Marginal maximum likelihood estimation of item parameters: Application of an EM algorithm

Maximum likelihood estimation of item parameters in the marginal distribution, integrating over the distribution of ability, becomes practical when computing procedures based on an EM algorithm are used. By characterizing the ability distribution empirically, arbitrary assumptions about its form are avoided. The Em procedure is shown to apply to general item-response models lacking simple sufficient statistics for ability. This includes models with more than one latent dimension.Supported in part by NSF grant BNS 7912417 to the University of Chicago and by SSRC (UK) grant HR6132 to the University of Lancaster.We are indebted to Mark Reiser and Robert Gibbons for computer programming. David Thissen clarified a number of points in an earlier draft.     

中介效应检验程序及其应用

讨论了中介变量以及相关概念、中介效应的估计；比较了检验中介效应的主要方法；提出了一个检验程序，它包含了依次检验和Sobel检验。该程序检验的第一类和第二类错误率之和通常比单一检验方法小，既可以做部分中介检验，也可以做完全中介检验。作为示范例子，引入中介变量研究学生行为对同伴关系的影响。     

Some critical observations of the test information function as a measure of local accuracy in ability estimation

The test information function serves important roles in latent trait models and in their applications. Among others, it has been used as the measure of accuracy in ability estimation. A question arises, however, if the test information function is accurate enough for all meaningful levels of ability relative to the test, especially when the number of test items is relatively small (e.g., less than 50). In the present paper, using the constant information model and constant amounts of test information for a finite interval of ability, simulated data were produced for eight different levels of ability and for twenty different numbers of test items ranging between 10 and 200. Analyses of these data suggest that it is desirable to consider some modification of the test information function when it is used as the measure of accuracy in ability estimation.     

A longitudinal model of executive function development from birth through adolescence in children born very or extremely preterm

Executive function deficits are often reported as a specific weakness in preterm children. Yet, executive function development is still not fully understood. In a prospective longitudinal study, 115 preterm born children, ≤31 weeks of gestation, were recruited at birth and subject to neuropsychological assessments at ages 5.5 and 18 years. By applying Miyake and colleagues’ integrative framework of executive function to our data, two core components of executive function, working memory and cognitive flexibility, were identified through confirmatory factor analysis. Developmental stability was investigated in a serial multiple mediator structural equation model. Biological, medical, and social factors as well as mental development at 10 months were entered as predictors. Both components of executive function were highly stable from 5.5 to 18 years. Gestational age, intrauterine growth, lack of perinatal medical complications, and female sex were positively related to mental development at 10 months, which together with parental education influenced both core executive functions at 5.5 years. Working memory at 5.5 years mediated outcome in working memory at 18 years. In addition to the mediation of cognitive flexibility at 5.5 years, perinatal medical complications and restricted intrauterine growth had a continued direct negative impact on cognitive flexibility at 18 years. The application of a theoretical framework added to our understanding of executive function development in preterm born children. The study supports early identification of executive deficits among children born preterm, as deficits are unlikely to diminish with maturation.     

Process,mechanism, and explanation related to externalizing behavior in developmental psychopathology

Advances in conceptualization and statistical modeling, on the one hand, and enhanced appreciation of transactional pathways, gene–environment correlations and interactions, and moderator and mediator variables, on the other, have heightened awareness of the need to consider factors and processes that explain the development and maintenance of psychopathology. With a focus on attentional problems, impulsivity, and disruptive behavior patterns, I address the kinds of conceptual approaches most likely to lead to advances regarding explanatory models in the field. Findings from my own research program on processes and mechanisms reveal both promise and limitations. Progress will emanate from use of genetically informative designs, blends of variable and person-centered research, explicit testing of developmental processes, systematic approaches to moderation and mediation, exploitation of natural experiments, and the conduct of prevention and intervention trials designed to accentuate explanation as well as outcome. In all, breakthroughs will occur only with advances in translational research—linking basic and applied science—and with the further development of transactional, systemic approaches to explanation.     

Cognitive mediation of intervention effects on physical exercise: Causal models for the adoption and maintenance stage

Objective: To investigate how the effects of a group-based intervention program (MoVo-LISA) on exercise behaviour were mediated by cognitive variables. Different causal models mapping the short-term (adoption) and long-term (maintenance) intervention effects were tested using path analyses.

Design: N?=?220 in-patients of a rehabilitation clinic were assigned to an usual care or intervention group (quasi-experimental design). Questionnaire-based assessment was conducted at baseline; discharge; and at six weeks, six months and 12 months post discharge.

Measures: The potential mediator variables were outcome expectations, self-efficacy, strength of goal intention (intention strength), self-concordance, action planning and barrier management.

Results: Observed intervention effects on exercise behaviour (p?<?0.05) were mediated by intention strength at the adoption and maintenance stages, by action planning only at the adoption, and by barrier management only at the maintenance stage. Self-efficacy and outcome expectations were only indirectly involved in these mediations by affecting intention strength and self-concordance.

Conclusion: This is the first study to track the cognitive mediation processes of intervention effects on exercise behaviour over a long time-period by differentiating the adoption and maintenance stages of behaviour change. The findings emphasise the importance of deconstructing intervention effects (modifiability vs. predictive power of a mediator) to develop more effective interventions.     

Depression as a mediator of negative cognitive style and hopelessness in stress generation

Over the past 20 years, there has been considerable interest in the role of cognitive factors in the stress generation process. Generally, these studies find that depressed individuals, or individuals at cognitive risk for depression, are more likely to experience stressful life events that are in part influenced by their own characteristics and behaviours (i.e., negative dependent events). However, there is still much to be learnt about the mediators of these effects. For example, does the development of depression symptoms explain why individuals at cognitive risk for depression experience increased negative dependent events? Or, is it that increases in cognitive risk explain why depressed individuals experience increased negative dependent events? To explore these questions, a short‐term prospective study was conducted with 209 college students who were given measures of depression, depressogenic risk factors (i.e., negative cognitive style and hopelessness), and negative dependent events at two time points 6 weeks apart. Support was found for three models: (1) depression symptoms mediated the relationship between negative cognitive style and negative dependent events; (2) depression symptoms mediated the relationship between hopelessness and negative dependent events; and (3) first hopelessness and then depression symptoms mediated the relationship between negative cognitive style and negative dependent events in a multiple‐step model. In contrast, the reverse models were not confirmed, suggesting specificity in the direction of the mediational sequence.     

Cognitive Mediators of Treatment for Social Anxiety Disorder: Comparing Acceptance and Commitment Therapy and Cognitive-Behavioral Therapy

Objective

To assess the relationship between session-by-session mediators and treatment outcomes in traditional cognitive-behavioral therapy (CBT) and acceptance and commitment therapy (ACT) for social anxiety disorder.

Method

Session-by-session changes in negative cognitions (a theorized mediator of CBT) and experiential avoidance (a theorized mediator of ACT) were assessed in 50 adult outpatients randomized to CBT (n = 25) or ACT (n = 25) for DSM-IV social anxiety disorder.

Results

Multilevel modeling analyses revealed significant nonlinear decreases in the proposed mediators in both treatments, with ACT showing steeper decline than CBT at the beginning of treatment and CBT showing steeper decline than ACT at the end of treatment. Curvature (or the nonlinear effect) of experiential avoidance during treatment significantly mediated posttreatment social anxiety symptoms and anhedonic depression in ACT, but not in CBT, with steeper decline of the Acceptance and Action Questionnaire at the beginning of treatment predicting fewer symptoms in ACT only. Curvature of negative cognitions during both treatments predicted outcome, with steeper decline of negative cognitions at the beginning of treatment predicting lower posttreatment social anxiety and depressive symptoms.

Conclusions

Rate of change in negative cognitions at the beginning of treatment is an important predictor of change across both ACT and CBT, whereas rate of change in experiential avoidance at the beginning of treatment is a mechanism specific to ACT.     

Emotional labor and burnout among female teachers: Work–family conflict as mediator

With the increasing number of women in the workforce, there is a need to understand how the interrelationship between emotions and the demands of work and family influence their well‐being. This study examined how emotional labor [surface acting (SA) and deep acting] and work–family conflict contribute to explaining variance in burnout (emotional exhaustion and depersonalization). In a sample of 102 married, female Malay teachers, with at least one child living at home, results showed that SA was positively associated with emotional exhaustion and depersonalization. The results also showed that work–family conflict mediated the relationship between emotional labor and burnout. However, no moderation effect of work–family on the SA–burnout relationship was found. The results are discussed with respect to the general literature on the stress–strain relation and work–family conflict.     

Exploratory Mediation Analysis of Dichotomous Outcomes via Regularization

Abstract

Exploratory mediation analysis via regularization, or XMed, is a recently developed technique that allows one to identify potential mediators of a process of interest. However, as currently implemented, it can only be applied to continuous outcomes. We extend this method to allow application to dichotomous outcomes, including both mediators and dependent variables. Simulation results show that XMed can achieve the same sensitivity as more conventional methods for mediation analysis such as the Sobel test, percentile bootstrap, and bias-corrected bootstrap, but in general requires only half the sample size to do so. We demonstrate the implementation of this approach using an illustrative example examining the relationship between youth behavioral/emotional problems and alcohol use.