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Equation Models (equation + models)
Kinds of Equation Models Selected AbstractsComparing Structural Equation Models That Use Different Measures of the Level of Response to AlcoholALCOHOLISM, Issue 5 2010Marc A. Schuckit Background:, The two measures of a low level of response (LR) to alcohol, an alcohol challenge and the retrospective Self-Report of the Effects of Alcohol questionnaire (SRE), each identify individuals at high risk for heavy drinking and alcohol problems. These measures also perform similarly in identifying subjects with unique functional brain imaging characteristics. However, few data are available regarding whether alcohol challenge-based and SRE-based LRs operate similarly in structural equation models (SEMs) that search for characteristics, which help to mediate how LR impacts alcohol outcomes. Methods:, Two hundred and ninety-four men from the San Diego Prospective Study were evaluated for their LR to alcohol using alcohol challenges at ,age 20. At ,age 35, the same subjects filled out the SRE regarding the number of drinks needed for effects 15 to 20 years earlier. The two different LR scores for these men were used in SEM analyses evaluating how LR relates to future heavy drinking and to drinking in peers (PEER), alcohol expectancies (EXPECT), and drinking to cope (COPE) as potential mediators of the LR to drinking pattern (ALCOUT) relationships. Results:, While the 2 LR measures that were determined 15 years apart related to each other at a modest level (r = 0.17, p < 0.01), the SEM results were similar regardless of the LR source. In both alcohol challenge-based and SRE-based LR models, LR related directly to ALCOUT, with partial mediation from PEER and COPE, but not through EXPECT in these 35-year-old men. Conclusions:, Consistent with the >60% overlap in prediction of outcomes for the 2 LR measures, and with results from functional brain imaging, alcohol challenge- and SRE-based LR values operated similarly in SEM models in these men. [source] Residual-Based Diagnostics for Structural Equation ModelsBIOMETRICS, Issue 1 2009B. N. Sánchez Summary Classical diagnostics for structural equation models are based on aggregate forms of the data and are ill suited for checking distributional or linearity assumptions. We extend recently developed goodness-of-fit tests for correlated data based on subject-specific residuals to structural equation models with latent variables. The proposed tests lend themselves to graphical displays and are designed to detect misspecified distributional or linearity assumptions. To complement graphical displays, test statistics are defined; the null distributions of the test statistics are approximated using computationally efficient simulation techniques. The properties of the proposed tests are examined via simulation studies. We illustrate the methods using data from a study of in utero lead exposure. [source] Master Equation Models for the Pressure- and Temperature-Dependent Reactions HO + NO2 , HONO2 and HO + NO2 , HOONOCHEMINFORM, Issue 7 2004David M. Golden Abstract For Abstract see ChemInform Abstract in Full Text. [source] Factorial Invariance Within Longitudinal Structural Equation Models: Measuring the Same Construct Across TimeCHILD DEVELOPMENT PERSPECTIVES, Issue 1 2010Keith F. Widaman Abstract, Charting change in behavior as a function of age and investigating longitudinal relations among constructs are primary goals of developmental research. Traditionally, researchers rely on a single measure (e.g., scale score) for a given construct for each person at each occasion of measurement, assuming that measure reflects the same construct at each occasion. With multiple indicators of a latent construct at each time of measurement, the researcher can evaluate whether factorial invariance holds. If factorial invariance constraints are satisfied, latent variable scores at each time of measurement are on the same metric and stronger conclusions are warranted. This article discusses factorial invariance in longitudinal studies, contrasting analytic approaches and highlighting strengths of the multiple-indicator approach to modeling developmental processes. [source] Daily computer usage correlated with undergraduate students' musculoskeletal symptoms,AMERICAN JOURNAL OF INDUSTRIAL MEDICINE, Issue 6 2007Che-hsu (Joe) Chang PT Abstract Background A pilot prospective study was performed to examine the relationships between daily computer usage time and musculoskeletal symptoms on undergraduate students. Methods For three separate 1-week study periods distributed over a semester, 27 students reported body part-specific musculoskeletal symptoms three to five times daily. Daily computer usage time for the 24-hr period preceding each symptom report was calculated from computer input device activities measured directly by software loaded on each participant's primary computer. General Estimating Equation models tested the relationships between daily computer usage and symptom reporting. Results Daily computer usage longer than 3 hr was significantly associated with an odds ratio 1.50 (1.01,2.25) of reporting symptoms. Odds of reporting symptoms also increased with quartiles of daily exposure. Conclusions These data suggest a potential dose,response relationship between daily computer usage time and musculoskeletal symptoms. Am. J. Ind. Med. 50:481,488, 2007. © 2007 Wiley-Liss, Inc. [source] Effect of maternal asthma on the risk of specific congenital malformations: A population-based cohort study,,§BIRTH DEFECTS RESEARCH, Issue 4 2010Lucie Blais Abstract BACKGROUND There is a lack of consensus in the literature about the effect of maternal asthma on the development of congenital malformations. OBJECTIVE To further examine the association between maternal asthma and the risk of congenital malformations. METHODS A cohort of 41,637 pregnancies from women with and without asthma who delivered between 1990 and 2002 was reconstructed by linking three Quebec (Canada) administrative databases. All cases of malformations were identified using either the medical services or the hospital databases. The main exposure was maternal asthma, defined by the presence of at least one asthma diagnosis and at least one prescription for an asthma medication at any time in the two years before or during pregnancy. Generalized Estimation Equation models were performed to estimate the adjusted odds ratio (OR) of congenital malformations as a function of maternal asthma. RESULTS The crude prevalences of any congenital malformation were 9.5% and 7.5% for women with and without asthma, respectively. Maternal asthma was significantly associated with an increased risk of any malformation (OR=1.30; 95% CI: 1.20-1.40) and three specific groups (at the 0.0028 level): nervous system (excluding spina bifida: OR=1.83; 1.37-2.83); respiratory system (OR=1.75; 1.21-2.53); and digestive system (OR=1.48; 1.19-1.85). CONCLUSIONS Maternal asthma increases the risk of specific groups of congenital malformations. The disease itself, through fetal oxygen impairment, is likely to play a role in this increased risk, but more research is needed to disentangle the relative effect of asthma and medications used to treat this disease. Birth Defects Research (Part A), 2010. © 2010 Wiley-Liss, Inc. [source] Identification in Nonparametric Simultaneous Equations ModelsECONOMETRICA, Issue 5 2008Rosa L. Matzkin This paper provides conditions for identification of functionals in nonparametric simultaneous equations models with nonadditive unobservable random terms. The conditions are derived from a characterization of observational equivalence between models. We show that, in the models considered, observational equivalence can be characterized by a restriction on the rank of a matrix. The use of the new results is exemplified by deriving previously known results about identification in parametric and nonparametric models as well as new results. A stylized method for analyzing identification, which is useful in some situations, is also presented. [source] Intergenerational linkages in antisocial behaviourCRIMINAL BEHAVIOUR AND MENTAL HEALTH, Issue 2 2009Terence P. Thornberry Background,A life-course perspective was used to examine whether a parent's adolescent antisocial behaviour increases the chances of his or her child being involved in antisocial behaviour and, if so, the extent to which different aspects of parenting mediate this relationship. Aim,It was hypothesised that there will be significant levels of intergenerational continuity in antisocial behaviour when parents have ongoing contact with the child, and that stress from parenting and ineffective parenting styles will mediate this relationship. Method,Longitudinal data from the Rochester Intergenerational Study were used to test these issues in structural equation models for fathers and for mothers. Results,Parental antisocial behaviour is significantly related to child antisocial behaviour for mothers and for fathers who have frequent contact with the child, but not for fathers with infrequent contact. For mothers, the impact of adolescent antisocial behaviour on the child's antisocial behaviour is primarily mediated through parenting stress and effective parenting. For high-contact fathers there are multiple mediating pathways that help explain the impact of their adolescent antisocial behaviour on their child's behaviour. Conclusions,The roots of antisocial behaviour extend back at least to the parent's adolescence, and parenting interventions need to consider these long-term processes. Copyright © 2009 John Wiley & Sons, Ltd. [source] Depression and obesity: do shared genes explain the relationship?DEPRESSION AND ANXIETY, Issue 9 2010Niloofar Afari Ph.D. Abstract Background: Studies have found a modest association between depression and obesity, especially in women. Given the substantial genetic contribution to both depression and obesity, we sought to determine whether shared genetic influences are responsible for the association between these two conditions. Methods: Data were obtained from 712 monozygotic and 281 dizygotic female twin pairs who are members of the community-based University of Washington Twin Registry. The presence of depression was determined by self-report of doctor-diagnosed depression. Obesity was defined as body mass index of ,30,kg/m2, based on self-reported height and weight. Generalized estimating regression models were used to assess the age-adjusted association between depression and obesity. Univariate and bivariate structural equation models estimated the components of variance attributable to genetic and environmental influences. Results: We found a modest phenotypic association between depression and obesity (odds ratio=1.6, 95% confidence interval=1.2,2.1). Additive genetic effects contributed substantially to depression (57%) and obesity (81%). The best-fitting bivariate model indicated that 12% of the genetic component of depression is shared with obesity. Conclusions: The association between depression and obesity in women may be in part due to shared genetic risk for both conditions. Future studies should examine the genetic, environmental, social, and cultural mechanisms underlying the relationship between this association. Depression and Anxiety, 2010. © 2010 Wiley-Liss, Inc. [source] Outcomes for 236 patients from a 2-year early intervention in psychosis serviceACTA PSYCHIATRICA SCANDINAVICA, Issue 2 2009M. A. Turner Objective:, To examine: i) changes in key outcome measures over time in treatment in a representative first-episode psychosis treatment cohort and ii) baseline predictors of service disengagement. Method:, Baseline characteristics of 236 patients were examined for associations with outcomes over time using generalized estimating equation models. The data on disengagement were analysed using logistic regression. Results:, After controlling for admission scores, patients showed consistently improved outcomes while in treatment on functional recovery (unemployment, P < 0.01; HoNOS, P < 0.001; the Quality of Life Scale, P < 0.001; GAF, P < 0.05) but not symptomatology (as assessed by the PANSS and substance abuse). The 64 (33%) who disengaged were more likely to be unemployed (P < 0.01) and have higher HoNOS (P < 0.01) and GAF (P < 0.05) scores at baseline. Conclusion:, This evaluation has shown significant improvements in psychosocial functioning but not psychopathology during treatment at an Early Intervention for Psychosis Service. Despite attempts to retain patients, there is a high rate of treatment discontinuation. [source] Seismic interaction in electrical substation equipment connected by non-linear rigid bus conductorsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2007Junho Song Abstract An important element within the power transmission lifeline is the electrical substation that typically consists of a complex set of equipment items interconnected through conductor buses or cables. If the connections are not sufficiently flexible, significant dynamic interaction may occur between the connected equipment items during a seismic event, which may result in damage and loss of the equipment. This paper investigates the interaction effect between electrical substation equipment items connected by non-linear rigid bus conductors. The equipment items are modelled as single-degree-of-freedom oscillators by use of appropriate shape functions. The hysteretic behaviours of rigid bus connectors are described by differential equation models fitted to experimental data. An efficient non-linear random vibration method is used to quantify the seismic interaction effect of the connected equipment items. Based on the developed analytical models and method, the effect of interaction in the connected equipment system is investigated through extensive parametric studies. The results lead to practical charts and guidelines for the seismic design of interconnected electrical substation equipment. Copyright © 2006 John Wiley & Sons, Ltd. [source] Statistical methods for the evaluation of health effects of prenatal mercury exposureENVIRONMETRICS, Issue 2 2003Esben Budtz-Jřrgensen Abstract Environmental risk assessment based on epidemiological data puts stringent demands on the statistical procedures. First, convincing evidence has to be established that there is a risk at all. In practice this endeavor requires prudent use of the observational epidemiological information with delicate balancing between utilizing the information optimally but not over-interpreting it. If a case for an environmental risk has been made, the second challenge is to provide useful input that regulatory authorities can use to set standards. This article surveys some of these issues in the concrete case of neurobehavioral effects in Faroese children prenatally exposed to methylmercury. A selection of modern, appropriate methods has been applied in the analysis of this material that may be considered typical of environmental epidemiology today. In particular we emphasize the potential of structural equation models for improving standard multiple regression analysis of complex environmental epidemiology data. Copyright © 2003 John Wiley & Sons, Ltd. [source] Twenty-five strategies for improving the design, implementation and analysis of health services research related to alcohol and other drug abuse treatmentADDICTION, Issue 11s3 2000Michael L. Dennis While some aspects of addiction can be studied in laboratory or controlled settings, the study of long-term recovery management and the health services that support it requires going out into the community and dealing with populations and systems that are much more diverse and less under our control. This in turn raises many methodological challenges for the health service researchers studying alcohol and other drug abuse treatment. This paper identifies some of these challenges related to the design, measurement, implementation and effectiveness of health services research. It then recommends 25 strategies (and key primers) for addressing them: (1) identifying in advance all stakeholders and issues; (2) developing conceptual models of intervention and context; (3) identifying the population to whom the conclusions will be generalized; (4) matching the research design to the question; (5) conducting randomized experiments only when appropriate and necessary; (6) balancing methodological and treatment concerns; (7) prioritizing analysis plans and increasing design sensitivity, (8) combining qualitative and quantitative methods; (9) identifying the four basic types of measures needed; (10) identifying and using standardized measures; (11) carefully balancing measurement selection and modification; (12) developing and evaluating modified and new measures when necessary; (13) identifying and tracking major clinical subgroups; (14) measuring and analyzing the actual pattern of services received; (15) incorporating implementation checks into the design; (16) inc rporating baseline measures into the intervention; (17) monitoring implementation and dosage as a form of quality assurance; (18) developing procedures early to facilitate tracking and follow-up of study participants; (19) using more appropriate representations of the actual experiment; (20) using appropriate and sensitive standard deviation terms; (21) partialing out variance due to design or known sources prior to estimating experimental effect sizes; (22) using dimensional, interval and ratio measures to increase sensitivity to change; (23) using path or structural equation models; (24) integrating qualitative and quantitative analysis into reporting; and (25) using quasi-experiments, economic or organizational studies to answer other likely policy questions. Most of these strategies have been tried and tested in this and other areas, but are not widely used. Improving the state of the art of health services research and bridging the gap between research and practice do not depend upon using the most advanced methods, but rather upon using the most appropriate methods. [source] Cessation of periodontal care during pregnancy: effect on infant birthweightEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 1 2006Philippe P. Hujoel The goal of this study was to assess whether interruption of care for chronic periodontitis during pregnancy increased the risk of low-birthweight infants. A population-based case-control study was designed with 793 cases (infants <,2,500 g) and a random sample of 3,172 controls (infants ,,2,500 g). Generalized estimating equation models were used to relate periodontal treatment history to low birthweight risk and to common risk factors. The results indicate that periodontal care utilization was associated with a 2.35-fold increased odds of self-reported smoking during pregnancy (95% confidence interval: 1.48,3.71), a 2.19-fold increased odds for diabetes (95% confidence interval: 1.21,3.98), a 3.90-fold increased odds for black race (95% confidence interval: 2.31,6.61), and higher maternal age. After adjustment for these factors, interruption of periodontal care during pregnancy did not lead to an increased risk for a low-birthweight infant when compared to women with no history of periodontal care (odds ratio, 0.96; 95% confidence interval, 0.60,1.52). In conclusion, women receiving periodontal care had genetic and environmental characteristics, such as smoking, diabetes and race, that were associated with an increased risk for low-birthweight infants. Periodontal care patterns, in and of themselves, were unrelated to low-birthweight risk. [source] A stronger latent-variable methodology to actual,ideal discrepancyEUROPEAN JOURNAL OF PERSONALITY, Issue 7 2008L. Francesca Scalas Abstract We introduce a latent actual,ideal discrepancy (LAID) approach based on structural equation models (SEMs) with multiple indicators and empirically weighted variables. In Study 1, we demonstrate with simulated data, the superiority of a weighted approach to discrepancy in comparison to a classic unweighted one. In Study 2, we evaluate the effects of actual and ideal appearance on physical self-concept and self-esteem. Actual appearance contributes positively to physical self-concept and self-esteem, whereas ideal appearance contributes negatively. In support of multidimensional perspective, actual - and ideal -appearance effects on self-esteem are substantially,but not completely,mediated by physical self-concept. Whereas this pattern of results generalises across gender and age, multiple-group invariance tests show that the effect of actual appearance on physical self-concept is larger for women than for men. Copyright © 2008 John Wiley & Sons, Ltd. [source] A Structural Equation Approach to Models with Spatial DependenceGEOGRAPHICAL ANALYSIS, Issue 2 2008Johan H. L. Oud We introduce the class of structural equation models (SEMs) and corresponding estimation procedures into a spatial dependence framework. SEM allows both latent and observed variables within one and the same (causal) model. Compared with models with observed variables only, this feature makes it possible to obtain a closer correspondence between theory and empirics, to explicitly account for measurement errors, and to reduce multicollinearity. We extend the standard SEM maximum likelihood estimator to allow for spatial dependence and propose easily accessible SEM software like LISREL 8 and Mx. We present an illustration based on Anselin's Columbus, OH, crime data set. Furthermore, we combine the spatial lag model with the latent multiple-indicators,multiple-causes model and discuss estimation of this latent spatial lag model. We present an illustration based on the Anselin crime data set again. [source] Examining Adolescents' Responses to Antimarijuana PSAsHUMAN COMMUNICATION RESEARCH, Issue 3 2003Michael T. Stephenson The research reported here investigated sensation seeking as a moderating variable of 368 adolescents' reactions to antimarijuana public service announcements. Participants rated the perceived message sensation value of 3 antimarijuana TV ads, their processing of the consequences of marijuana use, their affective responses to the ads, and antimarijuana attitudes. Two structural equation models,1 for high sensation seekers and the other for low sensation seekers,revealed 2 very different styles of processing the ads. Specifically, antimarijuana attitudes for high sensation seekers were influenced directly and indirectly by sympathetic distress and directly by argument-based processing. In contrast, antimarijuana attitudes for low sensation seekers were influenced solely by argument-based processing. [source] A 2D implicit time-marching algorithm for shallow water models based on the generalized wave continuity equationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2004Kendra M. Dresback Abstract This paper builds upon earlier work that developed and evaluated a 1D predictor,corrector time-marching algorithm for wave equation models and extends it to 2D. Typically, the generalized wave continuity equation (GWCE) utilizes a three time-level semi-implicit scheme centred at k, and the momentum equation uses a two time-level scheme centred at k+12. It has been shown that in highly non-linear applications, the algorithm becomes unstable at even moderate Courant numbers. This work implements and analyses an implicit treatment of the non-linear terms through the use of an iterative time-marching algorithm in the two-dimensional framework. Stability results show at least an eight-fold increase in the maximum time step, depending on the domain. Studies also examined the sensitivity of the G parameter (a numerical weighting parameter in the GWCE) with results showing the greatest increase in stability occurs when 1,G/,max,10, a range that coincides with the recommended range to minimize errors. Convergence studies indicate an increase in temporal accuracy from first order to second order, while overall error is less than the original algorithm, even at higher time steps. Finally, a parallel implementation of the new algorithm shows that it scales well. Copyright © 2004 John Wiley & Sons, Ltd. [source] URANS computations for an oscillatory non-isothermal triple-jet using the k,, and second moment closure turbulence modelsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2003M. Nishimura Abstract Low Reynolds number turbulence stress and heat flux equation models (LRSFM) have been developed to enhance predictive capabilities. A new method is proposed for providing the wall boundary condition for dissipation rate of turbulent kinetic energy, ,, to improve the model capability upon application of coarse meshes for practical use. The proposed method shows good agreement with accepted correlations and experimental data for flows with various Reynolds and Prandtl numbers including transitional regimes. Also, a mesh width about 5 times or larger than that used in existing models is applicable by using the present boundary condition. The present method thus enhanced computational efficiency in applying the complex turbulence model, LRSFM, to predictions of complicated flows. Unsteady Reynolds averaged Navier,Stokes (URANS) computations are conducted for an oscillatory non-isothermal quasi-planar triple-jet. Comparisons are made between an experiment and predictions with the LRSFM and the standard k,, model. A water test facility with three vertical jets, the cold in between two hot jets, simulates temperature fluctuations anticipated at the outlet of a liquid metal fast reactor core. The LRSFM shows good agreement with the experiment, with respect to mean profiles and the oscillatory motion of the flow, while the k,, model under-predicts the mixing due to the oscillation, such that a transverse mean temperature difference remains far downstream. Copyright © 2003 John Wiley & Sons, Ltd. [source] Measuring customer value and satisfaction in services transactions, scale development, validation and cross-cultural comparisonINTERNATIONAL JOURNAL OF CONSUMER STUDIES, Issue 6 2007Frank Huber Abstract Customer value and customer satisfaction are pivotal but at the same time elusive concepts in services marketing theory. This paper focuses on discussing the relationship between these two concepts. We propose operationalization by developing and testing scales, especially operational indicators, for important dimensions and drivers of the services-value construct. A multitrait-multimethod design is used to test the robustness of the operationalization. Furthermore, a cross-cultural data set is used to explore country influences using confirmatory factor analysis and structural equation models. Results indicate that the measurement construct is robust and useful in country-comparative studies. [source] Provider Characteristics Related to Antidepressant Use in Older PeopleJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 6 2006Gerda G. Fillenbaum PhD OBJECTIVES: To determine whether the characteristics of the usual medical care providers of older antidepressant users changed between 1986 and 1997 with the introduction of selective serotonin reuptake inhibitors. DESIGN: Longitudinal study. SETTING: Five-county Piedmont area of North Carolina. PARTICIPANTS: Stratified random sample of African-American (n=2,261) and white (n=1,875) community residents aged 65 to 105. MEASUREMENTS: Sample members provided information on prescription medications, demographic and health status, and usual medical care provider (matched to North Carolina Health Professions Data Systems files to ascertain provider characteristics) in 1986/87, 1989/90, 1992/93, and 1996/97. Most (77.5%) named a provider (name unmatchable for 4.1%). Sample member characteristics were aggregated into probability (propensity) scores summarizing predisposing (demographic), enabling (medical care access), and need (health status) categories. Along with wave of study and whether a provider was named, these were entered as control variables in generalized estimating equation models that examined the association between provider race (white vs nonwhite), sex, age, location of practice, and primary versus specialist care and antidepressant use. RESULTS: The characteristics of the usual medical care providers remained stable over the decade, although prevalence of antidepressant use increased. Two provider characteristics,race and area of practice (but not the interaction between them),were significantly associated with patients' use of antidepressants. Patients of white physicians and of physicians with urban practices were more likely to use antidepressants. CONCLUSION: Although use of antidepressants has increased over time, there has been little change in the characteristics of users' usual medical care providers. [source] Cognitive Status, Muscle Strength, and Subsequent Disability in Older Mexican AmericansJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 9 2005Mukaila A. Raji MD Objectives: To examine the association between Mini-Mental State Examination (MMSE) score and subsequent muscle strength (measured using handgrip strength) and to test the hypothesis that muscle strength will mediate any association between impaired cognition and incident activity of daily living (ADL) disability over a 7-year period in elderly Mexican Americans who were initially not disabled. Design: A 7-year prospective cohort study (1993,2001). Setting: Five southwestern states (Texas, New Mexico, Colorado, Arizona, and California). Participants: Two thousand three hundred eighty-one noninstitutionalized Mexican-American men and women aged 65 and older with no ADL disability at baseline. Measurements: In-home interviews in 1993/1994, 1995/1996, 1998/1999, and 2000/2001 assessed social and demographic factors, medical conditions (diabetes mellitus, stroke, heart attack, and arthritis), body mass index (BMI), depressive symptomatology, handgrip muscle strength, and ADLs. MMSE score was dichotomized as less than 21 for poor cognition and 21 or greater for good cognition. Main outcomes measures were mean and slope of handgrip muscle strength over the 7-year period and incident disability, defined as new onset of any ADL limitation at the 2-, 5-, or 7-year follow-up interview periods. Results: In mixed model analyses, there was a significant cross-sectional association between having poor cognition (MMSE<21) and lower handgrip strength, independent of age, sex, and time of interview (estimate=,1.41, standard error (SE)=0.18; P<.001). With the introduction of a cognition-by-time interaction term into the model, there was also a longitudinal association between poor cognition and change in handgrip strength over time (estimate=,0.25, SE=0.06; P<.001), indicating that subjects with poor cognition had a significantly greater decline in handgrip strength over 7 years than those with good cognition, independent of age, sex, and time. This longitudinal association between poor cognition and greater muscle decline remained significant (P<.001) after controlling for age, sex, education, and time-dependent variables of depression, BMI, and medical conditions. In general estimation equation models, having poor cognition was associated with greater risk of 7-year incident ADL disability (odds ratio=2.01, 95% confidence interval (CI)=1.60,2.52); the magnitude of the association decreased to 1.66 (95% CI=1.31,2.10) when adjustment was made for handgrip strength. Conclusion: Older Mexican Americans with poor cognition had steeper decline in handgrip muscle strength over 7 years than those with good cognition, independent of other demographic and health factors. A possible mediating effect of muscle strength on the association between poor cognition and subsequent ADL disability was also indicated. [source] Social capital, safety concerns, parenting, and early adolescents' antisocial behaviorJOURNAL OF COMMUNITY PSYCHOLOGY, Issue 3 2010Alessio Vieno This study explores the relations between neighborhood social capital (neighbor support and social climate), safety concerns (fear of crime and concern for one's child), parenting (solicitation and support), and adolescent antisocial behavior in a sample of 952 parents (742 mothers) and 588 boys and 559 girls from five middle schools (sixth through eighth grades) in a midsize Italian city. In structural equation models, social capital is strongly and inversely related to safety concerns and positively related to parental support and solicitation. In turn, safety concerns are also positively related to parental support and solicitation. Social capital and safety concerns have indirect effects on children's antisocial behavior through their effects on parenting. Implications are discussed for parenting and community-based interventions to prevent or reduce youth antisocial behaviors. © 2010 Wiley Periodicals, Inc. [source] PHYSICAL, PHYSIOLOGICAL AND CHEMICAL CHANGES IN POTATO AS INFLUENCED BY ERWINIA CAROTOVORA INFECTIONJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 5 2002F. NOURIAN Bacterial soft rot, caused by Erwinia carotovora ssp. carotovora (Ecc), is a major disease in stored potatoes. The pathogen causes different physical, physiological and chemical changes in potatoes, which may affect the acceptability of raw and processed products. This study was carried out to evaluate the effect of disease severity on different physico-chemical and physiological properties of raw and cooked potatoes and to select the parameters most responsive to disease severity. Potatoes were inoculated with bacteria and incubated at 20C for different lengths of time to produce different levels of disease. As incubation time increased the volume of disease (VDS) increased, which in turn influenced the respiration rate (RR). In both raw and cooked potatoes, the physical changes (texture and color) associated with the progress of disease were reduced hardness, firmness and L value, and increased a and b values and total color difference (,E). The chemical changes were reduced ascorbic acid and pH, and increased reducing sugars, total sugars and titrable acidity along with the activities of peroxidase and polyphenol oxidase. The changes in physical and chemical parameters of raw and cooked potatoes during storage were described by fractional conversion equation models. All parameters were quite sensitive to disease except reducing sugars, peroxidase and PPO activity. The correlation matrix indicated that several of the quality parameters were related and thus most of them could be successfully used to predict tuber quality from disease. [source] The Association Between Partner Enhancement and Self-Enhancement and Relationship Quality OutcomesJOURNAL OF MARRIAGE AND FAMILY, Issue 3 2009Dean M. Busby The purpose of this research was to understand in greater detail, using 2 samples (Study 1 N = 4,881 heterosexual couples; Study 2 N = 335 heterosexual couples who completed the Relationship Evaluation Questionnaire), how partner or self-enhancement patterns differentially influence relationship outcomes. A multivariate analysis of covariance was conducted comparing 4 outcome measures for different couple types in which individuals rated the partner higher, the same, or lower than they rated themselves on affability. Couples in which both individuals perceived themselves as more affable than the partner experienced poorer results on the relationship outcome measures, whereas couples in which both individuals perceived the partner's personality as more affable than their own experienced more positive relationship outcomes. Additional analyses with structural equation models demonstrated the consistent influence of enhancement measures on relationship outcomes for cross-sectional and longitudinal samples. [source] A Behavioral Genetic Analysis of the Relationship Between the Socialization Scale and Self-Reported DelinquencyJOURNAL OF PERSONALITY, Issue 1 2000Jeanette Taylor This investigation examined the genetic (A), and shared (C) and nonshared (E) environmental variance contributions to the relationship of self-reported delinquency (as measured by the "Delinquent Behavior Inventory" [DBI; Gibson, 1967]) to the Socialization (So) scale of the California Psychological Inventory using univariate and bivariate structural equation models. The scales were administered to 222 male (145 monozygotic; 77 dizygotic) and 159 female (107 monozygotic; 52 dizygotic) 16- to 18-year-old same-sex twin pairs. Principal components analysis with varimax rotation revealed three interpretable So factors representing family/home environment, self-concept, and behavioral control. Univariate modeling suggested sex differences in etiological influences associated with individual differences in most scales. The bivariate ACE model fit the data, suggesting that the covariance between the So scale and self-reported delinquency owes in part to shared etiological factors. [source] Comparing Structural Equation Models That Use Different Measures of the Level of Response to AlcoholALCOHOLISM, Issue 5 2010Marc A. Schuckit Background:, The two measures of a low level of response (LR) to alcohol, an alcohol challenge and the retrospective Self-Report of the Effects of Alcohol questionnaire (SRE), each identify individuals at high risk for heavy drinking and alcohol problems. These measures also perform similarly in identifying subjects with unique functional brain imaging characteristics. However, few data are available regarding whether alcohol challenge-based and SRE-based LRs operate similarly in structural equation models (SEMs) that search for characteristics, which help to mediate how LR impacts alcohol outcomes. Methods:, Two hundred and ninety-four men from the San Diego Prospective Study were evaluated for their LR to alcohol using alcohol challenges at ,age 20. At ,age 35, the same subjects filled out the SRE regarding the number of drinks needed for effects 15 to 20 years earlier. The two different LR scores for these men were used in SEM analyses evaluating how LR relates to future heavy drinking and to drinking in peers (PEER), alcohol expectancies (EXPECT), and drinking to cope (COPE) as potential mediators of the LR to drinking pattern (ALCOUT) relationships. Results:, While the 2 LR measures that were determined 15 years apart related to each other at a modest level (r = 0.17, p < 0.01), the SEM results were similar regardless of the LR source. In both alcohol challenge-based and SRE-based LR models, LR related directly to ALCOUT, with partial mediation from PEER and COPE, but not through EXPECT in these 35-year-old men. Conclusions:, Consistent with the >60% overlap in prediction of outcomes for the 2 LR measures, and with results from functional brain imaging, alcohol challenge- and SRE-based LR values operated similarly in SEM models in these men. [source] A STRUCTURAL EQUATION MODELING OF ALCOHOL USE AMONG YOUNG ADULTS IN THE U.S. MILITARY: COMPLEXITIES AMONG STRESS, DRINKING MOTIVES, IMPULSIVITIY, ALCOHOL USE AND JOB PERFORMANCEALCOHOLISM, Issue 2008Sunju Sohn Aims:, Young male adults in the U. S. military drink at much higher rates than civilians and females of the same age. Drinking has been shown to be associated with stress and individuals' ability to effectively cope with stressors. Despite numerous studies conducted on young adults' drinking behaviors such as college drinking, current literature is limited in fully understanding alcohol use patterns of the young military population. The aim of the present study was to develop and test the hypothesized Structural Equation Model (SEM) of alcohol use to determine if stress coping styles moderate the relationship between stress, drinking motives, impulsivity, alcohol consumption and job performance. Methods:, Structural equation models for multiple group comparisons were estimated based on a sample of 1,715 young (aged 18 to 25) male military personnel using the 2005 Department of Defense Survey of Health Related Behaviors among Military Personnel. Coping style was used as the grouping factor in the multi-group analysis and this variable was developed through numerous steps to reflect positive and negative behaviors of coping. The equivalences of the structural relations between the study variables were then compared across two groups at a time, controlling for installation region, race/ethnicity, marital status, education, and pay grade, resulting in two model comparisons with four coping groups. If the structural weight showed differences across groups, each parameter was constrained and tested one at a time to see where the models are different. Results:, The results showed that the hypothesized model applies across all groups. The structural weights revealed that a moderation effect exists between a group whose tendency is to mostly use positive coping strategies and a group whose tendency is to mostly use negative coping strategies (,,2(39)= 65.116, p<.05). More specifically, the models were different (with and without Bonferroni Type I error correction) in the paths between "motive and alcohol use" and "alcohol use and alcohol-related consequences (job performance)." Conclusions:, It seems plausible that coping style significantly factors into moderating alcohol use among young male military personnel who reportedly drink more excessively than civilians of the same age. The results indicate that it may be particularly important for the military to assess different stress coping styles ofyoung male military personnel so as to limit excessive drinking as well as to promote individual wellness and improve job performance. [source] Modelling method effects as individual causal effectsJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES A (STATISTICS IN SOCIETY), Issue 1 2008Steffi Pohl Summary., Method effects often occur when different methods are used for measuring the same construct. We present a new approach for modelling this kind of phenomenon, consisting of a definition of method effects and a first model, the method effect model, that can be used for data analysis. This model may be applied to multitrait,multimethod data or to longitudinal data where the same construct is measured with at least two methods at all occasions. In this new approach, the definition of the method effects is based on the theory of individual causal effects by Neyman and Rubin. Method effects are accordingly conceptualized as the individual effects of applying measurement method j instead of k. They are modelled as latent difference scores in structural equation models. A reference method needs to be chosen against which all other methods are compared. The model fit is invariant to the choice of the reference method. The model allows the estimation of the average of the individual method effects, their variance, their correlation with the traits (and other latent variables) and the correlation of different method effects among each other. Furthermore, since the definition of the method effects is in line with the theory of causality, the method effects may (under certain conditions) be interpreted as causal effects of the method. The method effect model is compared with traditional multitrait,multimethod models. An example illustrates the application of the model to longitudinal data analysing the effect of negatively (such as ,feel bad') as compared with positively formulated items (such as ,feel good') measuring mood states. [source] Chain graph models and their causal interpretations,JOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES B (STATISTICAL METHODOLOGY), Issue 3 2002Steffen L. Lauritzen Chain graphs are a natural generalization of directed acyclic graphs and undirected graphs. However, the apparent simplicity of chain graphs belies the subtlety of the conditional independence hypotheses that they represent. There are many simple and apparently plausible, but ultimately fallacious, interpretations of chain graphs that are often invoked, implicitly or explicitly. These interpretations also lead to flawed methods for applying background knowledge to model selection. We present a valid interpretation by showing how the distribution corresponding to a chain graph may be generated from the equilibrium distributions of dynamic models with feed-back. These dynamic interpretations lead to a simple theory of intervention, extending the theory developed for directed acyclic graphs. Finally, we contrast chain graph models under this interpretation with simultaneous equation models which have traditionally been used to model feed-back in econometrics. [source] | ||||||||||||||||||||||||||||||||||||||||