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Information Criterion (information + criterion)
Kinds of Information Criterion Selected AbstractsRecruitment of burbot (Lota lota L.) in Lake Erie: an empirical modelling approachECOLOGY OF FRESHWATER FISH, Issue 3 2010M. A. Stapanian Stapanian MA, Witzel LD, Cook A. Recruitment of burbot (Lota lota L.) in Lake Erie: an empirical modelling approach. Ecology of Freshwater Fish 2010: 19: 326,337. Published 2010. This article is a US Government work and is in the public domain in the USA Abstract,,, World-wide, many burbot Lota lota (L.) populations have been extirpated or are otherwise in need of conservation measures. By contrast, burbot made a dramatic recovery in Lake Erie during 1993,2001 but declined during 2002,2007, due in part to a sharp decrease in recruitment. We used Akaike's Information Criterion to evaluate 129 linear regression models that included all combinations of one to seven ecological indices as predictors of burbot recruitment. Two models were substantially supported by the data: (i) the number of days in which water temperatures were within optimal ranges for burbot spawning and development combined with biomass of yearling and older (YAO) yellow perch Perca flavescens (Mitchill); and (ii) biomass of YAO yellow perch. Warmer winter water temperatures and increases in yellow perch biomass were associated with decreases in burbot recruitment. Continued warm winter water temperatures could result in declines in burbot recruitment, particularly in the southern part of the species' range. [source] Sex differences in genetic and environmental determinants of pulse pressureGENETIC EPIDEMIOLOGY, Issue 5 2006Katrina J. Scurrah Abstract Pulse pressure (PP) is an independent risk factor for cardiovascular disease. PP rises with age, more so in women. We examined sex differences in the correlations and variance components of PP in adult subjects from 767 nuclear families, enriched with those containing twins, from the Victorian Family Heart Study. After adjusting for age, we found no significant differences in the means or variances of PP in males and females. Under the assumption of no sex differences, the proportions of variance due to shared genes, shared environment, and individual-specific environment were 20%, 23% and 57%, respectively. However, same-sex relative pairs had significantly higher correlations than opposite-sex pairs (P=0.005), implying the existence of sex-dependent effects. Extensions to the simple variance components model suggested three possible explanations for these differences: smaller genetic correlation between opposite-sex pairs (,G,MF=0.45, P=0.007); smaller environmental correlation between opposite-sex pairs (P=0.0003); or different environmental and genetic correlations obtained by estimating genetic, environmental, and individual variance components separately for males and females (not nested, Akaike's Information Criterion (AIC) smaller by 6.69). Under the last model, the genetic component of PP variance is greater for males (1.62 vs 0.33) while the environmental component is greater for females (1.84 vs 0), which would have implications for the planning of gene discovery studies, since heritability would be higher in males. However, the second (environmental) approach best fits the data according to the AIC. Genetic explanations for sex differences in phenotypic correlations may be misleading unless shared environmental factors are also considered. PP illustrates a phenotype in which sex dependency represents an important component of phenotypic determination that can be revealed by detailed variance components modelling. Genet. Epidemiol. 2006. © 2006 Wiley-Liss, Inc. [source] Bayesian inference in a piecewise Weibull proportional hazards model with unknown change pointsJOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 4 2007J. Casellas Summary The main difference between parametric and non-parametric survival analyses relies on model flexibility. Parametric models have been suggested as preferable because of their lower programming needs although they generally suffer from a reduced flexibility to fit field data. In this sense, parametric survival functions can be redefined as piecewise survival functions whose slopes change at given points. It substantially increases the flexibility of the parametric survival model. Unfortunately, we lack accurate methods to establish a required number of change points and their position within the time space. In this study, a Weibull survival model with a piecewise baseline hazard function was developed, with change points included as unknown parameters in the model. Concretely, a Weibull log-normal animal frailty model was assumed, and it was solved with a Bayesian approach. The required fully conditional posterior distributions were derived. During the sampling process, all the parameters in the model were updated using a Metropolis,Hastings step, with the exception of the genetic variance that was updated with a standard Gibbs sampler. This methodology was tested with simulated data sets, each one analysed through several models with different number of change points. The models were compared with the Deviance Information Criterion, with appealing results. Simulation results showed that the estimated marginal posterior distributions covered well and placed high density to the true parameter values used in the simulation data. Moreover, results showed that the piecewise baseline hazard function could appropriately fit survival data, as well as other smooth distributions, with a reduced number of change points. [source] Incorporating movement into models of grey seal population dynamicsJOURNAL OF ANIMAL ECOLOGY, Issue 3 2006PHILIP J. HARRISON Summary 1One of the most difficult problems in developing spatially explicit models of population dynamics is the validation and parameterization of the movement process. We show how movement models derived from capture,recapture analysis can be improved by incorporating them into a spatially explicit metapopulation model that is fitted to a time series of abundance data. 2We applied multisite capture,recapture analysis techniques to photo-identification data collected from female grey seals at the four main breeding colonies in the North Sea between 1999 and 2001. The best-fitting movement models were then incorporated into state-space metapopulation models that explicitly accounted for demographic and observational stochasticity. 3These metapopulation models were fitted to a 20-year time series of pup production data for each colony using a Bayesian approach. The best-fitting model, based on the Akaike Information Criterion (AIC), had only a single movement parameter, whose confidence interval was 82% less than that obtained from the capture,recapture study, but there was some support for a model that included an effect of distance between colonies. 4The state-space modelling provided improved estimates of other demographic parameters. 5The incorporation of movement, and the way in which it was modelled, affected both local and regional dynamics. These differences were most evident as colonies approached their carrying capacities, suggesting that our ability to discriminate between models should improve as the length of the grey seal time series increases. [source] A model for the species,area,habitat relationshipJOURNAL OF BIOGEOGRAPHY, Issue 1 2003K. A. Triantis Abstract Aim, To propose a model (the choros model) for species diversity, which embodies number of species, area and habitat diversity and mathematically unifies area per se and habitat hypotheses. Location, Species richness patterns from a broad scale of insular biotas, both from island and mainland ecosystems are analysed. Methods, Twenty-two different data sets from seventeen studies were examined in this work. The r2 values and the Akaike's Information Criterion (AIC) were used in order to compare the quality of fit of the choros model with the Arrhenius species,area model. The classic method of log-log transformation was applied. Results, In twenty of the twenty-two cases studied, the proposed model gave a better fit than the classic species,area model. The values of z parameter derived from choros model are generally lower than those derived from the classic species,area equation. Main conclusions, The choros model can express the effects of area and habitat diversity on species richness, unifying area per se and the habitat hypothesis, which as many authors have noticed are not mutually exclusive but mutually supplementary. The use of habitat diversity depends on the specific determination of the ,habitat' term, which has to be defined based on the natural history of the taxon studied. Although the values of the z parameter are reduced, they maintain their biological significance as described by many authors in the last decades. The proposed model can also be considered as a stepping-stone in our understanding of the small island effect. [source] Extreme College Drinking and Alcohol-Related Injury RiskALCOHOLISM, Issue 9 2009Marlon P. Mundt Background:, Despite the enormous burden of alcohol-related injuries, the direct connection between college drinking and physical injury has not been well understood. The goal of this study was to assess the connection between alcohol consumption levels and college alcohol-related injury risk. Methods:, A total of 12,900 college students seeking routine care in 5 college health clinics completed a general Health Screening Survey. Of these, 2,090 students exceeded at-risk alcohol use levels and participated in a face-to-face interview to determine eligibility for a brief alcohol intervention trial. The eligibility interview assessed past 28-day alcohol use and alcohol-related injuries in the past 6 months. Risk of alcohol-related injury was compared across daily drinking quantities and frequencies. Logistic regression analysis and the Bayesian Information Criterion were applied to compute the odds of alcohol-related injury based on daily drinking totals after adjusting for age, race, site, body weight, and sensation seeking. Results:, Male college students in the study were 19% more likely (95% CI: 1.12,1.26) to suffer an alcohol-related injury with each additional day of consuming 8 or more drinks. Injury risks among males increased marginally with each day of consuming 5 to 7 drinks (odds ratio = 1.03, 95% CI: 0.94,1.13). Female participants were 10% more likely (95% CI: 1.04,1.16) to suffer an alcohol-related injury with each additional day of drinking 5 or more drinks. Males (OR = 1.69, 95% CI: 1.14,2.50) and females (OR = 1.81, 95% CI: 1.27,2.57) with higher sensation-seeking scores were more likely to suffer alcohol-related injuries. Conclusions:, College health clinics may want to focus limited alcohol injury prevention resources on students who frequently engage in extreme drinking, defined in this study as 8+M/5+F drinks per day, and score high on sensation-seeking disposition. [source] Effects of repeated burning on species richness in a Florida pine savanna: A test of the intermediate disturbance hypothesisJOURNAL OF VEGETATION SCIENCE, Issue 1 2000Brian Beckage Wunderlin (1982) except for Aristida beyrichiana; which follows Peet (1993). Vouchers for each species were collected and deposited at the University of Central Florida herbarium Abstract. We studied the effect of burning frequency on the density and species richness of understory flowering stems in a Florida sandhill. Flowering stems were censused weekly for 54 weeks in six sites that had been burned one to six times in the previous 16 years. We concurrently measured overstory characteristics such as species composition, density and basal area. We used maximum likelihood and Akaike's Information Criterion to compare linear, quadratic, saturating, and null models of community response to repeating burning. We did not find a relationship between species richness, diversity or flowering stem density and fire frequency. Tree density was related to fire frequency and may represent an indirect pathway for fire effects on understory characteristics. While we found no support for the Intermediate Disturbance Hypothesis, an analysis of our experimental design indicated that we had low statistical power. We develop the hypothesis that a saturating model of response to fire best describes understory species richness in our system. We test this hypothesis using the most extensive published fire data set we are aware of and find support for a saturating model. [source] Examining the extinction risk of specialized folivores: a comparative study of Colobine monkeysAMERICAN JOURNAL OF PRIMATOLOGY, Issue 9 2008Jason M. Kamilar Abstract Species extinctions are nonrandom with some taxa appearing to possess traits that increase their extinction risk. In this study, eight predictors of extinction risk were used as independent variables to predict the IUCN category of a subfamily of specialized folivorous primates, the Colobinae. All data were transformed into phylogenetically independent contrasts and were analyzed using bivariate regressions, multiple regression, and a maximum likelihood approach using Akaike's Information Criterion to assess model performance. Once an outlier was removed from the data set, species that devote a smaller proportion of their diet to mature leaf consumption appear to be at a greater risk of extinction. Also, as female body mass increases, so does extinction risk. In contrast, as maximum latitude and the number of habitat types increase, extinction risk appears to decrease. These findings emphasize the importance of examining detailed dietary variation for predicting extinction risk at a relatively fine taxonomic scale and, consequently, may help improve conservation management. Am. J. Primatol. 70:816,827, 2008. © 2008 Wiley-Liss, Inc. [source] Forecasting Models of Emergency Department CrowdingACADEMIC EMERGENCY MEDICINE, Issue 4 2009Lisa M. Schweigler MD Abstract Objectives:, The authors investigated whether models using time series methods can generate accurate short-term forecasts of emergency department (ED) bed occupancy, using traditional historical averages models as comparison. Methods:, From July 2005 through June 2006, retrospective hourly ED bed occupancy values were collected from three tertiary care hospitals. Three models of ED bed occupancy were developed for each site: 1) hourly historical average, 2) seasonal autoregressive integrated moving average (ARIMA), and 3) sinusoidal with an autoregression (AR)-structured error term. Goodness of fits were compared using log likelihood and Akaike's Information Criterion (AIC). The accuracies of 4- and 12-hour forecasts were evaluated by comparing model forecasts to actual observed bed occupancy with root mean square (RMS) error. Sensitivity of prediction errors to model training time was evaluated, as well. Results:, The seasonal ARIMA outperformed the historical average in complexity adjusted goodness of fit (AIC). Both AR-based models had significantly better forecast accuracy for the 4- and the 12-hour forecasts of ED bed occupancy (analysis of variance [ANOVA] p < 0.01), compared to the historical average. The AR-based models did not differ significantly from each other in their performance. Model prediction errors did not show appreciable sensitivity to model training times greater than 7 days. Conclusions:, Both a sinusoidal model with AR-structured error term and a seasonal ARIMA model were found to robustly forecast ED bed occupancy 4 and 12 hours in advance at three different EDs, without needing data input beyond bed occupancy in the preceding hours. [source] Variable Selection for Logistic Regression Using a Prediction-Focused Information CriterionBIOMETRICS, Issue 4 2006Gerda Claeskens Summary In biostatistical practice, it is common to use information criteria as a guide for model selection. We propose new versions of the focused information criterion (FIC) for variable selection in logistic regression. The FIC gives, depending on the quantity to be estimated, possibly different sets of selected variables. The standard version of the FIC measures the mean squared error of the estimator of the quantity of interest in the selected model. In this article, we propose more general versions of the FIC, allowing other risk measures such as the one based on Lp error. When prediction of an event is important, as is often the case in medical applications, we construct an FIC using the error rate as a natural risk measure. The advantages of using an information criterion which depends on both the quantity of interest and the selected risk measure are illustrated by means of a simulation study and application to a study on diabetic retinopathy. [source] Akaike's Information Criterion in Generalized Estimating EquationsBIOMETRICS, Issue 1 2001Wei Pan Summary. Correlated response data are common in biomedical studies. Regression analysis based on the generalized estimating equations (GEE) is an increasingly important method for such data. However, there seem to be few model-selection criteria available in GEE. The well-known Akaike Information Criterion (AIC) cannot be directly applied since AIC is based on maximum likelihood estimation while GEE is nonlikelihood based. We propose a modification to AIC, where the likelihood is replaced by the quasi-likelihood and a proper adjustment is made for the penalty term. Its performance is investigated through simulation studies. For illustration, the method is applied to a real data set. [source] Interpreting temporal variation in omnivore foraging ecology via stable isotope modellingFUNCTIONAL ECOLOGY, Issue 4 2009Carolyn M. Kurle Summary 1The use of stable carbon (C) and nitrogen (N) isotopes (,15N and ,13C, respectively) to delineate trophic patterns in wild animals is common in ecology. Their utility as a tool for interpreting temporal change in diet due to seasonality, migration, climate change or species invasion depends upon an understanding of the rates at which stable isotopes incorporate from diet into animal tissues. To best determine the foraging habits of invasive rats on island ecosystems and to illuminate the interpretation of wild omnivore diets in general, I investigated isotope incorporation rates of C and N in fur, liver, kidney, muscle, serum and red blood cells (RBC) from captive rats raised on a diet with low ,15N and ,13C values and switched to a diet with higher ,15N and ,13C values. 2I used the reaction progress variable method (RPVM), a linear fitting procedure, to estimate whether a single or multiple compartment model best described isotope turnover in each tissue. Small sample Akaike Information criterion (AICc) model comparison analysis indicated that 1 compartment nonlinear models best described isotope incorporation rates for liver, RBC, muscle, and fur, whereas 2 compartment nonlinear models were best for serum and kidney. 3I compared isotope incorporation rates using the RPVM versus nonlinear models. There were no differences in estimated isotope retention times between the model types for serum and kidney (except for N turnover in kidney from females). Isotope incorporation took longer when estimated using the nonlinear models for RBC, muscle, and fur, but was shorter for liver tissue. 4There were no statistical differences between sexes in the isotope incorporation rates. I also found that N and C isotope incorporation rates were decoupled for liver, with C incorporating into liver tissue faster than N. 5The data demonstrate the utility of analysing isotope ratios of multiple tissues from a single animal when estimating temporal variation in mammalian foraging ecology. [source] Aspects of the Armitage,Doll gamma frailty model for cancer incidence dataENVIRONMETRICS, Issue 3 2004Shizue Izumi Abstract Using solid cancer incidence data from atomic bomb survivors in Japan, we examine some aspects of the Armitage,Doll gamma frailty (ADF) model. We consider the following two interpretations for lack of fit of the Armitage,Doll multistage (AD) model found with cancer data: the AD type individual hazards are heterogeneous or the individual hazards increase more slowly with age than the AD type hazards. In order to examine these interpretations, we applied the ADF model and the modified AD model to radiation-related cancer incidence rates. We assessed the magnitude of frailty by a frailty parameter at the ADF model and departures from the AD-type baseline hazard by a shape increment parameter at the modified AD model. Akaike's information criterion (AIC) was used to examine the goodness of fit of the models. The modified AD model provided as good a fit as the ADF model. Our results support both interpretations and imply that these interpretations may be practically unidentifiable in univariate failure time data. Thus, results from the frailty model for univariate failure time data should be interpreted carefully. Copyright © 2004 John Wiley & Sons, Ltd. [source] Statistical issues on the determination of the no-observed-adverse-effect levels in toxicologyENVIRONMETRICS, Issue 4 2001Takashi Yanagawa Abstract The determination of a safe exposure level for toxic agents, often defined as the highest dose level with no toxic effect and termed the no-observed-adverse-effect level (NOAEL) is reviewed. The conventional methods based on statistical tests are criticized, particularly when the sample size is small, and an alternative method, which is based on the Akaike information criterion (AIC), is discussed. The method is extended to the estimation of the NOAEL for continuous data. Computer programs for Windows 95/NT for determining the NOAEL by the AIC approach are developed and its application to practical data is illustrated with examples. Copyright © 2001 John Wiley & Sons, Ltd. [source] Analyzing the Relationship Between Smoking and Coronary Heart Disease at the Small Area Level: A Bayesian Approach to Spatial ModelingGEOGRAPHICAL ANALYSIS, Issue 2 2006Jane Law We model the relationship between coronary heart disease and smoking prevalence and deprivation at the small area level using the Poisson log-linear model with and without random effects. Extra-Poisson variability (overdispersion) is handled through the addition of spatially structured and unstructured random effects in a Bayesian framework. In addition, four different measures of smoking prevalence are assessed because the smoking data are obtained from a survey that resulted in quite large differences in the size of the sample across the census tracts. Two of the methods use Bayes adjustments of standardized smoking ratios (local and global adjustments), and one uses a nonparametric spatial averaging technique. A preferred model is identified based on the deviance information criterion. Both smoking and deprivation are found to be statistically significant risk factors, but the effect of the smoking variable is reduced once the confounding effects of deprivation are taken into account. Maps of the spatial variability in relative risk, and the importance of the underlying covariates and random effects terms, are produced. We also identify areas with excess relative risk. [source] Physics-based GPS data inversion to estimate three-dimensional elastic and inelastic strain fieldsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2010Akemi Noda SUMMARY The Earth's crust is macroscopically treated as a linear elastic body, but it includes a number of defects. The occurrence of inelastic deformation such as brittle fracture at the defects brings about elastic deformation in the surrounding regions. The crustal deformation observed through geodetic measurements is the sum of the inelastic deformation as source and the elastic deformation as effect. On such a basic idea, we created a theory of physics-based strain analysis with general source representation by moment tensor, and developed an inversion method to separately estimate 3-D elastic and inelastic strain fields from GPS data. In this method, first, the optimum distribution of moment density tensor is determined from observed GPS data by using Akaike's information criterion. Then, the elastic and inelastic strain fields are obtained from the optimum moment tensor distribution by theoretical computation and direct conversion with elastic compliance tensor, respectively. We applied the inversion method to GPS horizontal velocity data, and succeeded in separately estimating 3-D elastic and inelastic strain rate fields in the Niigata,Kobe transformation zone, central Japan. As for the surface patterns of total strain, the present results of 3-D physics-based inversion analysis accord with the previous results of 2-D geometric inversion analysis. From the 3-D patterns of the inverted elastic and inelastic strain fields, we revealed that the remarkable horizontal contraction in the Niigata,Kobe transformation zone is elastic and restricted near the surface, but the remarkable shear deformation is inelastic and extends over the upper crust. [source] Global analysis of reptile elevational diversityGLOBAL ECOLOGY, Issue 4 2010Christy M. McCain ABSTRACT Aim, Latitudinal- and regional-scale studies of reptile diversity suggest a predominant temperature effect, unlike many other vertebrate richness patterns which tend to be highly correlated with both temperature and water variables. Here I examine montane gradients in reptile species richness with separate analyses of snakes and lizards from mountains around the world to assess a predominant temperature effect and three additional theories of diversity, including a temperature,water effect, the species,area effect and the mid-domain effect (MDE). Location, Twenty-five elevational gradients of reptile diversity from temperate, tropical and desert mountains in both hemispheres, spanning 10.3° N to 46.1° N. Methods, Elevational gradients in reptile diversity are based on data from the literature. Of the 63 data sets found or compiled, only those with a high, unbiased sampling effort were used in analyses. Twelve predictions and three interactions of diversity theory were tested using nonparametric statistics, linear regressions and multiple regression with the Akaike information criterion (AIC). Results, Reptile richness and, individually, snake and lizard richness on mountains followed four distinct patterns: decreasing, low-elevation plateaus, low-elevation plateaus with mid-elevation peaks, and mid-elevation peaks. Elevational reptile richness was most strongly correlated with temperature. The temperature effect was mediated by precipitation; reptile richness was more strongly tied to temperature on wet gradients than on arid gradients. Area was a secondary factor of importance, whereas the MDE was not strongly associated with reptile diversity on mountains. Main conclusions, Reptile diversity patterns on mountains did not follow the predicted temperature,water effect, as all diversity patterns were found on both wet and dry mountains. But the influence of precipitation on the temperature effect most likely reflects reptiles' use of radiant heat sources (sunning opportunities) that are more widespread on arid mountains than wet mountains due to lower humidity, sparser vegetation and less cloud cover across low and intermediate elevations. [source] Geographical and taxonomic influences on cranial variation in red colobus monkeys (Primates, Colobinae): introducing a new approach to ,morph' monkeysGLOBAL ECOLOGY, Issue 2 2009Andrea Cardini ABSTRACT Aim, To provide accurate but parsimonious quantitative descriptions of clines in cranial form of red colobus, to partition morphological variance into geographical, taxonomic and structured taxonomic components, and to visually summarize clines in multivariate shape data using a method which produces results directly comparable to both univariate studies of geographical variation and standard geometric morphometric visualization of shape differences along vectors. Location, Equatorial Africa. Methods, Sixty-four three-dimensional cranial landmarks were measured on 276 adult red colobus monkeys sampled over their entire distribution. Geometric morphometric methods were applied, and size and shape variables regressed onto geographical coordinates using linear and curvilinear models. Model selection was done using the second-order Akaike information criterion. Components of variation related to geography, taxon or their combined effect were partitioned using partial regresssion. Multivariate trends in clinal shape were summarized using principal components of predictions from regressions, plotting vector scores on maps as for univariate size, and visualizing differences along main axes of clinal shape variation using surface rendering. Results, Significant clinal variation was found in size and shape. Clines were similar in females and males. Trend surface analysis tended to be more accurate and parsimonious than alternative models in predicting morphology based on geography. Cranial form was relatively paedomorphic in East Africa and peramorphic in central Africa. Most taxonomic variation was geographically structured. However, taxonomic differences alone accounted for a larger proportion of total explained variance in shape (up to 40%) than in size (, 20%). Main conclusions, A strong cline explained most of the observed size variation and a significant part of the shape differences of red colobus crania. The pattern of geographical variation was largely similar to that previously reported in vervets, despite different habitat preferences (arboreal versus terrestrial) and a long period since divergence (c. 14,15 Myr). This suggests that some aspects of morphological divergence in both groups may have been influenced by similar environmental, geographical and historical factors. Cranial size is likely to be evolutionarily more labile and thus better reflects the influence of recent environmental changes. Cranial shape could be more resilient to change and thus better reflects phylogenetically informative differences. [source] Estimation Optimality of Corrected AIC and Modified Cp in Linear RegressionINTERNATIONAL STATISTICAL REVIEW, Issue 2 2006Simon L. Davies Summary Model selection criteria often arise by constructing unbiased or approximately unbiased estimators of measures known as expected overall discrepancies (Linhart & Zucchini, 1986, p. 19). Such measures quantify the disparity between the true model (i.e., the model which generated the observed data) and a fitted candidate model. For linear regression with normally distributed error terms, the "corrected" Akaike information criterion and the "modified" conceptual predictive statistic have been proposed as exactly unbiased estimators of their respective target discrepancies. We expand on previous work to additionally show that these criteria achieve minimum variance within the class of unbiased estimators. Résumé Les critères de modèle de sélection naissent souvent de la construction de mesures d'estimation impartiales, ou approximativement impartiales, connues comme divergences globales prévues. De telles mesures quantifient la disparité entre le vrai modèle (c'est-à-dire le modèle qui a produit les données observées) et un modèle candidat correspondant. En ce qui concerne les applications de régression linéaires contenant des erreurs distribuées normalement, le modèle de critère d'information "corrigé" Akaike et le modèle conceptuel de statistique de prévision "modifié" ont été proposés comme étant des instruments exacts de mesures d'estimation impartiales de leurs objectifs respectifs de divergences. En nous appuyant sur les travaux précédents et en les développant, nous proposons de démontrer, en outre, que ces critères réalisent une variance minimum au sein de la classe des instruments de mesures d'estimation impartiales. [source] Contributions of genetic and environmental components to changes in phenotypic variation between generationsJOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 4 2010A. Wolc Summary We evaluate the extent to which changes in phenotypic variation among generations of populations kept in the same environment are due to changes in genetic (VA) or in environmental (VE) variance. Data were available on body weight of adult poultry on a total of 89186 birds (mainly females) from six generations of each of seven lines of layers. There was substantial heterogeneity of variation between generations, shown to be in both VA and VE components. Based on the Akaike information criterion (AIC), the best fit was with both components changing, and a better fit was obtained if VA/VE (i.e. heritability) or VE, rather than VA, was assumed constant. In analyses of quantitative genetic data spanning environmental groups, attention should be paid to whether and how the variance components change among groups before undertaking detailed variance partition that may be sensitive to such changes. [source] Comparison of repeatability and multiple trait threshold models for litter size in sheep using observed and simulated data in Bayesian analysesJOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 4 2010W. Mekkawy Summary Bayesian analyses were used to estimate genetic parameters on 5580 records of litter size in the first four parities from 1758 Mule ewes. To examine the appropriateness of fitting repeatability (RM) or multiple trait threshold models (MTM) to litter size of different parities, both models were used to estimate genetic parameters on the observed data and were thereafter compared in a simulation study. Posterior means of the heritabilities of litter size in different parities using a MTM ranged from 0.12 to 0.18 and were higher than the heritability based on the RM (0.08). Posterior means of the genetic correlations between litter sizes of different parities were positive and ranged from 0.24 to 0.71. Data sets were simulated based on the same pedigree structure and genetic parameters of the Mule ewe population obtained from both models. The simulation showed that the relative loss in accuracy and increase in mean squared error (MSE) was substantially higher when using the RM, given that the parameters estimated from the observed data using the opposite model are the true parameters. In contrast, Bayesian information criterion (BIC) selected the RM as most appropriate model given the data because of substantial penalty for the higher number of parameters to be estimated in the MTM model. In conclusion, when the relative change in accuracy and MSE is of main interest for estimation of breeding values of litter size of different parities, the MTM is recommended for the given population. When reduction in risk of using the wrong model is the main aim, the BIC suggest that the RM is the most appropriate model. [source] Diffusion models for animals in complex landscapes: incorporating heterogeneity among substrates, individuals and edge behavioursJOURNAL OF ANIMAL ECOLOGY, Issue 5 2008John D. Reeve Summary 1Animals move commonly through a variety of landscape elements and edges in search of food, mates and other resources. We developed a diffusion model for the movement of an insect herbivore, the planthopper Prokelisia crocea, that inhabits a landscape composed of patches of its host plant, prairie cordgrass Spartina pectinata, embedded in a matrix of mudflat or smooth brome Bromus inermis. 2We used mark,release,resight experiments to quantify planthopper movements within cordgrass,brome and cordgrass,mudflat arenas. A diffusion model was then fitted that included varying diffusion rates for cordgrass and matrix, edge behaviour in the form of a biased random walk and heterogeneity among planthoppers (sessile vs. mobile). The model parameters were estimated by maximum likelihood using the numerical solution of the diffusion model as a probability density. Akaike's information criterion (AIC) values were used to compare models with different subsets of features. 3There was clear support for models incorporating edge behaviour and both sessile and mobile insects. The most striking difference between the cordgrass,brome and cordgrass,mudflat experiments involved edge behaviour. Planthoppers crossed the cordgrass,brome edge readily in either direction, but traversed the cordgrass,mudflat edge primarily in one direction (mudflat to cordgrass). Diffusion rates were also significantly higher on mudflat than for cordgrass and brome. 4The differences in behaviour for cordgrass,brome vs. cordgrass,mudflat edges have implications for the connectivity of cordgrass patches as well as their persistence. Higher dispersal rates are expected between cordgrass patches separated by brome relative to mudflat, but patches surrounded by mudflat appear more likely to persist through time. 5The experimental design and diffusion models used here could potentially be extended to any organism where mass mark,recapture experiments are feasible, as well as complex natural landscapes. [source] Ecological correlates of vulnerability to fragmentation in Neotropical batsJOURNAL OF APPLIED ECOLOGY, Issue 1 2008Christoph F. J. Meyer Summary 1In the face of widespread human-induced habitat fragmentation, identification of those ecological characteristics that render some species more vulnerable to fragmentation than others is vital for understanding, predicting and mitigating the effects of habitat alteration on biodiversity. We compare hypotheses on the causes of interspecific differences in fragmentation sensitivity using distribution and abundance data collected on 23 species of Neotropical bats. 2Bats were captured over a 2-year period on 11 land-bridge islands in Gatún Lake, Panama, and on the adjacent mainland. We derived a series of explanatory variables from our capture data and from the literature: (1) natural abundance in continuous forest, (2) body mass, (3) trophic level, (4) dietary specialization, (5) vertical stratification, (6) edge-sensitivity, (7) mobility, (8) wing morphology (aspect ratio and relative wing loading) and (9) ecologically scaled landscape indices (ESLIs). After phylogenetic correction, these variables were used separately and in combination to assess their association with two indices of fragmentation sensitivity, species prevalence (proportion of islands occupied) as well as an index of change in abundance. 3Model selection based on Akaike's information criterion identified edge-sensitivity as the best correlate of vulnerability to fragmentation. Natural abundance and mobility or traits linked to mobility (relative wing loading and ESLI) received limited support as predictors. Vulnerability of gleaning animalivorous bats is probably caused by a combination of these traits. 4Synthesis and applications. Our findings emphasize the importance of a local-scale approach in developing predictive models of species fragmentation sensitivity and indicate that risk assessments of Neotropical bats could be based on species tolerance to habitat edges and mobility-related traits. We suggest that, in order to be effective, management efforts should aim to minimize the amount of edge-habitat and reduce the degree of fragment-matrix contrast. Moreover, if high bat diversity is to be preserved in fragmented Neotropical landscapes, conservation measures regarding reserve design should assure spatial proximity to source populations in larger tracts of continuous forest and a low degree of remnant isolation. [source] Patterns of density, diversity, and the distribution of migratory strategies in the Russian boreal forest avifaunaJOURNAL OF BIOGEOGRAPHY, Issue 11 2008Russell Greenberg Abstract Aim, Comparisons of the biotas in the Palaearctic and Nearctic have focused on limited portions of the two regions. The purpose of this study was to assess the geographic pattern in the abundance, species richness, and importance of different migration patterns of the boreal forest avifauna of Eurasia from Europe to East Asia as well as their relationship to climate and forest productivity. We further examine data from two widely separated sites in the New World to see how these conform to the patterns found in the Eurasian system. Location, Boreal forest sites in Russia and Canada. Methods, Point counts were conducted in two to four boreal forest habitats at each of 14 sites in the Russian boreal forest from near to the Finnish border to the Far East, as well as at two sites in boreal Canada. We examined the abundance and species richness of all birds, and specific migratory classes, against four gradients (climate, primary productivity, latitude, and longitude). We tested for spatial autocorrelation in both dependent and independent variables using Moran's I to develop spatial correlograms. For each migratory class we used maximum likelihood to fit models, first assuming uncorrelated residuals and then assuming spatially autocorrelated residuals. For models assuming unstructured residuals we again generated correlograms on model residuals to determine whether model fitting removed spatial autocorrelation. Models were compared using Akaike's information criterion, adjusted for small sample size. Results, Overall abundance was highest at the eastern and western extremes of the survey region and lowest at the continent centre, whereas the abundance of tropical and short-distance migrants displayed an east,west gradient, with tropical migrants increasing in abundance in the east (and south), and short-distance migrants in the west. Although overall species richness showed no geographic pattern, richness within migratory classes showed patterns weaker than, but similar to, their abundance patterns described above. Overall abundance was correlated with climate variables that relate to continentality. The abundances of birds within different migration strategies were correlated with a second climatic gradient , increasing precipitation from west to east. Models using descriptors of location generally had greater explanatory value for the abundance and species-richness response variables than did those based on climate data and the normalized difference vegetation index (NDVI). Main conclusions, The distribution patterns for migrant types were related to both climatic and locational variables, and thus the patterns could be explained by either climatic regime or the accessibility of winter habitats, both historically and currently. Non-boreal wintering habitat is more accessible from both the western and eastern ends than from the centre of the boreal forest belt, but the tropics are most accessible from the eastern end of the Palaearctic boreal zone, in terms of distance and the absence of geographical barriers. Based on comparisons with Canadian sites, we recommend that future comparative studies between Palaearctic and Nearctic faunas be focused more on Siberia and the Russian Far East, as well as on central and western Canada. [source] Explaining the global pattern of protected area coverage: relative importance of vertebrate biodiversity, human activities and agricultural suitabilityJOURNAL OF BIOGEOGRAPHY, Issue 8 2008Colby Loucks Abstract Aim, Twelve per cent of the Earth's terrestrial surface is covered by protected areas, but neither these areas nor the biodiversity they contain are evenly distributed spatially. To guide future establishment of protected areas, it is important to understand the factors that have shaped the spatial arrangement of the current protected area system. We used an information-theoretic approach to assess the ability of vertebrate biodiversity measures, resource consumption and agricultural potential to explain the global coverage pattern of protected areas. Location, Global. Methods, For each of 762 World Wildlife Fund terrestrial ecoregions of the world, we measured protected area coverage, resource consumption, terrestrial vertebrate species richness, number of endemic species, number of threatened species, net primary production, elevation and topographic heterogeneity. We combined these variables into 39 a priori models to describe protected area coverage at the global scale, and for six biogeographical realms. Using the Akaike information criterion and Akaike weights, we identified the relative importance and influence of each variable in describing protected area coverage. Results, Globally, the number of endemic species was the best variable describing protected area coverage, followed by the number of threatened species. Species richness and resource consumption were of moderate importance and agricultural potential had weak support for describing protected area coverage at a global scale. Yet, the relative importance of these factors varied among biogeographical realms. Measures of vertebrate biodiversity (species richness, endemism and threatened species) were among the most important variables in all realms, except the Indo-Malayan, but had a wide range of relative importance and influence. Resource consumption was inversely related to protected area coverage across all but one realm (the Palearctic), most strongly in the Nearctic realm. Agricultural potential, despite having little support in describing protected area coverage globally, was strongly and positively related to protection in the Palearctic and Neotropical realms, as well as in the Indo-Malayan realm. The Afrotropical, Indo-Malayan and Australasian realms showed no clear, strong relationships between protected area coverage and the independent variables. Main conclusions, Globally, the existing protected area network is more strongly related to biodiversity measures than to patterns of resource consumption or agricultural potential. However, the relative importance of these factors varies widely among the world's biogeographical realms. Understanding the biases of the current protected area system may help to correct for them as future protected areas are added to the global network. [source] Patch occupancy of North American mammals: is patchiness in the eye of the beholder?JOURNAL OF BIOGEOGRAPHY, Issue 8 2003Robert K. Swihart Abstract Aim Intraspecific variation in patch occupancy often is related to physical features of a landscape, such as the amount and distribution of habitat. However, communities occupying patchy environments typically exhibit non-random distributions in which local assemblages of species-poor patches are nested subsets of assemblages occupying more species-rich patches. Nestedness of local communities implies interspecific differences in sensitivity to patchiness. Several hypotheses have been proposed to explain interspecific variation in responses to patchiness within a community, including differences in (1) colonization ability, (2) extinction proneness, (3) tolerance to disturbance, (4) sociality and (5) level of adaptation to prevailing environmental conditions. We used data on North American mammals to compare the performance of these ,ecological' hypotheses and the ,physical landscape' hypothesis. We then compared the best of these models against models that scaled landscape structure to ecologically relevant attributes of individual species. Location North America. Methods We analysed data on prevalence (i.e. proportion of patches occupied in a network of patches) and occupancy for 137 species of non-volant mammals and twenty networks consisting of four to seventy-five patches. Insular and terrestrial networks exhibited significantly different mean levels of prevalence and occupancy and thus were analysed separately. Indicator variables at ordinal and family levels were included in models to correct for effects caused by phylogeny. Akaike's information criterion was used in conjunction with ordinary least squares and logistic regression to compare hypotheses. Results A patch network's physical structure, indexed using patch area and isolation, received the greatest support among models predicting the prevalence of species on insular networks. Niche breadth (diet and habitat) received the greatest support for predicting prevalence of species occupying terrestrial networks. For both insular and terrestrial systems, physical features (patch area and isolation) received greater support than any of the ecological hypotheses for predicting species occupancy of individual patches. For terrestrial systems, scaling patch area by its suitability to a focal species and by individual area requirements of the species, and scaling patch isolation by species-specific dispersal ability and niche breadth, resulted in models of patch occupancy that were superior to models relying solely on physical landscape features. For all selected models, unexplained levels of variation were high. Main conclusions Stochasticity dominated the systems we studied, indicating that random events are probably quite important in shaping local communities. With respect to deterministic factors, our results suggest that forces affecting species prevalence and occupancy may differ between insular and terrestrial systems. Physical features of insular systems appeared to swamp ecological differences among species in determining prevalence and occupancy, whereas species with broad niches were disproportionately represented in terrestrial networks. We hypothesize that differential extinction over long time periods in highly variable networks has driven nestedness of mammalian communities on islands, whereas differential colonization over shorter time-scales in more homogeneous networks probably governed the local structure of terrestrial communities. Our results also demonstrate that integration of a species' ecological traits with physical features of a patch network is superior to reliance on either factor separately when attempting to predict the species' probability of patch occupancy in terrestrial systems. [source] Skew-normal linear calibration: a Bayesian perspectiveJOURNAL OF CHEMOMETRICS, Issue 8 2008Cléber da Costa Figueiredo Abstract In this paper, we present a Bayesian approach for estimation in the skew-normal calibration model, as well as the conditional posterior distributions which are useful for implementing the Gibbs sampler. Data transformation is thus avoided by using the methodology proposed. Model fitting is implemented by proposing the asymmetric deviance information criterion, ADIC, a modification of the ordinary DIC. We also report an application of the model studied by using a real data set, related to the relationship between the resistance and the elasticity of a sample of concrete beams. Copyright © 2008 John Wiley & Sons, Ltd. [source] Effects of a tropical cyclone on the distribution of hatchery-reared black-spot tuskfish Choerodon schoenleinii determined by acoustic telemetryJOURNAL OF FISH BIOLOGY, Issue 3 2010Y. Kawabata The effects of a tropical cyclone on the distribution of hatchery-reared black-spot tuskfish Choerodon schoenleinii were examined using acoustic telemetry. Nine fish were released in Urasoko Bay, Ishigaki Island, Japan, in September 2006, and another nine were released in June to July 2007, before a cyclone's passing through the area in September 2007. Data for the fish released in 2006 were used as the cyclone-inexperienced group to compare their distribution pattern to that of the 2007 cyclone-experienced group. Both groups of fish were monitored for up to 150 days. Of the nine fish in each group, four (44%) and two (22%) were monitored for over 150 days in the cyclone-inexperienced and the cyclone-experienced groups, respectively. Three of the five fish that had settled in the monitoring area left the area within a few days of the cyclone event. To estimate the time of disappearance of the fish, maximum wind speed during a period of 7 days (indicating the occurrence and intensity of the tropical cyclone), fish size and release year were evaluated as explanatory variables using a Cox proportional hazards model with Akaike's information criterion. The best predictive model included the effect of maximum wind speed. One fish that left the monitoring area displayed movement patterns related to strong winds, suggesting that wind-associated strong currents swept the fish away. No relationships were found between the movement patterns of the other two fish and any physical environmental data. The daily detection periods of one of the two fish gradually decreased after the cyclone hit, and this fish eventually left the monitoring area within 3 days, suggesting that it shifted to a habitat outside the monitoring area. These results indicate that tropical cyclones have both direct and indirect effects on the distribution of hatchery-reared C. schoenleinii. [source] Related-variables selection in temporal disaggregationJOURNAL OF FORECASTING, Issue 4 2009Kosei Fukuda Abstract Two related-variables selection methods for temporal disaggregation are proposed. In the first method, the hypothesis tests for a common feature (cointegration or serial correlation) are first performed. If there is a common feature between observed aggregated series and related variables, the conventional Chow,Lin procedure is applied. In the second method, alternative Chow,Lin disaggregating models with and without related variables are first estimated and the corresponding values of the Bayesian information criterion (BIC) are stored. It is determined on the basis of the selected model whether related variables should be included in the Chow,Lin model. The efficacy of these methods is examined via simulations and empirical applications. Copyright © 2008 John Wiley & Sons, Ltd. [source] Comparing density forecast models,JOURNAL OF FORECASTING, Issue 3 2007Yong Bao Abstract In this paper we discuss how to compare various (possibly misspecified) density forecast models using the Kullback,Leibler information criterion (KLIC) of a candidate density forecast model with respect to the true density. The KLIC differential between a pair of competing models is the (predictive) log-likelihood ratio (LR) between the two models. Even though the true density is unknown, using the LR statistic amounts to comparing models with the KLIC as a loss function and thus enables us to assess which density forecast model can approximate the true density more closely. We also discuss how this KLIC is related to the KLIC based on the probability integral transform (PIT) in the framework of Diebold et al. (1998). While they are asymptotically equivalent, the PIT-based KLIC is best suited for evaluating the adequacy of each density forecast model and the original KLIC is best suited for comparing competing models. In an empirical study with the S&P500 and NASDAQ daily return series, we find strong evidence for rejecting the normal-GARCH benchmark model, in favor of the models that can capture skewness in the conditional distribution and asymmetry and long memory in the conditional variance.,,Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||