Showing papers by "Keith F. Widaman published in 2003"

On specifying the null model for incremental fit indices in structural equation modeling.

Abstract: In structural equation modeling, incremental fit indices are based on the comparison of the fit of a substantive model to that of a null model. The standard null model yields unconstrained estimates of the variance (and mean, if included) of each manifest variable. For many models, however, the standard null model is an improper comparison model. In these cases, incremental fit index values reported automatically by structural modeling software have no interpretation and should be disregarded. The authors explain how to formulate an acceptable, modified null model, predict changes in fit index values accompanying its use, provide examples illustrating effects on fit index values when using such a model, and discuss implications for theory and practice of structural equation modeling.

Stigma, social risk, and health policy: public attitudes toward HIV surveillance policies and the social construction of illness.

Abstract: Data from a 1999 national telephone survey with a probability sample of English-speaking U.S. adults (N = 1,335) were used to assess how support for HIV surveillance policies is related to AIDS stigma and negative attitudes toward groups disproportionately affected by the epidemic. Anonymous reporting of HIV results to the government was supported by a margin of approximately 2-to-1, but name-based reporting was opposed 3-to-1. Compared with other respondents, supporters of name-based surveillance expressed significantly more negative feelings toward people with AIDS, gay men, lesbians, and injecting drug users. More than one third of all respondents reported that concerns about AIDS stigma would affect their own decision to be tested for HIV in the future. Implications for understanding the social construction of illness and for implementing effective HIV surveillance programs are discussed.

New Methods for the Analysis of Change

Abstract: Methods for measuring and modeling change have been a topic of intense research concern and consternation for the past four decades, if not longer. The classic book Problems in Measuring Change, edited by Chester Harris and published in 1963, cast a pall on the field, and Cronbach and Furby (1970) challenged further the status of change scores. If developmental change is construed as a difference score or change score, the preceding works led many to conclude that experts in statistical methodology had demonstrated that developmental change is too unreliable to be the object of scientific study. But such a summary judgment—reached largely by manipulating equations, not data—seemed to fly in the face of experience by practicing scientists that some children appear to grow at faster rates than others, that aging adults exhibit remarkable variability in their rates of decline. If developmental change is so unreliable, how could developmental change be so apparent, replicable, and tangible? Happily, an avalanche of contributions has been made on the topic of modeling change during the past decade or two. The upshot of these more recent contributions is that, even if the methods for doing so are, or seem, a bit arcane, developmental change should be the object of study and can be modeled reliably. One important contribution that promoted the modeling of change was a volume titled Best Methods for the Analysis of Change: Recent Advances, Unanswered Questions, Future Directions, published in 1991 and edited by Linda Collins and John Horn. The current volume is a valuable follow-up to that effort, surveying advances in methods for analyzing change after a decade of additional work. In the preface to the current volume, Linda Collins and Aline Sayer note that at least one reviewer complained about the title of the 1991 Collins and Horn book, calling a book with a title of “best methods” offensive, presumably because the title implied that methods considered therein had special valued status over methods inadvertently excluded. This observation leads the discerning reader to consider carefully the title of the current volume, New Methods for the Analysis of Change. Are all methods in the book really new? If all methods are indeed new, are they truly notable advances over previously proposed approaches or techniques? Even if one opined that the current volume contains much that is new and valuable, one is tempted to mimic the Baron Brougham and Vaux and observe that, alas, “what is valuable is not new, and what is new is not valuable.” The baron’s wry observation implies a strong inverse relation between novelty and value, and this would be a quite inapt characterization of contributions in the Collins and Sayer book. On the other hand, although the magnitude and valence of the relation between novelty and value is

The Maternal Phenylketonuria International Study: 1984-2002.

Abstract: Objective . The purpose of this report is to review the obstetric medical, psychological, and nutritional aspects and outcome of the women and offspring enrolled in the Maternal Phenylketonuria Study, which was established to assess the efficacy of a phenylalanine (Phe)-restricted diet in preventing the morbidity associated with this disorder. Methods . A total of 382 women with hyperphenylalaninemia (HPA) were enrolled in the study and completed 572 pregnancies. Outcome measures were analyzed with χ 2 , Fisher exact text, analysis of variance, t test, Wilcoxon nonparametric test, and multiple logistic regression. Outcome measures were stratified according to maternal HPA classification and the time when dietary control was achieved. Results . Optimal birth outcomes occurred when maternal blood Phe levels between 120 and 360 μmol/L were achieved by 8 to 10 weeks of gestation and maintained throughout pregnancy (trimester averages of 600 μmol/L). Mothers with mild HPA achieved similar birth outcomes as mothers who were in control preconceptually and those in control by 8 to 10 weeks of pregnancy. Conclusions . Before conception, counseling and early entrance into a prenatal care program is essential in achieving optimal fetal outcome in women with HPA. The achievement of pre- and periconceptional dietary control with a Phe-restricted diet significantly decreased morbidity in the offspring of women with HPA.

The difference engine: a model of diversity in speeded cognition.

Abstract: A theory of diversity in speeded cognition, the difference engine, is proposed, in which information processing is represented as a series of generic computational steps. Some individuals tend to perform all of these computations relatively quickly and other individuals tend to perform them all relatively slowly, reflecting the existence of a general cognitive speed factor, but the time required for response selection and execution is assumed to be independent of cognitive speed. The difference engine correctly predicts the positively accelerated form of the relation between diversity of performance, as measured by the standard deviation for the group, and task difficulty, as indexed by the mean response time (RT) for the group. In addition, the difference engine correctly predicts approximately linear relations between the RTs of any individual and average performance for the group, with the regression lines for fast individuals having slopes less than 1.0 (and positive intercepts) and the regression lines for slow individuals having slopes greater than 1.0 (and negative intercepts). Similar predictions are made for comparisons of slow, average, and fast subgroups, regardless of whether those subgroups are formed on the basis of differences in ability, age, or health status. These predictions are consistent with evidence from studies of healthy young and older adults as well as from studies of depressed and age-matched control groups.

Relation of Prenatal Phenylalanine Exposure to Infant and Childhood Cognitive Outcomes: Results From the International Maternal PKU Collaborative Study

Abstract: Objective. The primary aims of this study were to model the form of the relation between prenatal exposure to phenylalanine (Phe) and measures of offspring intellectual development and to estimate the developmental relations of maternal demographic, pregnancy-related, and perinatal variables on offspring intelligence during infancy and childhood. Methods. The participants were the 413 children and their mothers from the International Maternal PKU Collaborative Study. Results. Results supported a nonlinear relation between prenatal Phe exposure and offspring cognitive outcomes, with damage to the developing fetus if average Phe levels are above approximately 360 μmol/L. Moreover, prenatal Phe exposure had a strong effect on offspring outcomes at 1 year of age and was the only one of the background, pregnancy-related, or perinatal variables to influence directly offspring outcomes at 2, 4, and 7 years of age. Conclusion. The present study was able to document the importance of prenatal exposure to Phe for predicting offspring cognitive outcomes in the presence of other predictors of these outcomes.

Longitudinal effects of fraternal deprivation on life satisfaction and mental health

Abstract: According to a widely accepted view in the social justice literature, fraternal deprivation causes protest, but does not impact the individuals’ well-being, whereas egoistic deprivation impairs the well-being of deprived persons, but does not cause protest. We consider this view incomplete, predict that fraternal deprivation can impair well-being under certain conditions, and suggest that negative emotion and negative social identity are mediating mechanisms for this effect. As part of a longitudinal study of the psychological consequences of German unification, measures for fraternal deprivation, individual life quality, life satisfaction, and mental health were obtained on three occasions of measurement (1996, 1998, 2000) from a de-mographically heterogeneous sample of 1276 East German citizens. Model test and parameter estimation were performed with LISREL. In line with our theoretical predictions, longitudinal effects of fraternal deprivation on life satisfaction and mental health were identified and these effects were independent of an individual’s life quality. The longitudinal effect of indi-vidual life quality on life satisfaction (beta = .10) was about twice as large as the longitudinal effect of fraternal deprivation (beta = -.06) on life satisfaction. The effects of individual life quality and fraternal deprivation on mental health were equal (beta =|.04|). Reasons for the small effect sizes are discussed. It is concluded that fraternal deprivation is no less problem-atic for individuals’ well being than is the quality of their personal living conditions.