Analysis and estimative of schistosomiasis prevalence for the state of Minas Gerais, Brazil, using multiple regression with social and environmental spatial data

The aim of this work is to establish a relationship between schistosomiasis prevalence and social-environmental variables, in the state of Minas Gerais, Brazil, through multiple linear regression. The final regression model was established, after a variables selection phase, with a set of spatial variables which contains the summer minimum temperature, human development index, and vegetation type variables. Based on this model, a schistosomiasis risk map was built for Minas Gerais.     

Species richness along a production gradient: a multivariate approach

The specific shape of the relationship between plant diversity and productivity and the causal mechanism(s) behind the observed pattern(s) are still highly debated. Recent advances suggest that the relationship depends on several environmental variables and may change with the observational scale. In this study, a multivariate, multiscale approach was used to identify the variables that determine the relationship between species richness and annual production along a forest/old field edge in southern Québec (Canada). Various relationships between richness and production were found at different distances to the edge. In the forest, most relationships were positive and linear, while in the old field the relationship shifted from positive linear to non-significant with increasing distance from the edge. In the forest or in the old field, the shape of the relationship (all distances from the edge combined) was unimodal. Path analyses showed that species richness was determined mostly by production, which was influenced by different limiting resources, depending on the community (forest or old field). An increasing range in production created by pooling across community types can confound the resources and/or conditions determining the diversity-productivity relationship.     

Interaction between Natural Selection for Heterozygotes and Directional Selection

Significant correlations between allelic frequencies and environmental variables in a number of insect species have been demonstrated by multivariate techniques. Since many environmental variables show a strong relationship to geographic location and since gene flow between populations can also produce patterns of gene frequencies which are related to the geographic location, both selection and gene-flow hypotheses are consistent with the observed correlations. The genetic variables can be corrected for geographic location and so for linear gene-flow patterns. If, after correction, the genetic variables still show significant correlations with similarly corrected environmental variables, then these correlations are consistent with hypotheses of selection but not of gene flow. The data of Johnson and Schaffer (1973) have been reanalyzed using the method of canonical correlation after correction for geographical location by means of multiple regression. Five of the nine loci studied exhibit significant canonical correlations. These results, under the assumption of linear gene flow, support hypotheses of selective action of environmental variables in the genotype-environment relationships observed.     

Mathematical coupling of data: correction of a common error for linear calculations

The need frequently arises in the scientific environment to investigate the relationship between quantities that are calculated from a common set of directly measured variables. However, the presence of error in the common set of measured variables distorts the relationship among the calculated quantities and can lead to incorrect conclusions. This article presents a method of correcting for such distortions in the Pearson correlation coefficient and in the linear regression coefficient for linear calculations involving two measured variables. The errors considered may be either independent of, or proportional to, the value of the variable being measured. Tests to determine whether these popular coefficients have values significantly different from zero are presented. An example from the physiology literature is presented to illustrate these techniques.     

Predicting badger sett numbers: evaluating methods in East Sussex

Abstract. One way in which a species' numbers may be estimated without direct counting is to predict their dispersion and density from more readily available habitat measures, such as landscape variables measured from maps or vegetation variables measured in the field. We compare the power of ordination and regression techniques for predicting badger ( Meles meles L.) numbers at a local scale, using a land class system, map-read landscape variables and field-derived vegetation variables. Sett density was used as a surrogate of badger density. Multiple linear regression using vegetation and landscape variables together gave the most accurate prediction of sett density, while ordination techniques were of lesser value. The addition of vegetation variables to landscape variables did not substantially improve the power of ordination. Outlier Sett Density was predicted more accurately, and by different variables, to Main Sett Density. The relationship between badger ecology and habitat variables that were useful in predicting sett density is discussed.     

降水量和温度对植被覆盖指数影响的空间非平稳性特征——以新疆伊犁河谷地区为例

多变量空间相关分析多基于时间序列数据,对数据时长与统计要求严格,空间非平稳性特征分析可以利用单期数据分析多变量之间的相关性。通过空间变系数回归模型分析了2006年和2011年的新疆伊犁地区降水量和温度对植被覆盖度指数影响的空间变化特征,利用局部线性地理加权回归(GWR)方法估计得到了回归系数曲面,揭示出变量间相互影响的空间异质性,同时利用线性回归最小二乘估计进行了对比。结果表明:(1)空间变系数回归模型可以用于变量间的空间相关分析;(2)局部线性GWR估计方法明显优于线性回归最小二乘估计;(3)拟合结果表明,伊犁地区降水量和温度对植被覆盖指数的影响具有显著的空间非平稳性特征;(4)模型估计误差是降水、气温之外的地形、地貌及人类活动等多种因素造成的,需进一步研究。方法可为具有空间非平稳性特征变量间空间相关性分析以及植被覆盖指数的空间模拟分布提供思路和方法。     

Phytoplankton richness is related to nutrient availability,not to pool size,in a subarctic rock pool system

In small aquatic ecosystems, communities are strongly affected by environmental filtering such as disturbances and fine-scale heterogeneity of physicochemical properties. Aim of this study was to examine the effects of abiotic variables on phytoplankton richness in 30 subarctic rock pools in Finnish Lapland and further to test species–area and productivity–diversity relationships. We used Moran’s correlograms to examine if phytoplankton richness and explanatory variables show spatial autocorrelation. We then related phytoplankton richness to physical, chemical and spatial variables (derived from Principal Coordinates of Neighbor Matrices based on either overland or water course distances) using generalized linear model (GLM). Correlograms did not indicate clear gradient-like spatial structures in the data. According to the best-approximating GLM, phytoplankton richness showed a highly significant positive relationship with total P concentrations, which differed by one magnitude among the pools, and showed also a marginally significant negative relationship with conductivity. Richness scaled nonsignificantly with pool volume. We conclude that rock pools with higher nutrient availability are capable of supporting more phytoplankton species in this low-energy ecosystem. We did not find any support for the species–area relationship across the pools possibly because the pools were similarly affected by random disturbances irrespective of their volume.     

Factors affecting resolution, band width, number of theoretical plates, and apparent diffusion coefficients in polyacrylamide gel electrophoresis

A systematic study of several variables affecting band width and resolution in polyacrylamide gel electrophoresis (PAGE) has been carried out. This makes it possible to determine resolution, number of theoretical plates, and an apparent diffusion coefficient in PAGE. Measurement of band position yields a linear relationship between logarithm of electrophoretic mobility and gel concentration when other variables are held constant. Similarly, measurement of band width yields a linear relationship between the logarithm of the dispersion coefficient (D′) and gel concentration. This makes it possible to extrapolate to 0 gel concentration and to obtain as estimate of a free dispersion coefficient (D′₀) which is usually one or two orders of magnitude greater than the free diffusion coefficient (D_20,w). D′ depends on protein concentration (which is a function of sample load and time), on ionic strength (I), and on duration of electrophoresis (dependent on field strength which in turn depends on ionic strength and current). Since these several variables introduce nonlinear and interrelated correction factors, extrapolation to “infinite ionic strength,” “zero concentration,” and “infinite time” becomes difficult although it is potentially feasible at both the experimental and the theoretical level, and thus it may be possible to determine diffusion coefficients in PAGE on microgram amounts of material without the need for preliminary purification. Alternatively, PAGE in a nonsieving, anticonvectant gel at high ionic strength and for long duration may be able to provide an estimate of D_20,w. The results also support the validity of previously developed approximations for the relationship between band width and gel concentration, and for the relationship between band dispersion and electrophoretic mobility.     

Studies on the toxicity and binding kinetics of abrin in normal and Epstein-Barr virus-transformed lymphocyte culture-I. Experimental results - 4

The effects of treatment with varying doses of abrin, a D-galactose binding lectin, on DNA and protein synthesis of normal and Epstein-Barr virus (EBV)-transformed lymphocytes have been previously investigated. Using data on EBV-transformed lymphocyte cell density as a function of both time and dose of abrin, the authors introduced the concept of self- and cross-coupling metabolic variables as a means of understanding how abrin affected DNA and protein uptake. In this paper, the self-coupling constant is studied in more detail and the relationship between DNA and protein synthesis is further expanded. We find that there is a significant linear relationship between DNA and protein synthesis in normal lymphocyte culture as measured by abrin interaction in the culture. We further find that there is a much stronger relationship between these variables in EBV-transformed lymphocyte culture. This relationship is further examined, and possible analytic equations are expressed.     

A Statistical Modelling Approach to the Occurrence and Timing of Reconciliation in Wild Japanese Macaques

In various social species, animals have been observed to share friendly relationships with some group members and to resolve conflicts through reconciliation, the exchange of affiliative behaviour soon after a conflict that functions to restore the relationship between the former opponents. The valuable relationship hypothesis predicts that reconciliation should be observed more often after conflicts between friends. Friendly relationships can be described by three dimensions (i.e. value, security and compatibility); however, research into the relative importance of these dimensions for the occurrence of reconciliation is sparse. Moreover, reconciliation may depend on factors other than the social relationship between opponents including, for example, their social status or the context of the conflict. Our study aimed at analysing which factors are important determinants of reconciliation and at testing the valuable relationship hypothesis, by analysing the relative effects of relationship value, security and compatibility on the occurrence and timing of reconciliation. We collected data on two troops of wild Japanese macaques living on Yakushima Island, Japan, and selected the best predicting variables of reconciliation using linear mixed models. Our results show that reconciliation occurs more frequently, and earlier, after conflicts between opponents who exchange a higher percentage of grooming. Two additional variables related to relationship security and value were selected in the best models: frequency of aggression and of approaches resulting in tolerated co‐feeding. Among the variables not related to relationship quality, distance between opponents at the end of the conflict, kinship, sex of the opponents and context of conflict (i.e. during feeding or social time) were included in our models. Our findings support the valuable relationship hypothesis and, in particular, highlight that the fitness‐related benefits of social relationships (i.e. the relationship value) are important determinants of the evolution of friendly relationships and reconciliation.     

Is it possible to predict the salinity of Iberian salt lakes from their conductivity?

Conductivity measures have been widely used to estimate salinity, an obvious feature of salt lakes. Regression analysis using log-log linear model provides an adequate approach to the study of the relationship between both variables. However, actual use of that kind of statistical model suffers too frequently from lack of correctness. We have studied conductivity-salinity relationships for 69 salt lakes (128 samples) on the Iberian peninsula. Despite the satisfactory fit of the data to the model (r² = 0.88), predictive efficiency is shown to be low. This feature, which is likely to be common to this relationship anywhere, is mainly related to heterogeneity in ionic composition.     

The roche vault performed by elite gymnasts: somersaulting technique, deterministic model, and judges' scores

The purpose of the study was to determine the mechanical variables that are related to successful post-flight somersaulting performance of the Roche vault. The 23 Roche vaults performed during the 2000 Olympic Games were filmed by a 16-mm camera operating at 100 Hz. The 2-D direct linear transformation technique was used for spatial calibration. Approximately 60 frames were digitized per vault. The method of Hay and Reid (1988) was used to develop a deterministic model to identify the mechanical variables that govern linear and angular motions of the vault. Correlational analysis was used to establish the strength of the relationship between the mechanical variables identified and the judges' scores. Significant correlations indicated that the higher judges' scores were negatively related to five mechanical variables and positively related to seventeen variables in the model. The normalized horizontal displacement of body center of mass (CM) from the knee grasp to the peak of post-flight was the best single predictor of the judges' score and accounted for 50% of variation in the judges' score. Finally, the landing point deductions and the official horizontal distance of post-flight collectively accounted for 86% of the variance in the judges' scores.     

Estimating linear causality in the presence of latent variables

Learning causality from data is known as the causal discovery problem, and it is an important and relatively new field. In many applications, there often exist latent variables, if such latent variables are completely ignored, which can lead to the estimation results seriously biased. In this paper, a method of combining exploratory factor analysis and path analysis (EFA-PA) is proposed to infer the causality in the presence of latent variables. Our method expands latent variables as well as their linear causal relationships with observed variables, which enhances the accuracy of causal models. Such model can be thought of as the simplest possible causal models for continuous data. The EFA-PA is very similar to that of structural equation model, but the theoretical model established by the structural equation model needs to be modified in the process of data fitting until the ideal model is established.The model gained by EFA-PA not only avoids subjectivity but also reduces estimation complexity. It is found that the EFA-PA estimation model is superior to the other models. EFA-PA can provides a basis for the correct estimation of the causal relationship between the observed variables in the presence of latent variables. The experiment shows that EFA-PA is better than the structural equation model.     

An analysis of density responses of forest and woodland birds to composite physiognomic variables

Habitat ordinations were performed on 37 sites in forests and woodlands along a latitudinal transect that spanned over 250 km in central Victoria. Australia. Multivariate analyses of these data by using nonmetric. multidimensional scaling (AIDS) were used to generate composite variables. The relationships of these composite variables and densities (by area) of 58 species of forest and woodland birds were assessed by using linear and polynomial regressions. Only seven of the 58 species of birds did not display a significant relationship to one or other of the five composite variables. Approximately 50% of the avian species showed significant relationships with each of the first two composite variables, but lower percentages were observed for the other three variables. About a third of all significant correlations were either of second or third order, ft appears that marked curvilinearities associated with the first composite variable can be interpreted as linear responses with respect to the secondary composite variable. These results suggest that, although composite variables derived from multivariate classifications are statistically independent, there often may be substantial biological dependence between the composite variables. Therefore, for biological interpretation, it would be appropriate to regard composite variables derived from multivariate classifications as suites of related variables. Some authors have traced sharp discontinuities in distributions of species with respect to habitat structure by using presence/absence data alone. This approach appears to be sensitive to sampling of habitat types, and densities should be used wherever possible.     

Plant species richness in continental southern Siberia: effects of pH and climate in the context of the species pool hypothesis

Aim Many high‐latitude floras contain more calcicole than calcifuge vascular plant species. The species pool hypothesis explains this pattern through an historical abundance of high‐pH soils in the Pleistocene and an associated opportunity for the evolutionary accumulation of calcicoles. To obtain insights into the history of calcicole/calcifuge patterns, we studied species richness–pH–climate relationships across a climatic gradient, which included cool and dry landscapes resembling the Pleistocene environments of northern Eurasia. Location Western Sayan Mountains, southern Siberia. Methods Vegetation and environmental variables were sampled at steppe, forest and tundra sites varying in climate and soil pH, which ranged from 3.7 to 8.6. Species richness was related to pH and other variables using linear models and regression trees. Results Species richness is higher in areas with warmer winters and at medium altitudes that are warmer than the mountains and wetter than the lowlands. In treeless vegetation, the species richness–pH relationship is unimodal. In tundra vegetation, which occurs on low‐pH soils, richness increases with pH, but it decreases in steppes, which have high‐pH soils. In forests, where soils are more acidic than in the open landscape, the species richness–pH relationship is monotonic positive. Most species occur on soils with a pH of 6–7. Main conclusions Soil pH in continental southern Siberia is strongly negatively correlated with precipitation, and species richness is determined by the opposite effects of these two variables. Species richness increases with pH until the soil is very dry. In dry soils, pH is high but species richness decreases due to drought stress. Thus, the species richness–pH relationship is unimodal in treeless vegetation. Trees do not grow on the driest soils, which results in a positive species richness–pH relationship in forests. If modern species richness resulted mainly from the species pool effects, it would suggest that historically common habitats had moderate precipitation and slightly acidic to neutral soils.     

Herbaceous plant richness and vegetation cover in Mediterranean grasslands and shrublands

Different types of relationship between herbaceous species richness and several parameters indicating abundance of plant material (herbaceous, woody plants, litter and bare ground cover) are presented. The data were obtained from 50 sites along a 300 km strip running from E to W within Spain and Portugal. Each site was representative of the silvo-pastoral landscape of the Mediterranean type ecosystems of the Iberian peninsula, and contained two neighboring patches, one of grassland and the other of shrubland. 3,600 20 × 20 cm subplots were randomly located (72 per site, 36 per patch) crossing the boundary grassland/shrubland. This approach allowed us to analyze the richness-occupation relationship of the space from different points of view: among and within the sites, and among and within the grassland and shrubland plant communities. We found a unimodal relationship between richness-cover similar to the one generally accepted between richness and biomass. Our results show that the dependence of this relationship varies depending on the spatial scale of the analysis and on the type of data used. When the whole region is taken into account, significant unimodal relationships are found between richness and herbaceous cover, litter and bare ground, and a negative linear relationship with woody plant cover. Within the sites there are mainly linear or non-significant relationships. But the results also depend on the type of communities analyzed. In pastures, the unimodal relationship represents the combination of positive and negative linear responses for low and high cover values, respectively. The value for herbaceous cover in which maximum richness occurs is around 60%. In shrublands, this value for cover also corresponds to maximum species richness, although the possibilities of reaching it are limited by other variables, such as woody plant cover. This implies that, on not considering variability at local scale, the relationship is linear and positive. This paper shows the existence of a common model related to herbaceous cover, but this model has multiple controlling factors that act differently in each type of community.     

Race differences in pubic symphyseal aging patterns in the male

A well-documented multiracial sample of 704 male pubic bones allows for rigorous testing for racial differences in pubic symphyseal metamorphosis. The relationship between estimated age (using a modified Todd six-stage system) and age is examined as a function of race (White, Black, Mexican). One set of analyses incorporates linear regression models, while a second set does not impose such structure on the relationship. The latter analyses incorporate analysis of variance and related procedures. Significant differences in age are found across racial groups; it is seen that Blacks and Mexicans with advanced pubic symphyseal patterns tend to have lower ages than Whites. We do not address the question of causality, which may involve genetic factors and/or environmental variables such as diet, alcoholism, or drug abuse.     

Study of the relationship between sex pheromone trap catches of Lobesia botrana (Den. & Schiff.) (Lep., Tortricidae) and the accumulation of degree-days in Sherry vineyards (SW of Spain)

The relationship between temperature accumulations and pheromone trap captures of the males of Lobesia botrana (Den. & Schiff.) (Lep., Tortricidae) in the Sherry vineyards (SW of Spain) presents a statistically acceptable linear behaviour through conveniently transforming the variables. Data series ranging from 1990 to 1995 were used to compute the linear correlations. The reliability of the forecasts based on the resulting log-probit lines have shown to be acceptable in order to be considered as an useful tool to improve the effectiveness of the integrated pest management in the area.