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Model Fit (model + fit)
Selected AbstractsAssessing autonomic symptoms of Parkinson's disease with the SCOPA-AUT: a new perspective from Rasch analysisEUROPEAN JOURNAL OF NEUROLOGY, Issue 2 2010M. J. Forjaz Background:, The Scale for Outcomes in Parkinson's disease (PD) for Autonomic Symptoms (SCOPA-AUT) is a specific scale to assess autonomic dysfunction in PD patients. It was developed and validated under the classic test theory approach. This study sought to test whether the SCOPA-AUT meets item response theory standards for reliability, internal construct validity, response category ordering, and differential item functioning by gender and age group. Method:, The Rasch measurement model was applied to a sample of 385 PD patients. Results:, Model fit was obtained after the response categories were rescored and item 10-Incomplete emptying deleted because of redundancy. Person separation index, a reliability measure, was 0.82. All but two items (2-Sialorrhea and 13-Nocturia) were free of gender- and age-related bias. The strict tests of unidimensionality were met, indicating the validity of the total sumscore. Scale targeting suggested the need for items representing milder autonomic symptoms. Conclusions:, Suggestions for improving the SCOPA-AUT include a shorter scale with a simpler response scheme and a combination of sexual items for men and women. The resulting SCOPA-AUT is a reliable scale, with good internal construct validity, providing Rasch transformed results on a linear metric scale. [source] The rapid spread of invasive Eurasian Collared Doves Streptopelia decaocto in the continental USA follows human-altered habitatsIBIS, Issue 3 2010IKUKO FUJISAKI Understanding factors related to the range expansion trajectory of a successful invasive species may provide insights into environmental variables that favour additional expansion or guide monitoring and survey efforts for this and other invasive species. We examined the relationship of presence and abundance of Eurasian Collared Doves Streptopelia decaocto to environmental factors using recent data from the North American Breeding Bird Survey to understand factors influencing its expansion into the continental USA. A zero-inflated Poisson (ZIP) model was used to account for excess zero observations because this species was not observed on the majority of survey routes, despite its large geographical range. Model fit was improved when we included environmental covariates as compared with the null model, which only included distance from the route where this species was first observed. Probability of zero count was positively related to the distance from the first route and road density and was inversely related to minimum temperature and distance to coast. Abundance of the species was positively related to road density and was inversely related to annual precipitation and distance to coast. Random intercept by land-cover type also improved model fit. Model fit was improved with the ZIP model over the standard Poisson model, suggesting that presence and abundance of this species are characterized by different environmental factors. However, overall low accuracy of model-predicted presence/absence and abundance with the independent validation dataset may indicate either that there are other explanatory factors or that there is great uncertainty in the species' colonization process. Our large-scale study provides additional evidence that the range expansion of this species tends to follow human-altered landscapes such as road and agricultural areas as well as responding to general geographical features such as coastlines or thermal clines. Such patterns may hold true for other invasive species and may provide guidelines for monitoring and assessment activities in other invasive taxa. [source] Statistical analyses of freeway traffic flowsJOURNAL OF FORECASTING, Issue 1 2002Claudia Tebaldi Abstract This paper concerns the exploration of statistical models for the analysis of observational freeway flow data, and the development of empirical models to capture and predict short-term changes in traffic flow characteristics on sequences of links in a partially detectorized freeway network. A first set of analyses explores regression models for minute-by-minute traffic flows, taking into account time of day, day of the week, and recent upstream detector-based flows. Day- and link-specific random effects are used in a hierarchical statistical modelling framework. A second set of analyses captures day-specific idiosyncrasies in traffic patterns by including parameters that may vary throughout the day. Model fit and short-term predictions of flows are thus improved significantly. A third set of analyses includes recent downstream flows as additional predictors. These further improvements, though marginal in most cases, can be quite radically useful in cases of very marked breakdown of freeway flows on some links. These three modelling stages are described and developed in analyses of observational flow data from a set of links on Interstate Highway 5 (I-5) near Seattle. Copyright © 2002 John Wiley & Sons, Ltd. [source] Factors Associated With Positive D-dimer Results in Patients Evaluated for Pulmonary EmbolismACADEMIC EMERGENCY MEDICINE, Issue 6 2010Christopher Kabrhel MD Abstract Objectives:, Available D-dimer assays have low specificity and may increase radiographic testing for pulmonary embolism (PE). To help clinicians better target testing, this study sought to quantify the effect of risk factors for a positive quantitative D-dimer in patients evaluated for PE. Methods:, This was a prospective, multicenter, observational study. Emergency department (ED) patients evaluated for PE with a quantitative D-dimer were eligible for inclusion. The main outcome of interest was a positive D-dimer. Odds ratio (ORs) and 95% confidence intervals (CIs) were determined by multivariable logistic regression. Adjusted estimates of relative risk were also calculated. Results:, A total of 4,346 patients had D-dimer testing, of whom 2,930 (67%) were women. A total of 2,500 (57%) were white, 1,474 (34%) were black or African American, 238 (6%) were Hispanic, and 144 (3%) were of other race or ethnicity. The mean (±SD) age was 48 (±17) years. Overall, 1,903 (44%) D-dimers were positive. Model fit was adequate (c-statistic = 0.739, Hosmer and Lemeshow p-value = 0.13). Significant positive predictors of D-dimer positive included female sex; increasing age; black (vs. white) race; cocaine use; general, limb, or neurologic immobility; hemoptysis; hemodialysis; active malignancy; rheumatoid arthritis; lupus; sickle cell disease; prior venous thromboembolism (VTE; not under treatment); pregnancy and postpartum state; and abdominal, chest, orthopedic, or other surgery. Warfarin use was protective. In contrast, several variables known to be associated with PE were not associated with positive D-dimer results: body mass index (BMI), estrogen use, family history of PE, (inactive) malignancy, thrombophilia, trauma within 4 weeks, travel, and prior VTE (under treatment). Conclusions:, Many factors are associated with a positive D-dimer test. The effect of these factors on the usefulness of the test should be considered prior to ordering a D-dimer. ACADEMIC EMERGENCY MEDICINE 2010; 17:589,597 © 2010 by the Society for Academic Emergency Medicine [source] Speed, Accuracy, and Serial Order in Sequence ProductionCOGNITIVE SCIENCE - A MULTIDISCIPLINARY JOURNAL, Issue 1 2007Peter Q. Pfordresher The production of complex sequences like music or speech requires the rapid and temporally precise production of events (e.g., notes and chords), often at fast rates. Memory retrieval in these circumstances may rely on the simultaneous activation of both the current event and the surrounding context (Lashley, 1951). We describe an extension to a model of incremental retrieval in sequence production (Palmer & Pfordresher, 2003) that incorporates this logic to predict overall error rates and speed,accuracy trade-offs, as well as types of serial ordering errors. The model,assumes that retrieval of the current event is influenced by activations of surrounding events. Activations of surrounding events increase over time, such that both the accessibility of distant events and overall accuracy increases at slower production rates. The model's predictions were tested in an experiment in which pianists performed unfamiliar music at 8 different tempi. Model fits to speed,accuracy data and to serial ordering errors support model predictions. Parameter fits to individual data further suggest that working memory contributes to the retrieval of serial order and overall accuracy is influenced in addition by motor dexterity and domain-specific skill. [source] Differences in the measured alcohol content of drinks between black, white and Hispanic men and women in a US national sampleADDICTION, Issue 9 2009William C. Kerr ABSTRACT Aims To measure and describe drink alcohol content differences between Hispanic, non-Hispanic white and non-Hispanic black men and women in the United States. Design A telephone survey re-interview of 397 respondents who participated originally in the 2005 National Alcohol Survey, of whom 306 provided complete information on home drinks. Setting United States. Participants Adults aged 18 years and older from across the United States. Measurements Direct measurement by respondents of simulated drink pours in respondents' own glassware using a provided beaker and reported beverage brands were used to calculate drink alcohol content. Findings Black men were found to have the largest overall mean drink alcohol content at 0.79 oz (23 ml) of alcohol. This was significantly larger than the mean for white men or for black women and added 30% to black men's monthly alcohol intake when applied to their reported number of drinks. Spirits drinks were found to be particularly large for men. Multivariate models indicated that drink alcohol content differences are attributable more to income and family structure differences than to unmeasured cultural factors tied to race or ethnicity per se. Models predicting alcohol-related consequences and dependence indicate that adjusting drink alcohol content improves model fit and reduces differences between race/ethnicity defined groups. Conclusions Differences in drink alcohol content by gender, race/ethnicity and beverage type choice should be considered in comparisons of drinking patterns and alcohol-related outcomes. Observed differences can be explained partially by measured characteristics regarding family structure and income. [source] The impact of a social network intervention on retention in Belgian therapeutic communities: a quasi-experimental studyADDICTION, Issue 7 2006Veerle Soyez ABSTRACT Background Although numerous studies recognize the importance of social network support in engaging substance abusers into treatment, there is only limited knowledge of the impact of network involvement and support during treatment. The primary objective of this research was to enhance retention in Therapeutic Community treatment utilizing a social network intervention. Aims The specific goals of this study were (1) to determine whether different pre-treatment factors predicted treatment retention in a Therapeutic Community; and (2) to determine whether participation of significant others in a social network intervention predicted treatment retention. Design, setting and participants Consecutive admissions to four long-term residential Therapeutic Communities were assessed at intake (n = 207); the study comprised a mainly male (84.9%) sample of polydrug (41.1%) and opiate (20.8%) abusers, of whom 64.4% had ever injected drugs. Assessment involved the European version of the Addiction Severity Index (EuropASI), the Circumstances, Motivation, Readiness scales (CMR), the Dutch version of the family environment scale (GKS/FES) and an in-depth interview on social network structure and perceived social support. Network members of different cohorts were assigned to a social network intervention, which consisted of three elements (a video, participation at an induction day and participation in a discussion session). Findings Hierarchical regression analyses showed that client-perceived social support (F1,198 = 10.9, P = 0.001) and treatment motivation and readiness (F1,198 = 8.8; P = 0.003) explained a significant proportion of the variance in treatment retention (model fit: F7,197 = 4.4; P = 0.000). By including the variable ,significant others' participation in network intervention' (network involvement) in the model, the fit clearly improved (F1,197 = 6.2; P = 0.013). At the same time, the impact of perceived social support decreased (F1,197 = 2.9; P = 0.091). Conclusions Participation in the social network intervention was associated with improved treatment retention controlling for other client characteristics. This suggests that the intervention may be of benefit in the treatment of addicted individuals. [source] Understanding and using the implicit association test: V. measuring semantic aspects of trait self-conceptsEUROPEAN JOURNAL OF PERSONALITY, Issue 8 2008Konrad Schnabel Abstract Implicit Association Tests (IATs) often reveal strong associations of self with positive rather than negative attributes. This poses a problem in using the IAT to measure associations involving traits with either positive or negative evaluative content. In two studies, we employed non-bipolar but evaluatively balanced Big Five traits as attribute contrasts and explored correlations of IATs with positive (e.g. sociable vs. conscientious) or negative (e.g. reserved vs. chaotic) attributes. Results showed (a) satisfactory internal consistencies for all IATs, (b) explicit,explicit and implicit,implicit correlations that were moderate to high and comparable in strength after both were corrected for attenuation and (c) better model fit for latent variable models that linked the implicit and explicit measures to distinct latent factors rather to the same factor. Together, the results suggest that IATs can validly assess the semantic aspect of trait self-concepts and that implicit and explicit self-representations are, although correlated, also distinct constructs. Copyright © 2008 John Wiley & Sons, Ltd. [source] Assessment of Family Functioning in Caucasian and Hispanic Americans: Reliability, Validity, and Factor Structure of the Family Assessment DeviceFAMILY PROCESS, Issue 4 2007GREGORY A. AARONS PH.D. The purpose of this study was to examine the factor structure, reliability, and validity of the Family Assessment Device (FAD) among a national sample of Caucasian and Hispanic American families receiving public sector mental health services. A confirmatory factor analysis conducted to test model fit yielded equivocal findings. With few exceptions, indices of model fit, reliability, and validity were poorer for Hispanic Americans compared with Caucasian Americans. Contrary to our expectation, an exploratory factor analysis did not result in a better fitting model of family functioning. Without stronger evidence supporting a reformulation of the FAD, we recommend against such a course of action. Findings highlight the need for additional research on the role of culture in measurement of family functioning. [source] Separation of intrinsic and scattering seismic attenuation in the Southern Apennine zone, ItalyGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2002F. Bianco Summary Scattered waves observed at the seismographs of the National Italy's seismic network have been used to investigate the intrinsic dissipation and scattering properties of the lithosphere under the Southern Apennines, Italy. First, we investigate the coda-Q properties, then we apply the MLTW analysis in the hypothesis of velocity and scattering coefficient constant with depth, and finally we interpret these results with the aid of numerical simulations in a medium with depth dependent velocity and scattering coefficient. Results obtained in the hypothesis of a uniform model show that a low scattering-Q,1 and a relatively higher intrinsic-Q,1 characterize the lithosphere of the Southern Apennines. Numerical simulations of the seismogram energy envelopes were performed hypothesizing a strongly scattering crust and trasparent upper mantle, both with reasonable intrinsic dissipation coefficients. In these symplifying assumptions the theoretical curves calculated for the homogeneous model fit to the synthetic envelopes with scattering attenuation coefficients always greater than the synthetic values. This results lead to the consideration that scattering-Q,1 obtained using MLTW analysis under the assumption of uniform medium are overestimated. The values of the scattering-Q,1 estimated for Apennines at low frequency (1,2 Hz) in the hypothesis of uniform medium are of the same order of those obtained in several areas around the world. The estimates obtained for frequencies ranging from 2 to 12 Hz are very low if compared with those obtained in the same hypothesis for other areas around the world. Coda Q,1 closely resembles intrinsic Q,1. [source] Organic carbon and carbon isotopes in modern and 100-year-old-soil archives of the Russian steppeGLOBAL CHANGE BIOLOGY, Issue 10 2002Margaret S. Torn Abstract Archived soils can provide valuable information about changes in the carbon and carbon isotope content of soils during the past century. We characterized soil carbon dynamics in a Russian steppe preserve using a 100-year-old-soil archive and modern samples collected from the same site. The site has been protected since 1885 to the present, during which time the region has experienced widespread conversion to cultivation, a decrease in fire frequency, and a trend of increasing precipitation. In the preserve, the amount of organic carbon did not change appreciably between the 1900 and 1997 sampling dates, with 32 kg C/m2 in the top meter and a third of that in the top 20 cm. Carbon and nitrogen stocks varied by less than 6% between two replicate modern soil pits or between the modern sites and the archive. Radiocarbon content decreased with depth in all sites and the modern SOM had positive , values near the surface due to nuclear weapons testing in the early 1960s. In the upper 10 cm, most of the SOM had a turnover time of 6,10 years, according to a model fit to the radiocarbon content. Below about 10 cm, the organic matter was almost all passive material with long (millennial) turnover times. Soil respiration ,14CO2 on a summer day was 106,109,, an isotopic disequilibrium of about 9, relative to atmospheric 14CO2. In both the modern and archive soil, the relative abundance of 13C in organic matter increased with depth by 2, in the upper meter from ,13C = --26, at 5 cm to --24, below a meter. In addition, the slope of ,13C vs. depth below 5 cm was the same for both soils. Given the age of the soil archive, these results give clear evidence that the depth gradients are not due to depletion of atmospheric 13CO2 by fossil fuel emissions but must instead be caused by isotopic fractionation between plant litter inputs and preservation of SOM. Overall, the data show that these soils have a large reservoir of recalcitrant C and stocks had not changed between sampling dates 100 years apart. [source] Patient preferences for managing asthma: results from a discrete choice experimentHEALTH ECONOMICS, Issue 7 2007Madeleine T. King Abstract Effective control of asthma requires regular preventive medication. Poor medication adherence suggests that patient preferences for medications may differ from the concerns of the prescribing clinicians. This study investigated patient preferences for preventive medications across symptom control, daily activities, medication side-effects, convenience and costs, using a discrete choice experiment embedded in a randomized clinical trial involving patients with mild,moderate persistent asthma. The present data were collected after patients had received 6 weeks' treatment with one of two drugs. Three choice options were presented, to continue with the current drug, to change to an alternative, hypothetical drug, or to take no preventive medication. Analysis used random parameter multinomial logit. Most respondents chose to continue with their current drug in most choice situations but this tendency differed depending on which medication they had been allocated. Respondents valued their ability to participate in usual daily activities and sport, preferred minimal symptoms, and were less likely to choose drugs with side-effects. Cost was also significant, but other convenience attributes were not. Demographic characteristics did not improve the model fit. This study illustrates how discrete choice experiments may be embedded in a clinical trial to provide insights into patient preferences. Copyright © 2007 John Wiley & Sons, Ltd. [source] Testing effective connectivity changes with structural equation modeling: What does a bad model tell us?HUMAN BRAIN MAPPING, Issue 12 2006Andrea B. Protzner Abstract Structural equation modeling (SEM) is a statistical method that can assess changes in effective connectivity across tasks or between groups. In its initial application to neuroimaging data, anatomical connectivity provided the constraints to decompose interregional covariances to estimate effective connections. There have been concerns expressed, however, with the validity of interpreting effective connections for a model that does not adequately fit the data. We sought to address this concern by creating two population networks with different patterns of effective connectivity, extracting three samples sizes (N = 100, 60, 20), and then assessing whether the ability to detect effective connectivity differences depended on absolute model fit. Four scenarios were assessed: (1) elimination of a region showing no task differences; (2) elimination of connections with no task differences; (3) elimination of connections that carried task differences, but could be expressed through alternative indirect routes; (4) elimination of connections that carried task differences, and could not be expressed through indirect routes. We were able to detect task differences in all four cases, despite poor absolute model fit. In scenario 3, total effects captured the overall task differences even though the direct effect was no longer present. In scenario 4, task differences that were included in the model remained, but the missing effect was not expressed. In conclusion, it seems that when independent information (e.g., anatomical connectivity) is used to define the causal structure in SEM, inferences about task- or group-dependent changes are valid regardless of absolute model fit. Hum Brain Mapp, 2006. © 2006 Wiley-Liss, Inc. [source] The effect of learning organization culture on the relationship between interpersonal trust and organizational commitmentHUMAN RESOURCE DEVELOPMENT QUARTERLY, Issue 2 2009Ji Hoon Song The primary purpose of this research was to assess the effect of learning organization culture on the linkage between interpersonal trust and organizational commitment. The study sample was obtained from employees of two major Korean conglomerates. Online questionnaires were completed by 321 respondents. Structural equation modeling (SEM) was used to detect the effects of learning organization culture on the basis of the model fit to data comparisons and the significance of path coefficient estimates in the hypothesized model. The results suggest that learning organization culture works as a mediating variable to explain the association between interpersonal trust and organizational commitment. Recommendations for future research and implications for human resource development research and practice are discussed. [source] Suspended sediment dynamics in a steep, glacier-fed mountain stream, Place Creek, CanadaHYDROLOGICAL PROCESSES, Issue 9 2003G. Richards Abstract This study examined suspended sediment concentration (SSC) during the ablation seasons of 2000 and 2001 in Place Creek, Canada, a steep, glacier-fed mountain stream. Comparison of stream flow in Place Creek with that in an adjacent, almost unglacierized catchment provided a rational basis for separating the ablation seasons into nival, nival,glacial, glacial and autumn recession subseasons. Distinct groupings of points in plots of electrical conductivity against discharge supported the validity of the subseasonal divisions in terms of varying hydrological conditions. Relationships between SSC and discharge (Q) varied between the two study seasons, and between subseasons. Hysteresis in the SSC,Q relationship was evident at both event and weekly time-scales. Some suspended sediment released from pro-glacial Place Lake (the source of Place Creek) appeared to be lost to channel storage at low flows, especially early in the ablation season, with re-entrainment at higher flows. Multiple regression models were derived for the subseasons using predictor variables including Q, Q2, the change in Q over the previous 3 h, cumulative discharge over the ablation season, total precipitation over the previous 24 h and SSC measured at 1500 hours as an index value for each day. The models produced adjusted R2 values ranging from 0·71 to 0·91, and provided tentative insights into the differences in SSC dynamics amongst subseasons. Introduction of the index value of SSC significantly improved the model fit during the nival,glacial and glacial subseasons for both years, as it adjusts the model to the current condition of sediment supply. Copyright © 2003 John Wiley & Sons, Ltd. [source] Winter streamflow variability, Yukon Territory, CanadaHYDROLOGICAL PROCESSES, Issue 4 2002R. D. Moore Abstract Knowledge of winter streamflow regimes is required in northern catchments to evaluate water supply and to assess the vulnerability of aquatic habitat. The objective of this study was to explore the nature and causes of winter streamflow variability in northern rivers through examination of a limited number of case studies involving intensive field measurements, as well as a synoptic analysis of winter streamflow measurements archived by Water Survey of Canada for rivers in Yukon Territory, Canada. Evidence was found for an abrupt decrease in discharge at freeze-up in one of the case studies and for 10 of the 25 stations in the synoptic analysis that had measurements within 30 days of freeze-up (an additional 12 stations had no measurements within 30 days of freeze-up). However, given the paucity of measurements in the early winter, the magnitude, duration and frequency of these events cannot be specified. The case studies indicate that, even where a coherent depression does not occur, discharge can fluctuate around a smooth recession trend for about the first 30 days after the onset of ice effects, probably as a result of transient storage and release of water behind ice jams. A storage-depletion model that represents streamflow as outflow from two parallel linear reservoirs provided a reasonable fit to most of the observed measurements (excluding those in the first 30 days following freeze-up), with model fit deteriorating with increasing latitude and decreasing catchment size. The effect of latitude could relate to abstraction of flow by ice production, which would cause deviations from a storage-depletion trend. Northern catchments also tended to have steeper late-winter recessions, which could reflect a lack of extensive, deep aquifers to maintain late-winter discharge. The tendency to poorer model fit in smaller catchments could reflect a problem with data reliability, since it is more difficult to find good winter gauging sections in smaller streams. Some evidence for temperature-related discharge fluctuations was found in both the case studies and synoptic analyses. However, the magnitude of these effects appears to be about ±10 to 15%, at most, and not to be consistent between winters. Further advances in understanding winter streamflow variability will require frequent measurements on a range of streams over a number of winters. Copyright © 2002 John Wiley & Sons, Ltd. [source] The rapid spread of invasive Eurasian Collared Doves Streptopelia decaocto in the continental USA follows human-altered habitatsIBIS, Issue 3 2010IKUKO FUJISAKI Understanding factors related to the range expansion trajectory of a successful invasive species may provide insights into environmental variables that favour additional expansion or guide monitoring and survey efforts for this and other invasive species. We examined the relationship of presence and abundance of Eurasian Collared Doves Streptopelia decaocto to environmental factors using recent data from the North American Breeding Bird Survey to understand factors influencing its expansion into the continental USA. A zero-inflated Poisson (ZIP) model was used to account for excess zero observations because this species was not observed on the majority of survey routes, despite its large geographical range. Model fit was improved when we included environmental covariates as compared with the null model, which only included distance from the route where this species was first observed. Probability of zero count was positively related to the distance from the first route and road density and was inversely related to minimum temperature and distance to coast. Abundance of the species was positively related to road density and was inversely related to annual precipitation and distance to coast. Random intercept by land-cover type also improved model fit. Model fit was improved with the ZIP model over the standard Poisson model, suggesting that presence and abundance of this species are characterized by different environmental factors. However, overall low accuracy of model-predicted presence/absence and abundance with the independent validation dataset may indicate either that there are other explanatory factors or that there is great uncertainty in the species' colonization process. Our large-scale study provides additional evidence that the range expansion of this species tends to follow human-altered landscapes such as road and agricultural areas as well as responding to general geographical features such as coastlines or thermal clines. Such patterns may hold true for other invasive species and may provide guidelines for monitoring and assessment activities in other invasive taxa. [source] A French adaptation of the Infant,Toddler Social and Emotional AssessmentINFANT MENTAL HEALTH JOURNAL, Issue 2 2004Ziva Bracha This article presents the psychometric properties of the French adaptation of the Infant,Toddler Social and Emotional Assessment (ITSEA), named the Evaluation Sociale et Emotionelle de Jeunes Enfants (ESEJE). The French adaptation involved translation and backtranslation and was administered to 179 parents in pediatric well-baby centers and 115 parents in childcare centers. Confirmatory factor analyses were employed to assess for latent factor structure, and model fit was assessed using three standard-fit indices. Analysis of variance examined age and gender effects on mean domain and scale scores. Confirmatory factor analyses supported a comparable latent factor structure to that reported for the ITSEA. All domains and most scales show adequate intrascale reliability. Certain age and gender effects on mean score differed from those reported for the U.S. sample. Our preliminary results indicate that the ESEJE shares the same latent factor structure as its English counterpart and may be a promising tool for the early detection of problem behaviors and delays in the acquisition of competencies in a French population. ©2004 Michigan Association for Infant Mental Health. [source] Use of resampling to select among alternative error structure specifications for GLMM analyses of repeated measurements,INTERNATIONAL JOURNAL OF METHODS IN PSYCHIATRIC RESEARCH, Issue 1 2004Scott Tonidandel Abstract Autocorrelated error and missing data due to dropouts have fostered interest in the flexible general linear mixed model (GLMM) procedures for analysis of data from controlled clinical trials. The user of these adaptable statistical tools must, however, choose among alternative structural models to represent the correlated repeated measurements. The fit of the error structure model specification is important for validity of tests for differences in patterns of treatment effects across time, particularly when maximum likelihood procedures are relied upon. Results can be affected significantly by the error specification that is selected, so a principled basis for selecting the specification is important. As no theoretical grounds are usually available to guide this decision, empirical criteria have been developed that focus on model fit. The current report proposes alternative empirical criteria that focus on bootstrap estimates of actual type I error and power of tests for treatment effects. Results for model selection before and after the blind is broken are compared. Goodness-of-fit statistics also compare favourably for models fitted to the blinded or unblinded data, although the correspondence to actual type I error and power depends on the particular fit statistic that is considered. Copyright © 2004 Whurr Publishers Ltd. [source] Hierarchical spatial models for predicting pygmy rabbit distribution and relative abundanceJOURNAL OF APPLIED ECOLOGY, Issue 2 2010Tammy L. Wilson Summary 1.,Conservationists routinely use species distribution models to plan conservation, restoration and development actions, while ecologists use them to infer process from pattern. These models tend to work well for common or easily observable species, but are of limited utility for rare and cryptic species. This may be because honest accounting of known observation bias and spatial autocorrelation are rarely included, thereby limiting statistical inference of resulting distribution maps. 2.,We specified and implemented a spatially explicit Bayesian hierarchical model for a cryptic mammal species (pygmy rabbit Brachylagus idahoensis). Our approach used two levels of indirect sign that are naturally hierarchical (burrows and faecal pellets) to build a model that allows for inference on regression coefficients as well as spatially explicit model parameters. We also produced maps of rabbit distribution (occupied burrows) and relative abundance (number of burrows expected to be occupied by pygmy rabbits). The model demonstrated statistically rigorous spatial prediction by including spatial autocorrelation and measurement uncertainty. 3.,We demonstrated flexibility of our modelling framework by depicting probabilistic distribution predictions using different assumptions of pygmy rabbit habitat requirements. 4.,Spatial representations of the variance of posterior predictive distributions were obtained to evaluate heterogeneity in model fit across the spatial domain. Leave-one-out cross-validation was conducted to evaluate the overall model fit. 5.,Synthesis and applications. Our method draws on the strengths of previous work, thereby bridging and extending two active areas of ecological research: species distribution models and multi-state occupancy modelling. Our framework can be extended to encompass both larger extents and other species for which direct estimation of abundance is difficult. [source] Gender Differences in a Comparison of Two Tested Etiological Models of Cigarette Smoking Among Elementary School Students,JOURNAL OF APPLIED SOCIAL PSYCHOLOGY, Issue 8 2007Randall C. Swaim The theory of reasoned action (TRA), theory of planned behavior (TPB), and a revised TPB were evaluated using manifest variable structural equation modeling among 4th - through 6th -grade students for effectiveness in predicting lifetime cigarette use. TRA was an adequate model for female students, but not male students. TPB resulted in improved model fit over TRA for both male and female students, and a revised TPB model improved fit marginally among female students. Tests for differences across gender indicated that the relationship between intention to use and lifetime cigarette use was stronger among female compared to male students. The results indicate that the TPB is an effective model for predicting lifetime cigarette use among late elementary-school-aged children. [source] Putting density dependence in perspective: nest density, nesting phenology, and biome, all matter to survival of simulated mallard Anas platyrhynchos nestsJOURNAL OF AVIAN BIOLOGY, Issue 3 2009Johan Elmberg Breeding success in ground-nesting birds is primarily determined by nest survival, which may be density-dependent, but the generality of this pattern remains untested. In a replicated crossover experiment conducted on 30 wetlands, survival of simulated mallard nests was related to "biome" (n=14 mediterranean and 16 boreal wetlands), breeding "phenology" (early vs late nests), and "density" (2 vs 8 nests per 225 m shoreline). Local abundances of "waterfowl", "other waterbirds", and "avian predators" were used as covariates. We used an information-theoretic approach and Program MARK to select among competing models. Nest survival was lower in late nests compared with early ones, and it was lower in the mediterranean than in the boreal study region. High-density treatment nests suffered higher depredation rates than low-density nests during days 1,4 of each experimental period. Nest survival was negatively associated with local abundance of "waterfowl" in the boreal but not in the mediterranean biome. Effect estimates from the highest-ranked model showed that nest "density" (d 1,4) had the strongest impact on model fit; i.e. three times that of "biome" and 1.5 times that of "phenology". The latter,s effect, in turn, was twice that of "biome". We argue that our study supports the idea that density-dependent nest predation may be temporally and spatially widespread in waterfowl. We also see an urgent need for research of how waterfowl nesting phenology is matched to that of prey and vegetation. [source] Are niche-based species distribution models transferable in space?JOURNAL OF BIOGEOGRAPHY, Issue 10 2006Christophe F. Randin Abstract Aim, To assess the geographical transferability of niche-based species distribution models fitted with two modelling techniques. Location, Two distinct geographical study areas in Switzerland and Austria, in the subalpine and alpine belts. Methods, Generalized linear and generalized additive models (GLM and GAM) with a binomial probability distribution and a logit link were fitted for 54 plant species, based on topoclimatic predictor variables. These models were then evaluated quantitatively and used for spatially explicit predictions within (internal evaluation and prediction) and between (external evaluation and prediction) the two regions. Comparisons of evaluations and spatial predictions between regions and models were conducted in order to test if species and methods meet the criteria of full transferability. By full transferability, we mean that: (1) the internal evaluation of models fitted in region A and B must be similar; (2) a model fitted in region A must at least retain a comparable external evaluation when projected into region B, and vice-versa; and (3) internal and external spatial predictions have to match within both regions. Results, The measures of model fit are, on average, 24% higher for GAMs than for GLMs in both regions. However, the differences between internal and external evaluations (AUC coefficient) are also higher for GAMs than for GLMs (a difference of 30% for models fitted in Switzerland and 54% for models fitted in Austria). Transferability, as measured with the AUC evaluation, fails for 68% of the species in Switzerland and 55% in Austria for GLMs (respectively for 67% and 53% of the species for GAMs). For both GAMs and GLMs, the agreement between internal and external predictions is rather weak on average (Kulczynski's coefficient in the range 0.3,0.4), but varies widely among individual species. The dominant pattern is an asymmetrical transferability between the two study regions (a mean decrease of 20% for the AUC coefficient when the models are transferred from Switzerland and 13% when they are transferred from Austria). Main conclusions, The large inter-specific variability observed among the 54 study species underlines the need to consider more than a few species to test properly the transferability of species distribution models. The pronounced asymmetry in transferability between the two study regions may be due to peculiarities of these regions, such as differences in the ranges of environmental predictors or the varied impact of land-use history, or to species-specific reasons like differential phenotypic plasticity, existence of ecotypes or varied dependence on biotic interactions that are not properly incorporated into niche-based models. The lower variation between internal and external evaluation of GLMs compared to GAMs further suggests that overfitting may reduce transferability. Overall, a limited geographical transferability calls for caution when projecting niche-based models for assessing the fate of species in future environments. [source] A test of the metapopulation model of the species,area relationshipJOURNAL OF BIOGEOGRAPHY, Issue 8 2002Stephen F. Matter Abstract Aim The species,area relationship is a ubiquitous pattern. Previous methods describing the relationship have done little to elucidate mechanisms producing the pattern. Hanski & Gyllenberg (Science, 1997, 275, 397) have shown that a model of metapopulation dynamics yields predictable species,area relationships. We elaborate on the biological interpretation of this mechanistic model and test the prediction that communities of species with a higher risk of extinction caused by environmental stochasticity should have lower species,area slopes than communities experiencing less impact of environmental stochasticity. Methods We develop the mainland,island version of the metapopulation model and show that the slope of the species,area relationship resulting from this model is related to the ratio of population growth rate to variability in population growth of individual species. We fit the metapopulation model to five data sets, and compared the fit with the power function model and Williams's (Ecology, 1995, 76, 2607) extreme value function model. To test that communities consisting of species with a high risk of extinction should have lower slopes, we used the observation that small-bodied species of vertebrates are more susceptible to environmental stochasticity than large-bodied species. The data sets were divided into small and large bodied species and the model fit to both. Results and main conclusions The metapopulation model showed a good fit for all five data sets, and was comparable with the fits of the extreme value function and power function models. The slope of the metapopulation model of the species,area relationship was greater for larger than for smaller-bodied species for each of five data sets. The slope of the metapopulation model of the species,area relationship has a clear biological interpretation, and allows for interpretation that is rooted in ecology, rather than ad hoc explanation. [source] Development of a measure of sense of community for individuals with serious mental illness residing in community settingsJOURNAL OF COMMUNITY PSYCHOLOGY, Issue 3 2009Greg Townley The psychological sense of community is one of the most commonly investigated constructs in community psychology. Sense of community may be particularly important for individuals with serious mental illness (SMI) because they often face societal barriers to participation in community living, including stigma and discrimination. To date, no published studies have investigated the psychometric qualities of sense of community measures among individuals with SMI. The current study tested a series of confirmatory factor analyses using the Brief Sense of Community Index (Long & Perkins, 2003) in a sample of 416 persons with SMI living in community settings to suggest a model of sense of community for individuals with SMI and other disabilities. The resulting scale, the Brief Sense of Community Index-Disability, demonstrated good model fit and construct validity. Implications are discussed for how this scale may be used in research investigating community integration and adaptive functioning in community settings. © 2009 Wiley Periodicals, Inc. [source] A Comparison of Item Fit Statistics for Mixed IRT ModelsJOURNAL OF EDUCATIONAL MEASUREMENT, Issue 3 2010Kyong Hee Chon In this study we examined procedures for assessing model-data fit of item response theory (IRT) models for mixed format data. The model fit indices used in this study include PARSCALE's,G2,,Orlando and Thissen's,S,,,X2,and,S,,,G2,,and Stone's,,2*,and,G2*. To investigate the relative performance of the fit statistics at the item level, we conducted two simulation studies: Type I error and power studies. We evaluated the performance of the item fit indices for various conditions of test length, sample size, and IRT models. Among the competing measures, the summed score-based indices,S,,,X2,and,S,,,G2,were found to be the sensible and efficient choice for assessing model fit for mixed format data. These indices performed well, particularly with short tests. The pseudo-observed score indices, ,2*,and,G2*,,showed inflated Type I error rates in some simulation conditions. Consistent with the findings of current literature, the PARSCALE's,G2,index was rarely useful, although it provided reasonable results for long tests. [source] Comparing the Difficulty of Examination Subjects with Item Response TheoryJOURNAL OF EDUCATIONAL MEASUREMENT, Issue 2 2008Oksana B. Korobko Methods are presented for comparing grades obtained in a situation where students can choose between different subjects. It must be expected that the comparison between the grades is complicated by the interaction between the students' pattern and level of proficiency on one hand, and the choice of the subjects on the other hand. Three methods based on item response theory (IRT) for the estimation of proficiency measures that are comparable over students and subjects are discussed: a method based on a model with a unidimensional representation of proficiency, a method based on a model with a multidimensional representation of proficiency, and a method based on a multidimensional representation of proficiency where the stochastic nature of the choice of examination subjects is explicitly modeled. The methods are compared using the data from the Central Examinations in Secondary Education in the Netherlands. The results show that the unidimensional IRT model produces unrealistic results, which do not appear when using the two multidimensional IRT models. Further, it is shown that both the multidimensional models produce acceptable model fit. However, the model that explicitly takes the choice process into account produces the best model fit. [source] An Application of Item Response Time: The Effort-Moderated IRT ModelJOURNAL OF EDUCATIONAL MEASUREMENT, Issue 1 2006Steven L. Wise The validity of inferences based on achievement test scores is dependent on the amount of effort that examinees put forth while taking the test. With low-stakes tests, for which this problem is particularly prevalent, there is a consequent need for psychometric models that can take into account differing levels of examinee effort. This article introduces the effort-moderated IRT model, which incorporates item response time into proficiency estimation and item parameter estimation. In two studies of the effort-moderated model when rapid guessing (i.e., reflecting low examinee effort) was present, one based on real data and the other on simulated data, the effort-moderated model performed better than the standard 3PL model. Specifically, it was found that the effort-moderated model (a) showed better model fit, (b) yielded more accurate item parameter estimates, (c) more accurately estimated test information, and (d) yielded proficiency estimates with higher convergent validity. [source] Pre-school children with and without developmental delay: behaviour problems and parenting stress over timeJOURNAL OF INTELLECTUAL DISABILITY RESEARCH, Issue 4-5 2003B. L. Baker Abstract Background Children with intellectual disability are at heightened risk for behaviour problems and diagnosed mental disorder. Methods The present authors studied the early manifestation and continuity of problem behaviours in 205 pre-school children with and without developmental delays. Results Behaviour problems were quite stable over the year from age 36,48 months. Children with developmental delays were rated higher on behaviour problems than their non-delayed peers, and were three times as likely to score in the clinical range. Mothers and fathers showed high agreement in their rating of child problems, especially in the delayed group. Parenting stress was also higher in the delayed group, but was related to the extent of behaviour problems rather than to the child's developmental delay. Conclusions Over time, a transactional model fit the relationship between parenting stress and behaviour problems: high parenting stress contributed to a worsening in child behaviour problems over time, and high child behaviour problems contributed to a worsening in parenting stress. Findings for mothers and fathers were quite similar. [source] A disaggregated empirical analysis of the determinants of IMF arrangements: Does one model fit all?JOURNAL OF INTERNATIONAL DEVELOPMENT, Issue 7 2009Graham Bird JEL: F33, F3 Abstract Does one model fit all when it comes to the determinants of IMF programs? Certainly claims have been made by the IMF that capital account crisis (CAC) countries are discernibly different in terms of the characteristics that lead them to borrow from it, while other research has claimed that it is only Asian economies that are different from the rest. This paper sets out to examine these issues. It tests various forms of a fairly conventional model to see whether some forms better fit certain groups of countries than others. It then uses the favoured models to estimate the probability of countries having an IMF arrangement. In particular it examines countries that have been identified by the Fund as CAC countries, but it also looks at a number of comparator countries. The findings suggest that there are some differences between low income and middle income countries. Pressures in the foreign exchange market are significant for the latter but not for the former. The paper also discusses differences between regions and within regions. Broadly speaking the findings confirm that Asian economies around the time of the 1997/1998 crisis tended to turn to the IMF for financial support more quickly than would have been anticipated on the basis of the existing best-fitting models. The paper also discusses the implications of the findings for policy and for the reform of the IMF. Copyright © 2008 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||