribution of alien plant species with low persistence. In the case of alien species such as  Invasion ecologists have long been interested in studying the colonization ability of alien species . Common Swertia perenis, Dryopteris cristata, Fallopia japonica, F. sachalinensis and Rudbeckia laciniata; Heracleum mantegazzianum in Ireland  is rarely acknowledged and has never been tested using rigorous data. What is largely neglected is that the mapped distribution may be smaller than reported or may differ from reality owing to local attrition and colonization. This is even more pronounced in the case of alien species, where most attention is paid to spread and dispersal processes over large distances , and at a historical temporal scale of up to 120 years. Detailed data on the invasion history of this species in the Czech Republic are available. However, it is unclear how population dynamics, human-mediated and natural long-distance dispersal events, and recent eradication efforts have affected its distribution over time. We ask the following questions. (1) How does the species persist in sites once colonized? (2) What are the ecological and human-related factors that determine whether the species persists in a site or not? (3) What is the actual current distribution of H. mantegazzianum and how does it differ from the distribution that can be derived from the historical literature? Finally, if it is different, (4) what implications could such bias have on our perception of the ecology, distribution and historical invasion dynamics of alien species?In this study, we explore the persistence of a monocarpic invasive species, Heracleum mantegazzianum Sommier & Levier (Apiaceae) is a monocarpic, short-lived perennial hemicryptophyte that reproduces exclusively by seed . Sites from the highly invaded region in western Bohemia, where the species was originally introduced to the Czech Republic . The historical distribution was taken from the list of records published in H. mantegazzianum at some point between 1877, which is the date of the first record of the species in the wild in the Czech Republic    were fouGeographical coordinates were obtained for each revised or newly recorded site using GPS, and the following characteristics were recorded in the field.riparian ; vicinity of roads; vicinity of paths; railway embankments and their vicinity; industrial sites in cities; public parks, including green areas and private gardens in cities and villages; orchards; disturbed ruderal sites in the landscape such as rubbish tips or quarries; managed and unmanaged meadows; arable fields; forest margins including shrubby edges. Some sites were assigned to more than one habitat type.Habitat, grouped as follows: urbanity’ .Intensity of human impact: each site was classified according to its location with respect to the limits of the nearest human settlement; this characteristic is termed ‘H. mantegazzianum at a given historical site was used as a measure of the residence time at the site (year).The earliest year of record of mean January and June temperature, sum of annual precipitation) were obtained from a climate atlas (rcGIS 9.2 (http://www.esri.com).Climatic characteristics  and distance from the place of the first introduction into the Czech Republic .The connectivity with potential source populations at the regional scale was characterized by using the following parameters: distance from the nearest neighbouring site (http://www.cenia.cz) was used to determine whether the site was located within a nature protection area (protected areas).A map of landscape protected areas and national parks , riparian habitats (21.5%), roadsides (20.9%) and meadows (20.5%), with other habitats markedly less represented  and ranged from 11.5% to 54.2%, with H. mantegazzianum in meadows and forest margins persisting significantly (P < 0.05) more than expected based on the pooled data, and in roads and parks significantly less; the persistence in other habitats types did not differ from the expected value , with a higher proportion of persisting populations outside (34.2%) than inside (12.8%) urban areas. Of the total number, 188 sites were located inside protected areas , with persistence significantly  higher outside (30.0%) than inside (12.8%) protected areas.Historically, resented . Of the ed value . PersistH. mantegazzianum recorded during our sampling were distributed among habitats in a pattern similar to that of historical localities  among the main groups of habitat types, with the highest persistence in the transport network and riparian habitats, and inter-specific differences reflecting the colonization potential and competitive abilities of the species studied. Heracleum mantegazzianum shows a similar pattern of persistence to R. laciniata, with some differences that can be attributed to eradication efforts targeted at H. mantegazzianum. The most striking differences in the persistence of this species, namely between sites located inside and outside urban areas, can be attributed to increasing public awareness, resulting in the removal of the species from human settlements and their neighbourhood. For example, the low persistence found in road verges, parks and similar habitats reflects increased eradication efforts at sites located close to human settlements, where the species is highly visible and attracts the attention of stakeholders. In contrast, the high persistence in meadows and forest margins indicates the importance of less disturbed habitats with lower human pressure under which the species maintains populations over a long time.Data on native species suggest that habitat destruction or change in land use are the most significant drivers of plant species loss and their diminishing ability to persist in a region  and subsequent spread eastwards (mid-20th century) . This reH. mantegazzianum persisted with a higher probability if the metapopulation connectivity was low; that is, the more populations that were located within the 10-km perimeter, the lower the persistence. A possible explanation is that densely invaded areas may attract more investment in eradication, resulting in the successful removal of some populations. This conclusion seems to be partly supported by how the distance to the nearest neighbouring population affects the persistence of individual populations: among populations located outside settlements and far from the origin of invasion in the country, those located between 0.5 and 1.6 km from the next population showed the highest persistence rate. When above the upper threshold of this range, populations may be too far from each other to profit from the metapopulation connectivity, while those that are within the distance set by the lower threshold may suffer from the abovementioned tendency to attract eradication measures.However, the classification tree revealed one result that is somewhat counterintuitive in terms of the direction of the effect. In meadow sites, populations of The knowledge of species distributions depends primarily on the scale of mapping, the quality of data, and the species itself . As precH. mantegazzianum, the actual figure is approximately doubled (overestimated by 98%). Inferring the distribution of the species from cumulative historical data reported in the literature and herbaria suggests that 237 grid cells are occupied, while the estimate based on the knowledge of species persistence in invaded sites and systematic recent sampling gives 120 grid cells, a figure that is much closer to reality. The degree of bias associated with the distribution of invasive species is likely to be species-specific. However, the level of bias generally depends on the ability of the species to persist in invaded sites, with the inferred distribution becoming less and less realistic as the species’ persistence in the mapped region decreases. The deviation from reality of the inferred distribution based on historical data, which does not account for persistence, will therefore depend on modern floristic knowledge of the region as well as on the species persistence, which is related to the species traits and life history. In some dominant invasive species with clonal growth and high persistence in historical sites  buffers the deviation if the species moves within the same grid. The bias at the level of grid cells can also be assumed to be lower if the species is widespread and abundant over most of the study region. The issue becomes even more relevant when working at a finer scale or with species that have a clustered distribution in the region of interest. If such overestimated distributions are used as a basis for studies of invasion dynamics, there may be an underestimation of real dispersal distances (There are other factors that affect the accuracy of the picture obtained by using past floristic records. First, the magnitude of the bias depends on scale – mapping individual sites will increase the bias, while using grid cells (132 kmHeracleum mantegazzianum is an example of an invasive species for which management measures act as confounding factors, limiting our capacity to predict its distribution based on ecological factors. It needs to be emphasized that the decisive role of management in shaping patterns of persistence in H. mantegazzianum limits the conclusions of our study to noxious invasive species that are often targeted for control or local eradication attempts (see Heracleum mantegazzianum is also somewhat exceptional because it is easy to detect and because of its impact on human health (H. mantegazzianum may make our results less generally applicable to the majority of invasive plant species, they nonetheless show that overestimating the existing infested area is likely to impact negatively on choosing the optimal eradication strategy (strategy , the cor


Silicon nanoparticles of three types  were incorporated into silica aerogels at the gel preparation stage. Samples with a wide range of concentrations were prepared, resulting in aerogels that were translucent (but weakly coloured) through to completely opaque for visible light over sample thicknesses of several millimetres. The photoluminescence of these composite materials and of silica aerogel without silicon inclusions was studied in vacuum and in the presence of molecular oxygen in order to determine whether there is any evidence for non-radiative energy transfer from the silicon triplet exciton state to molecular oxygen adsorbed at the silicon surface. No sensitivity to oxygen was observed from the nanoparticles which had partially H-terminated surfaces before incorporation, and so we conclude that the silicon surface has become substantially oxidised. Finally, the FTIR and Raman scattering spectra of the composites were studied in order to establish the presence of crystalline silicon; by taking the ratio of intensities of the silicon and aerogel Raman bands, we were able to obtain a quantitative measure of the silicon nanoparticle concentration independent of the degree of optical attenuation. Silica aerogels are rigid, highly meso-porous structures with pores on the scale of about 10 to 50 nm with a range of extreme properties: these include low refractive index , low density (greater than 90% air by volume), high optical transparency and low thermal conductivity. They have recently been demonstrated to provide a gas-permeable support for many types of nanoscale materials  grains may be formed by very diverse means: these include the electrochemical etching of bulk single-crystal substrates  followedHowever, only a few studies have been carried out on aerogel-silicon nanoparticle composites, and the main focus has been on Si nanoparticles (rather than porosified Si grains) aimed at optoelectronic applications  though sMetallurgical grade silicon grains of typical size around 4 microns were made porous via stain etching  to produNanoscale spherical silicon particles (Si NS) were produced in a microwave-supported plasma reactor  followed2. PSi NPs or Si NSs in colloidal suspension were introduced into the mixture before the gel formation stage in concentrations from zero to 0.34 mg/ml. The potential problem of particle aggregation has also been considered for the case of Au particles [Silica aerogels were prepared by a conventional one-step base-catalyst sol–gel process (described in more detail elsewhere ) so as tarticles ; we obse2) in order to look for the quenching of the PL by the energy transfer to adsorbed O2.Photoluminescence (PL) measurements were carried out at room temperature in vacuum, with continuous wave 325-nm excitation; low excitation densities in macro-sampling were used, and the PL was detected using a low-resolution single-grating spectrometer and CCD detector. It was also possible to cool the samples to liquid nitrogen temperatures (approximately 80 K) and to admit oxygen gas . This implies that the Raman scattering is now dominated by the remaining solid silicon core of the PSi particles and, therefore, that there is very little of the porous shell remaining . On the basis of these two facts and following earlier work, e.g. [−1) and a second peak due to the nanoparticles; the fit then gives a position of 510 cm−1 for the second band (and FWHM 23 cm−1), which then implies a slightly smaller mean diameter of 2.3 nm for the nanoparticles in the remaining shell. A representative fit and its components (including the aerogel peak) are shown for one LO aerogel in Figure −1, FWHM 23 cm−1) according to the same model [On the other hand, the aerogels containing LO particles show a Raman band that is clearly asymmetric and is shifted to lower frequency  to the aerogel D2 band, we should obtain a quantity proportional to the nanoparticle concentration. The validity of this normalisation depends on the structure of the silica aerogel itself not being modified by the presence of the embedded material. This may not be true; it is known, for example, that the ratio of the D1 to D2 bands gives an indication of water content in silica aerogels [We now consider the concentration-dependence of the Raman scattering bands. Clearly, as the nanoparticle concentration increases and the resulting composites change from highly transmitting to opaque at the excitation energy, the penetration depth of the excitation light and the total scattering volume reduce dramatically. However, the well-defined aerogel Raman Daerogels  and is m2 band is plotted as a function of the mass density of Si NPs introduced into the gel preparation, for each type of nanoparticle. Linear fits to each set of data are shown; these were not constrained to pass through the origin and do not do so exactly. It can be seen, however, that the fits converge near the origin and that the assumption of a linear relationship is reasonable. It is also apparent that the gradient of the linear fits depends on the type of nanoparticle, and this can easily be understood. Firstly, we assume that, in the case of the SO nanoparticles, a significant proportion of the particles is likely to be lost during the gel preparation process, because their mean diameter is much less than the aerogel pore size , and so they are less easily immobilised in the gel network. This accounts both for the weak degree of colouration of these composites and the low rate of increase of the Raman band with concentration. Secondly, the reduction in Raman strength of about a factor of 2 between the LO particles and the LH particles  is qualitatively consistent with our earlier conclusion that the porous shell of the LH particles becomes oxidised, leading to a loss of scattering cross-section of the silicon phonon mode. Of course, the fundamental Raman scattering cross-section for these different types of particle is not necessarily identical, and any variation of this will also lead to a difference in slope of the fits in Figure Figure −1 (Si-O-Si) and 2,000 to 2,200 cm−1  [−1 marked by the dotted line [3 groups indicated by the two arrows [3 coverage leads to a hydrophobic surface). Finally, as one would expect, we see no sign of Si-H modes in the aerogels containing large, oxidised particles, and their FTIR spectra  ,27. On Fted line ). The Sio arrows . The facWe have demonstrated that silicon-silica aerogel composites can be produced by conventional aerogel synthesis with the addition of either nanoscale silicon particles or macroscopic porous silicon grains. Substantial oxidation of the silicon takes place if its surface is partially hydride terminated, and this can be severe enough to remove a large fraction of the porous silicon structure, though a solid crystalline silicon core remains. For oxide-terminated porous silicon grains, however, more of the porous silicon structure survives, though it is (as expected) not active in energy transfer to adsorbed oxygen.The authors declare that they have no competing interests.JA carried out the luminescence and Raman measurements. DW proposed the Raman measurements, contributed to the analysis of the Raman data and carried out the FTIR measurements. BG and SP prepared the Si nanoparticles. DK conceived of the search for energy transfer to oxygen. MG and MR prepared the aerogels, and TAB proposed the use of aerogels for photonic and sensing applications of this type. All authors contributed to planning this work and read and approved the final manuscript.JA, BG, SP, MR and MDWG were postgraduate research students at the University of Bath during this work; DW is a senior lecturer in Physics at the University of Bath with a special interest in optical spectroscopy, and TAB and DK are professors of Physics at the University of Bath with interests in photonics and porous silicon, respectively.


Using molecular dynamics simulations, we have been able to study the CD mediated extraction of cholesterol from model membranes, in particular from a pure cholesterol monolayer, at atomic resolution. Our results show that efficient cholesterol extraction depends on the structural distribution of the CDs on the surface of the monolayer. With a suitably oriented dimer, cholesterol is extracted spontaneously on a nanosecond time scale. Additional free energy calculations reveal that the CDs have a strong affinity to bind to the membrane surface, and, by doing so, destabilize the local packing of cholesterol molecules making their extraction favorable. Our results have implications for the interpretation of experimental measurements, and may help in the rational design of efficient CD based nano-carriers.The depletion of cholesterol from membranes, mediated by  The ability of certain molecules to capture other molecules forming so-called inclusion complexes has a range of potential important applications in e.g. drug delivery and chemical sensing. Here we study the complexation of cholesterol by small oligosaccharide rings named cyclodextrins (CDs). Cholesterol is an essential lipid in the plasma cell membrane, and the ability of CDs to extract cholesterol is widely used in the biomedical field to control the level of cholesterol in the membrane. The molecular mechanism of this process, however, is still not resolved. Using a detailed computational model of cholesterol and CD, we have succeeded to simulate this extraction process. We observe that the CDs are rapidly binding to the membrane surface in a dimeric form, and, provided that the CD dimers are in a suitable orientation, cholesterol molecules are being extracted spontaneously. The cholesterol/CD inclusion complex remains adsorbed on the surface; our simulations predict that the rate limiting step for the actual transport of cholesterol is the desorption of the complex from the membrane. With a clearer understanding of the basic molecular mechanism of the CD mediated process of cholesterol extraction, we can begin to rationalize the design of more efficient CDs in numerous applications. Among all cyclodextrins (CDs), the most abundant are Another important application is the use of cyclodextrins to manipulate lipid composition in different cells. Numerous studies have shown that exposing cells or model membranes to CDs results in removal of cellular cholesterol Despite the substantial amount of experimental effort, the molecular mechanism by which cholesterol is removed remains unclear. The Molecular Dynamics (MD) technique provides a suitable tool to investigate this process at atomistic resolution. Previously, CDs have been simulated in aqueous environment, providing structural, dynamic and energetic information of CD aggregates and various inclusion complexes In this section, we first discuss results obtained from systems in which CD dimers were placed in direct contact with the monolayer surface, in an upright conformation. Under these conditions the uptake of cholesterol occurs readily. We proceed with results obtained with other systems with less biased initial configurations, showing that efficient extraction of cholesterol indeed requires a CD dimer as well as a suitable orientation of the dimer with respect to the monolayer surface. Then we present results from our free energy calculations to quantify the energetics of the extraction process. In the final part, a molecular model for CD mediated cholesterol extraction is presented based on the combined data from our simulations and the existing experimental knowledge.A series of snapshots from a typical cholesterol extraction simulation is depicted in onolayer . In the nterface , in abounterface . Within nterface . Althougonolayer . The tilWe observed that the successful extraction of cholesterol was linked directly to the stability of the ions see  and S2. onolayer , the intThe ability to uptake cholesterol from the monolayer also depends on the orientation of the dimer with respect to the surface. To explore this more systematically, we performed additional simulations in which single dimers or pairs of dimers were placed on the cholesterol monolayer. When a single dimer is placed in direct contact with the surface of the monolayer, it is unable to keep a straight conformation, tilting immediately by ion time . On the D dimers . To remoD dimers . We obse barrels , mostly Our results show that cholesterol extraction is energetically favorable, especially by a CD dimer, but also that tilting and clustering of CDs plays an important role. To understand in more detail the energetics of the whole process, we have considered several sub-processes and calculated the associated free energy changes through calculations of potential of mean force (PMFs) along reaction paths see the  section.The binding of cholesterol to the cholesterol monolayer was also considered . The eneface cf.  and 2. Tormation . As expeormation  and 2 biSee also . The higBased on the results of our simulations, combined with the current body of experimental results, we propose a molecular model for the process of cholesterol extraction by solution , they hasolution  or highesolution . Tilted solution  due to tsolution . Since tarticles  by a sim  for a number of important sub-steps related to the total desorption process, namely i) the extraction of one single cholesterol molecule from the monolayer, ii) extraction of cholesterol from a single  method   can be cFigure S1Stability of (EPS)Click here for additional data file.Figure S2Ineffective cholesterol extraction. Four (EPS)Click here for additional data file.Figure S3Potentials of mean force of key steps of cholesterol extraction. (A) Extraction of cholesterol from CD monomer, (B) extraction of cholesterol from CD dimer, (C) desorption of CD dimer from cholesterol monolayer, and (D) desorption of cholesterol from monolayer. The potentials are shown as a function of the reaction coordinate being the distance between the centers of mass of the extracted molecule and the host system.(EPS)Click here for additional data file.Table S1Association constants of cholesterol with CDs. Association constants K(EPS)Click here for additional data file.Text S1Details about the free energy calculations, and results for control simulations.(PDF)Click here for additional data file.Video S1Simulation of cholesterol extraction from a cholesterol monolayer by cyclodextrins. Initially, CD dimers are in the aqueous phase above the cholesterol monolayer. As the simulation proceeds, the CDs bind to the membrane surface and form aggregates of different kinds. Suitably oriented CD dimers are able to extract cholesterol from the monolayer. The CD dimers are shown in white, cholesterol in grey with red hydroxyl groups. The extracted cholesterol molecules are highlighted in purple. Water is shown transparently.(MPG)Click here for additional data file.


Wheezing is often treated as a crucial indicator in the diagnosis of obstructive pulmonary diseases. A rapid wheezing detection system may help physicians to monitor patients over the long-term. In this study, a portable wheezing detection system based on a field-programmable gate array (FPGA) is proposed. This system accelerates wheezing detection, and can be used as either a single-process system, or as an integrated part of another biomedical signal detection system. The system segments sound signals into 2-second units. A short-time Fourier transform was used to determine the relationship between the time and frequency components of wheezing sound data. A spectrogram was processed using 2D bilateral filtering, edge detection, multithreshold image segmentation, morphological image processing, and image labeling, to extract wheezing features according to computerized respiratory sound analysis (CORSA) standards. These features were then used to train the support vector machine (SVM) and build the classification models. The trained model was used to analyze sound data to detect wheezing. The system runs on a Xilinx Virtex-6 FPGA ML605 platform. The experimental results revealed that the system offered excellent wheezing recognition performance (0.912). The detection process can be used with a clock frequency of 51.97 MHz, and is able to perform rapid wheezing classification. Asthma and chronic obstructive pulmonary disease (COPD) are common around the World. Because of air pollution and other environmental factors, the prevalence of asthma and COPD continues to grow. In 2009, approximately 25 million people in US had asthma, and there were approximately 300 million asthma sufferers worldwide in 2007 ,2. AnalyCurrent methods of diagnosing asthma include auscultation , spiromeIn contrast to traditional manual wheezing detection methods, the use of recording devices to collect and analyze lung sounds has been extensively studied in recent years. The identification of abnormal lung sound characteristics using signal processing methods could help physicians to identify physiological mechanisms generated by lung sounds and their associated pathological links . BecauseIt has been medically proven that asthma is a chronic disease from which recovery is not possible. Asthma sufferers have a high risk of suffocation when their asthma is acute, and 250,000 annual deaths are attributed to the disease [Wheezes are abnormal respiratory sounds that occur for certain duration of time. According to computerized respiratory sound analysis (CORSA) standards , wheezinImproving recognition accuracy thus often requires an immense number of computational resources, and is difficult to implement on portable devices. Therefore, most conventional automatic wheezing detection systems have been built using desktop computers. To implement an automatic wheezing detection system on a portable device, digital signal processors (DSPs) are commonly used . AlthougThus, the field-programmable gate array (FPGA) is ideally suited for building a portable rapid wheezing detection system. Such a portable system can be accelerated by applying an image processing algorithm using parallel computing hardware. The characteristics of wheezes in spectrogram can be treated as quasihorizontal lines with strong amplitude. Thus, there are many image processing techniques combined to preserve these characteristics and filter out unwanted noises. In order to achieve quick response to wheezing events, the frame blocking technique, which divides a spectrogram into sections of two seconds, can reduce responding time and demands of computing resources. Simultaneously, an optimal parameter set for support vector machine (SVM) model proposed in this research shows good accuracy and sensitivity of wheezing recognition. The proposed system was built as an independent wheezing detection silicon intellectual property (WDSIP), able to be integrated with other functional silicon intellectual properties (SIPs), e.g., universal asynchronous receiver/transmitter (UART), direct memory access (DMA), on system-on-programmable-chips (SoPCs) using the peripheral local bus (PLB) and MicroBlaze processor provided by Xilinx. This allowed for greater portability and reduced system volume. In contrast to a customized IC, an FPGA can be modified repeatedly, and can be flexibly integrated with other SIPs. Preprocessing: A short-time Fourier transform (STFT) is used to acquire an image containing the time-frequency relationship of the wheezing sound (spectrogram).Forming an Image Mask from the Spectrogram: Noise is filtered using a bilateral filter and image processing methods  are used to pinpoint wheezing. A sifting process using two rules based on CORSA standards is also applied to ensure that objects in the image mask are wheezes.Feature Extraction and Classification: Features which represent the wheezing components on the masked spectrogram are extracted and classified using an SVM.The processing flow of our wheezing recognition system is shown in Image processing of the spectrogram is the most crucial part of this process. Traditional methods directly analyze the edge of the spectrogram to detect wheezes ,20, or cBilateral filtering is used to both smooth the image by removing outliers, and preserve strong image edge components by giving both spatial and photometric domains weighted coefficients.Edge detection and multithreshold segmentation are combined to preserve image edges and retain high and isolated peaks during analysis.The proposed wheezing detection system was built as an independent WDSIP. The system was built in accordance with SoPC design flow, allowing a number of subsystems to be integrated into a single FPGA, and enabling data transmission between subsystems to be conducted completely on-chip. This reduced I/O speed requirements and additional IC usage of the target platform. This design also allows the system to be used independently or as a part of a broader physiological parameter measurement system.The Embedded Development Kit (EDK)  is a sofi.e., the ZigBee module). Therefore, the WDSIP was implemented using a PLB interface [The proposed WDSIP requires a PC or a recording device to transfer data through the UART interface  to control the internal processing flow . MicroBlOur control FSM is based on the concept of the Moore machine, and its processing flow is shown in Wheezing is characterized by its fundamental frequency and harmonics. Because these characteristics are continuous, spectrograms of wheezing present as quasihorizontal lines that reveal the strong presence of a determined frequency over a period of time. We designed a WDSIP able to rapidly distinguish the distinct edges of these wheeze episodes from background sound components on spectrograms. The main IPs of the WDSIP is described as follows.After the WDSIP collects a frame of sound data, the FSM enters the STFT stage. To implement an STFT with a 50% overlapping Hanning window, the data must be temporary stored in dual-port RAM with a depth of 256. The operational mode of the dual-port RAM was set to read-after-write, allowing the just-stored data to be present on the output port with one cycle delay. This data is multiplied with the weights of the Hanning window to obtain the first data frame. The remaining port waits 128 cycles, then reads the next 128 points, to compute the second data frame, and so on. The actual hardware implementation for the 50% overlapping Hanning window is shown in The bilateral filter implemented in our WDSIP is based on that in . We implThe length of the delay line is related to the size of the image. The delay line was not implemented using shift registers, because processing large image sizes requires substantial hardware resources. The delay line in our system was implemented by using RAM, as shown in Bilateral filter can perform edge-preserving smoothing by applying weights which depend on Euclidean distance and radiometric difference of pixels. In order to reduce the demands on computational resources, the 7 × 7 filter mask can be divided into eight groups because the geometrical location of the mask is radially symmetric. Furthermore, the coefficients of the filter are quantized and stored in the look-up tables (LUTs) to avoid using exponential function. In multithreshold image segmentation, a threshold is applied to a filtered spectrogram, an image object on the thresholded image is labeled, and the image objects are isolated using rules. The implementation of the image labeling system in hardware is shown in In order to isolate all wheezing components, the multithreshold image segmentation, which may require several iterations to apply different thresholds to filter images and check the characteristics of the image objects according to their time and frequency information, becomes the most time-consuming process in the proposed WDSIP. To maximize its speed and use of hardware resources, the solution is adding dual-port RAM and applying pipeline technique to image labeling system to achieve the highest possible clock rate and data throughput. However, only one port of the dual-port RAM can output pixels from the filtered image memory at the highest clock rate, because the other port is at the same time being used to implement the bilateral filter to write the output the filtered image; thus, the operational frequency of this port is 1/8 slower than the highest frequency in the system. As shown in Because multithreshold image segmentation only checks the amplitude of the filtered image, many image objects it identifies meet CORSA standards, but not all of them are wheezing components. Edge detection thus extracts quasihorizontal lines with strong gradients from the image. Combining multithreshold image segmentation and edge detection to form an image mask, the spectrogram is masked, and the remaining objects, which are characterized by strong power intensities and strong edges, are considered wheezing components. The hardware implementation of the Prewitt operator for edge detection is shown in CY: Frequency located at the centroid of the wheezing episode.PT: Time duration of the wheezing episode.PS: Slope of the wheezing episode.PAR: Area ratio of the wheezing episode/bounding box of the wheezing episode.PWe applied the SVM classifier to predict whether sound data contained wheezes or normal sounds, based on the image properties of the spectrogram objects identified by the mask. As shown in These parameters were used to represent the shapes of the objects, and reduce the complexity of the classifier. σ which yielded the most satisfactory result. The SVM classifier must be trained for wheezing recognition before implementation. We used the RBF kernel function and grid search method to determine the corresponding T, PS) and . After we trained the SVM, we used the trained models to classify the testing samples. The performance (PER) of the recognition system was estimated by calculating the sensitivity (SE) and specificity (SP), defined in the following equations:The training sample results revealed that the proposed system achieved an accuracy of up to 96.63% using the parameter sets  and , as shown in T, PS), because these parameters used fewer hardware resources. The results of the implementation of this SVM in hardware are shown in The testing samples were analyzed using various parameter sets. The recognition system exhibited superior performance using the parameter sets (P32) to a file, and sent this file to the platform, where a program we had written compared the received data with an accumulator, the estimated error rate of UART transmission was obtained. The results show that no errors were observed when these 4,294,967,296 testing samples were sent to the platform.Identical testing samples were sent to the platform through the UART port to confirm the wheezing detection performance of the WDSIP after the implementation of all functional blocks in hardware. Tera Term was used to connect the platform and set the band rate of serial port to 115,200 bps, to estimate the reliability of the UART transmission from a PC to the platform. We wrote a data set  still required considerable multipliers and adders. Thus, bilateral filtering was found to be responsible for the second-highest hardware resource demands in the system. We applied a 7 × 7 window when processing the spectrogram by using bilateral filtering, but it is necessary to process more pixels than such a window allows at a time. Although we optimized the architecture of the bilateral filter by dividing the input pixels into eight subgroups, the internal stage of the bilateral filter  process, which reduces the logical and signal power, can perform low power consumption further.However, the system still has considerable space for improvement: Its hardware must be optimized to reduce demands on hardware resources, and enhance its commercial applicability. Moreover, noise disturbances, and the computational error rate resulting from fixed-point operation, must be more adequately managed. Peripheral devices for the system, such as LCD displays or storage, must also be designed to enable doctors to use the system to diagnose lung diseases, and to allow the system to be implemented in remote medical assistance applications.


Elucidation of the relationships between malaria incidence and climatic and non-climatic factors in a region is of utmost importance in understanding the causative factors of disease spread and design of control strategies. Very often malaria prevalence data is restricted to short time scales (months to few years). This demands application of rigorous statistical modelling techniques for analysis and prediction. The monthly malaria prevalence data for three to five years from two cities in southern India, situated in two different climatic zones, are studied to capture their dependence on climatic factors.The statistical technique of response surface method (RSM) is applied for the first time to study any epidemiological data. A new step-by-step model reduction technique is proposed to refine the initial model obtained from RSM. This provides a simpler structure and gives better fit. This combined approach is applied to two types of epidemiological data , for two cities in India with varying strengths of disease prevalence and environmental conditions.The study on these data sets reveals that RSM can be used successfully to elucidate the important environmental factors influencing the transmission of the disease by analysing short epidemiological time series. The proposed approach has high predictive ability over relatively long time horizons.This method promises to provide reliable forecast of malaria incidence across varying environmental conditions, which may help in designing useful control programmes for malaria. Malaria is one of the world's major micro-parasitic infections in humans killing nearly two million (mostly children) each year, in addition to more than 500 million people living in the epidemic regions. It has been estimated that almost half the world's population is at a risk of the disease ,2. MalarEpidemiological research on micro-parasitic infections such as malaria, is often based on two separate measures of parasite distribution among hosts  - the incidence of the disease, and the infection prevalence. The incidence or prevalence measures are primarily based on classifying the population under study with respect to a range of factors such as age, sex, social factors, environmental variability etc. The climatic and environmental factors affect production and survival of the vector (mosquito), and the speed of parasitic life cycle -12. SuchGiven the fact that data collection is mostly restricted to short time scales (months to few years), in recent studies, researchers have used elaborate time series analysis models to show seasonality pattern in malaria incidence, and the Monte-Carlo Markov Chain methods with Bayesian techniques of a-priori probability assignment, to estimate the risk factors -24. Howea priori assumptions on independent or response variables (discrete or continuous). Two types of epidemiological data for malaria cases are considered - i) a three-year time series data of Slide Positivity Rates (SPR) values of malaria for Chennai, and ii) a five-year time series of Total Malaria cases (TMC) for Mangalore. The RSM models delivered good predictive ability over long time horizons. In addition, a step-by-step model reduction technique is proposed to refine the initial model obtained from RSM, which not only provides a simpler structure but also gives better fit as supported by Akaike's Information Criterion [In this paper, the incidence of malaria in two cities in southern India - Chennai and Mangalore - in two different climatic zones, are studied using the Response Surface Method (RSM), which was first introduced to obtain optimum conditions in a chemical investigation  and thenriterion . The stuMalaria incidence data, along with different demographic and environmental factors, were collected from literature and different other sources for two cities in India - Chennai and Mangalore ,34-38. BMalaria is endemic in both the cities for the last few decades, though Chennai has lower endemicity compared to Mangalore. They are victims of rapid industrialization, witnessing an unprecedented spurt in construction activities in recent years, thus facing the problem of mosquito breeding in man-made clear water sources like wells, overhead tanks, sumps, cisterns as well as other defective and illegal drainage systems. Yet there are several differences between them, specifically in their demographic and climatic factors. Mangalore has less population  as compared to Chennai  according to the 2001 census of India. In addition, the urban area in Mangalore has 32 recognised slums, and nearly 22,000 migrant labours live in slums within the city limits, whereas, Chennai has the fourth largest population of slum dwellers among major cities in India, with about 820,000 people (18.6% of its population) living in slum conditions .Plasmodium vivax and Plasmodium falciparum), show similar temporal patterns of disease incidence, and therefore are combined together for further analysis.Two types of data for malaria incidence, Slide Positivity Rate (SPR) and Total Malaria Cases (TMC), along with different demographic and environmental factors were collected from Chennai and Mangalore. The data for two types of malaria  values, the dependent variable under study, were obtained from the Corporation of Chennai, Tamil Nadu, India for two types of malaria, in India . A thin in India . The envin India .The SPR values (bars) and the environmental variables, including population (lines), for Chennai are presented in Figure P. vivax and P. falciparum cases) are the measures of malaria incidence, which are different from the numerical nature of SPR values. The total malaria cases include both symptomatic and asymptomatic cases. Also, average monthly values of temperature, humidity, and rainfall for the same interval were computed from a weather database that gives the daily minimum and maximum values for these variables [Monthly malaria cases from January 2003 through December 2007 (60 time points), were obtained from Mangalore city, Karnataka . These Tariables . Mangaloariables . It receThe TMC values and the climate variables are presented respectively as bars and line graphs in Figure It may be noted here that the data for climate variables were obtained from daily weather sources, and they were averaged to monthly scale to ensure compatibility with the monthly parasitological data (SPR and TMC). Being in a tropical climatic region, the climatic variables for both the cities show small daily variations and hence the choice of arithmetic mean for calculating the monthly averages is appropriate and easy to apply. Also, none of the data are measured in logarithmic scale, or are highly skewed, or show high variations, hence geometric mean is not considered here .Before the model development is discussed, statistical techniques for exploring the relationships between dependent variables  and independent variables  are presented. The details are given in Additional File at lag one is expected to be important among other lags since values at the previous time point tend to correlate closely with those of the current time.Autocorrelation of any time series data describes the correlation and relation in general between values of the series at different points in time . Intuitiρk at lag k, for sample size n and testing for cumulative autocorrelation for h lags, LB is given byPresence of autocorrelation was studied for the independent variables (SPR and TMC)  are also considered as independent variables in the model. For SPR and TMC values, autocorrelation values t-statistic was used for testing of significance. The two-sided t-statistic for a correlation, r at α level of significance is given byLinear dependencies were quantified using correlation, and Correlations at different lags  affecting the optimum response in the variable of interest - the dependent (response) variable [Response Surface Method (RSM) is a classical optimization technique that integrates mathematical and statistical approaches to the problem of finding the values of several independent variables  similar to that obtained in the initial model fitting through RSM. Figure S4 in Additional File The foremost task in this process is to enlist the resultant orders of magnitude of each term. In a model, each term consists of two components: the variable - linear or quadratic and the corresponding estimated coefficient or parameter value. The resultant order of a term is defined as the sum of the orders of the variable and the parameter in scientific notation. This exercise asserts its importance in cases when there is a great disparity between the orders of the variable and the parameter of a single term. Even though the parameter has very low order, a high order of the variable component may render the resultant order to become higher than that of the response, which may finally lead to its exclusion from consideration for the next step and vice-versa.2) is examined at each step of the model by removing each term, beginning with the term with the smallest resultant order  at each step, to decide about the retention or removal of the term under consideration. This process is continued till the terms with resultant orders equal to that of the response or higher are reached. Here, the underlying assumption is that the contribution of a term in a particular model equation is proportional to its resultant order. This is similar to backward regression, since the removal of terms from the model is performed once all the independent variables as well as corresponding possible terms up to second order have been included in the model. R2 is employed for the decision of retaining or removing the terms in the model since it is a statistic traditionally used for providing the measure of the proportion of the variation explained by the model [Following the above process, the coefficient of determination  described above to arrive at the decision of retaining or removal of terms in the model will vary according to the nature of response being studied and variation in the allowed amount of loss in accuracy owing to model reduction.To assess the goodness of fit for the initial models using RSM and the reduced models using model reduction technique, four diagnostics tests are carried out: (a) Confidence Intervals for the data points, which are used for fitting the model, (b) Akaike's Information Criterion to determine the better fit model, (c) Prediction Intervals in Forecasting Method for the data points estimated from the reduced model but not used for fitting the model, and (d) Collinearity Analysis for testing homoscedasticity of the residuals.Using Gauss Markov Theorem , it is tn observations, having k parameters and the residual errors denoted as ∈i,i = 1,2,..,n, the value of the criterion is given by formula (3).This statistic measures the appropriateness of forecasts of the estimated statistical models and selects the better model from the given models ,40. The 2 for reducing the number of terms in the model does provide us with a model that attains a trade-off between the variation explained and the number of parameters estimated.AIC has been used to substantiate the claim that considering ROnce the reduced model is obtained, using 80% of the available data, the next step to validate the model is to test the forecasting ability. This is performed by employing the model to predict values for the remaining 20% time points. Since the model incorporates auto-regressive terms , this prediction ensures that each estimated response serves as an input for the subsequent estimate. This means that the predictions use the model prediction as the input for successive estimates, in addition to reliable climate forecasts and/or population projections. Further, this feature leads to training the data on hitherto unforeseen terrain, making it more conducive to unknown data. Using ancillary statistics , the 95%For a least square regression approach, it is imperative for the residuals to be able to adhere to the assumption of constant variance. This property is also known as homoscedasticity. Two different measures are considered, namely, the Variance Inflation Factor and Breusch-Pagan test , for anaSeveral tools and software are used for different statistical analysis and model fitting to the data. MS Excel was used for data handling. The model computation and verification of results was performed using MATLAB  and the The RSM models and their modified forms are discussed below for two types of malaria incidence data - SPR and TMC values - in two cities of India - Chennai and Mangalore. The important independent variables  are assessed using the step-wise model reduction process (described in Methods section), which offer better models as well as reliable predictions for these two cities.t-statistics , average temperature (T), population (P), rainfall (R) and average temperature-at-lag-one (T-1). The non-linear relationship shared between the independent variables (except SPR-at-lag-one), and the SPR values, were confirmed using residual plots  of 91.53%.Figure 2 at each step and making the decision for removing or retaining a term accordingly  compromising only less than 2% decrease in the value of R2. Figure 2.The reduced model (Eqn.5) has R3827.692 and 3410.028. It is clear that the reduced final model is indeed better owing to its lower AIC. For model validation the 20% of the SPR data (June to October 2004), which were not utilized for building the model, were estimated from the final model. Figure The AIC for the initial and final models for Chennai are - -1), average temperature (T), rainfall (R) and average temperature-at-lag-one (T-1). Also, even though the lag-two TMC variable (TMC-2) showed significant autocorrelation, it is not considered as an additional independent variable since the number of cases in the present month is considered to be directly influenced by the previous month only [The TMC data for Mangalore city covers 60 months, from January 2003 through December 2007 Figure . This danth only .The linear correlation between TMC and the climate variables . Further attempts to remove terms , and hardly reduces the RMoreover, to assess the linear accuracy, homoscedasticity and to observe the differences after removing lower order variables, residual plots for the initial and reduced models have been plotted for both SPR and TMC values  and a simple model reduction method is applied to describe the incidence of malaria in two geographically, ecologically and demographically different cities in India  for two types of epidemiological data - Slide Positivity Rates (SPR) values of malaria for Chennai and Total Malaria cases (TMC) for Mangalore. This approach shows the applicability of the algorithm to different measures of incidence of malaria. The analyses of the parasitological data for the two Indian cities using the RSM approach not only capture the essential dynamics of the disease incidence, but also show the influence of different climatic and non-climatic factors. For both Chennai and Mangalore city, it is clear from the final model equations that previous incidence of the disease, Temperature as well as Temperature-lag-one and Rainfall have strong influence on the disease incidence and play important roles to shape the disease curve. The predictions for Chennai city do not show any clear trend for the disease to decrease but show more monthly periodic variations. But for Mangalore city, the prediction show initial decay in the total malaria cases from February to May, then show an upward trend till August, and finally decreasing again till December following the pattern of rainfall distribution of that region.RSM is a global approximation method which is ideally suited for solving problems with a relatively noisy response, where a gradient based method would lead to a local optimum instead of a global one . The Sec2).A model reduction method is introduced, which ensures filtering of terms that do not make valuable contribution to the fit of the model. It is a simple but useful approach, and has no underlying assumption except that the contribution of a term in the model is directly proportional to its order of magnitude. Based on this, a criterion to remove terms from the model without a significant change in the coefficient of determination is successfully outlined. At each step of the model reduction, it is ensured that the predictions remain within the confidence limits that minimize error variance. It is worth noting here that the proposed model reduction technique simplifies the model structure by reducing number of coefficients (terms) by almost 30% compared to the initial model by RSM without reducing the coefficient of determinant values significantly  compared to previously reported values (63.85%) observed on the same data using a different regression method [The results based on the initial model by RSM, and final model through the proposed model reduction technique, show good fits for both the data types in two different cities Figures  and 4. In method . Using AThe comparison of initial and final model formulations (Eqns. 4 and 5) for the SPR values in Chennai city reveals some interesting features. The final model not only contains less number of dependent terms but also shows reduction of direct dependence of both linear and higher order terms for rainfall. The dependence of SPR on rainfall in this final model (Eqn. 5) is only depicted by the interaction terms associated with other factors, such as temperature and population size. This feature is also observed in the original data Figure  as the vSince the observed and estimated values do compare well, we would like to infer that these techniques of modelling (the RSM and the model refinement/reduction method) perform well for analyzing epidemiological data and may be useful for forecasting purpose, provided reliable climate variable estimates and population projections are available.Mathematical analysis of the models may not always capture the essential features of the disease transmission process, as it is sometimes difficult to understand the direct and interacting effects of temperature, seasonal forcing, excessive rainfall, correlation between different variables and other model parameters. Also, among the innumerable statistical models based on malaria incidence data, only a few approaches have shown promising results. The results of these models are mostly data specific, and applicable primarily to the particular data set studied. Therefore, there is always a need for suitable models and methods to understand the important features of the epidemiological data for providing better predictions.In this paper the Response Surface Method (RSM) is applied for the first time in analyzing epidemiological data, specifically for malaria. It has been shown here that this method models the existing time series data well. The model is subjected to further analysis and development of a simpler, but statistically good, reduced model, which can offer better forecast of the disease. Since the major challenge is to ascertain the detailed understanding of the different environmental factors, previous incidence of the disease and their influence on the prevalence pattern, a reduced model with fewer terms is helpful for clearer understanding and reliable predictions.The interesting effects of climatic and non-climatic factors, such as previous disease incidence, population, are clearly visible from the analysis. The model predictions capture the climatic variations, mainly rainfall and temperature, for both the regions under study and resembles well with the observed disease incidence. This approach leads to detection of the most crucial environmental factors influencing the transmission of the disease while offering a coherent and integrated understanding of the disease process in any area. Thus, the proposed combined method gives a simple, but highly predictive model for malaria incidence without compromising on the proportion of variation represented and may be useful for public health professionals for adopting better strategy not only to control malaria but for other infectious diseases, if suitable climatic information and disease prevalence data are available.The authors declare that they have no competing interests.SBR carried out the theoretical analysis, and contributed in writing the manuscript. RRS contributed in theoretical analysis and formulating the approach, and writing of the manuscript. SS conceived the idea for the article, and contributed to designing the study and writing of the manuscript. All authors read and approved the final manuscript.Statistical techniques and Model Reduction Process. The additional information provided describe the statistical techniques used for exploring the relationships between dependent variables  and independent variables  and the details of the model reduction process . [ S1-S5). -42.Click here for file