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1.
Mediation models are commonly used to identify the mechanisms through which one variable influences another. Among longitudinal mediation methods, latent difference score mediation stands out due to its unique ability to capture nonlinear change over time. However, there is limited information regarding sample size demands to achieve adequate power with this method, resulting in few applications of latent difference score mediation. To address this limitation, the current study presents empirically supported sample size guidelines for 10 common latent difference score mediation structural models and 9 unique population models. The results of this study offer researchers with a set of representative sample estimates that may be used when designing studies or seeking funding.  相似文献   

2.
The latent growth curve modeling (LGCM) approach has been increasingly utilized to investigate longitudinal mediation. However, little is known about the accuracy of the estimates and statistical power when mediation is evaluated in the LGCM framework. A simulation study was conducted to address these issues under various conditions including sample size, effect size of mediated effect, number of measurement occasions, and R 2 of measured variables. In general, the results showed that relatively large samples were needed to accurately estimate the mediated effects and to have adequate statistical power, when testing mediation in the LGCM framework. Guidelines for designing studies to examine longitudinal mediation and ways to improve the accuracy of the estimates and statistical power were discussed.  相似文献   

3.
Abstract

When well-implemented, mediation analyses play a critical role in probing theories of action because their results help lay the ground work for the critical development of a treatment and the iterative advancement of theories that are foundational to a discipline. Despite strong interest in designs that incorporate mediation, few studies have developed effective and efficient strategies to plan experiments examining multilevel mediation. We probe several design strategies for cluster-randomized designs and derive sampling plans that maximize power under cost constraints. The results suggest that among the more durable design strategies for mediation is covariance adjustment on variables predictive of the outcome and optimal sample allocation. The statistical power and optimal sample allocation results are implemented in the R package PowerUpR.  相似文献   

4.
Structured means analysis is a very useful approach for testing hypotheses about population means on latent constructs. In such models, a z test is most commonly used for testing the statistical significance of the relevant parameter estimates or of the differences between parameter estimates, where a z value is computed based on the asymptotic standard error estimate associated with the parameter of interest. In the current article, a series of population analyses demonstrate that the z tests for latent mean structure parameters or, more directly, the standard error estimates upon which those z tests are based are, not invariant to how factors are scaled. As such, circumstances exist in which latent mean inference is compromised solely as a result of scaling decisions. This problem is illustrated in the context of between-subjects (i.e., multisample) latent means models and within-subjects latent means models. Recommendations for practice are also offered.  相似文献   

5.
Numerous theoretical structures involve the concept of mediation, the mechanism that accounts for the relation between the predictor and the criterion. The, empirical interpretation of mediation has employed multiple independent models to assess components of the overall structure in a piecemeal manner. This article discusses various limitations of using this independent approach and proposes the use of structural equation modeling (SEM) as an alternative. The article furthermore distinguishes current limitations in using SEM software for assessing mediation in complex structures and presents a strategy for supplemental details that more accurately measure the magnitude of mediational effects, in particular, specific indirect effects.  相似文献   

6.
Models to assess mediation in the pretest–posttest control group design are understudied in the behavioral sciences even though it is the design of choice for evaluating experimental manipulations. The article provides analytical comparisons of the four most commonly used models to estimate the mediated effect in this design: analysis of covariance (ANCOVA), difference score, residualized change score, and cross-sectional model. Each of these models is fitted using a latent change score specification and a simulation study assessed bias, Type I error, power, and confidence interval coverage of the four models. All but the ANCOVA model make stringent assumptions about the stability and cross-lagged relations of the mediator and outcome that might not be plausible in real-world applications. When these assumptions do not hold, Type I error and statistical power results suggest that only the ANCOVA model has good performance. The four models are applied to an empirical example.  相似文献   

7.
This article presents several longitudinal mediation models in the framework of latent growth curve modeling and provides a detailed account of how such models can be constructed. Logical and statistical challenges that might arise when such analyses are conducted are also discussed. Specifically, we discuss how the initial status (intercept) and change (slope) of the putative mediator variable can be appropriately included in the causal chain between the independent and dependent variables in longitudinal mediation models. We further address whether the slope of the dependent variable should be controlled for the dependent variable's intercept to improve the conceptual relevance of the mediation models. The models proposed are illustrated by analyzing a longitudinal data set. We conclude that for certain research questions in developmental science, a multiple mediation model where the dependent variable's slope is controlled for its intercept can be considered an adequate analytical model. However, such models also show several limitations.  相似文献   

8.
This study examined the transactional interplay among children's negative family representations, visual processing of negative emotions, and externalizing symptoms in a sample of 243 preschool children (Mage = 4.60 years). Children participated in three annual measurement occasions. Cross‐lagged autoregressive models were conducted with multimethod, multi‐informant data to identify mediational pathways. Consistent with schema‐based top‐down models, negative family representations were associated with attention to negative faces in an eye‐tracking task and their externalizing symptoms. Children's negative representations of family relationships specifically predicted decreases in their attention to negative emotions, which, in turn, was associated with subsequent increases in their externalizing symptoms. Follow‐up analyses indicated that the mediational role of diminished attention to negative emotions was particularly pronounced for angry faces.  相似文献   

9.
Mediation is one concept that has shaped numerous theories. The list of problems associated with mediation models, however, has been growing. Mediation models based on cross-sectional data can produce unexpected estimates, so much so that making longitudinal or causal inferences is inadvisable. Even longitudinal mediation models have faults, as parameter estimates produced by these models are specific to the lag between observations, leading to much debate over appropriate lag selection. Using continuous time models (CTMs) rather than commonly employed discrete time models, one can estimate lag-independent parameters. We demonstrate methodology that allows for continuous time mediation analyses, with attention to concepts such as indirect and direct effects, partial mediation, the effect of lag, and the lags at which relations become maximal. A simulation compares common longitudinal mediation methods with CTMs. Reanalysis of a published covariance matrix demonstrates that CTMs can be fit to data used in longitudinal mediation studies.  相似文献   

10.
Researchers often use measures of the frequency of self-regulated learning (SRL; Zimmerman, American Educational Research Journal, 45(1), 166–183, 2000) processing as a predictor of learning gains. These frequency data, which are really counts of SRL processing events, are often non-normally distributed, and the accurate analysis of these data requires the use of specialized statistical models. In this study, we demonstrate how to implement and interpret count statistical models in path and latent profile analyses to investigate the role of SRL as a mediator of the relation between pretest and posttest conceptual understanding. Our findings from a sample of 170 college students using a computer to learn about the circulatory system show that SRL does mediate the aforementioned relation, and that count models are a more accurate representation of SRL processing data than standard analysis models based on ordinary least squares estimation. The results of our path analyses revealed which specific SRL processes were related to learning, above and beyond the effect of prior knowledge. Our latent profile analysis revealed two groups of participants, indicative of Brophy’s (2004) model of schematic and aschematic learners. We conclude with implications and future directions for basic and applied SRL research.  相似文献   

11.
A non-arbitrary method for the identification and scale setting of latent variables in general structural equation modeling is introduced. This particular technique provides identical model fit as traditional methods (e.g., the marker variable method), but it allows one to estimate the latent parameters in a nonarbitrary metric that reflects the metric of the measured indicators. This technique, therefore, is particularly useful for mean and covariance structures (MACS) analyses, where the means of the indicators and latent constructs are of key interest. By introducing this alternative method of identification and scale setting, researchers are provided with an additional tool for conducting MACS analyses that provides a meaningful and nonarbitrary scale for the estimates of the latent variable parameters. Importantly, this tool can be used with single-group single-occasion models as well as with multiple-group models, multiple-occasion models, or both.  相似文献   

12.
Research demonstrates that children exposed to domestic violence experience a myriad of internalising and externalising symptoms. The current study examines this pathway within a Cambodian sample, specifically determining if the effect of witnessing domestic violence on the child’s tendency to bully or to be bullied is mediated by symptoms of posttraumatic stress disorder (PTSD). The PTSD Checklist – Civilian Version, a revised version of a12-item bullying and victimisation questionnaire, and the Revised Conflict Tactics Scale were administered to 206 high school students in Phnom Penh. A significant mediational effect of PTSD symptoms was found for victimisation (being bullied); no such mediational model was supported for bullying as the outcome variable. However, controlling for emotional, physical, and sexual child abuse resulted in the mediation effect being non-significant. Implications and directions for future research are discussed.  相似文献   

13.
Conventionally, moderated mediation analysis is conducted through adding relevant interaction terms into a mediation model of interest. In this study, we illustrate how to conduct moderated mediation analysis by directly modeling the relation between the indirect effect components including a and b and the moderators, to permit easier specification and interpretation of moderated mediation. With this idea, we introduce a general moderated mediation model that can be used to model many different moderated mediation scenarios including the scenarios described in Preacher, Rucker, and Hayes (2007). Then we discuss how to estimate and test the conditional indirect effects and to test whether a mediation effect is moderated using Bayesian approaches. How to implement the estimation in both BUGS and Mplus is also discussed. Performance of Bayesian methods is evaluated and compared to that of frequentist methods including maximum likelihood (ML) with 1st-order and 2nd-order delta method standard errors and mL with bootstrap (percentile or bias-corrected confidence intervals) via a simulation study. The results show that Bayesian methods with diffuse (vague) priors implemented in both BUGS and Mplus yielded unbiased estimates, higher power than the ML methods with delta method standard errors, and the ML method with bootstrap percentile confidence intervals, and comparable power to the ML method with bootstrap bias-corrected confidence intervals. We also illustrate the application of these methods with the real data example used in Preacher et al. (2007). Advantages and limitations of applying Bayesian methods to moderated mediation analysis are also discussed.  相似文献   

14.
Two studies examined whether hope partially mediates the relationship between socioeconomic status (SES) and academic achievement. Guided by recent theoretical formulations about social class and the social cognitive process, in Study 1 a mediational pathway from SES to academic achievement via hope was documented in a diverse sample of adolescents. The mediational pathway was replicated in Study 2 in a minority sample of high school students. In both studies, hope was found to partially mediate the relationship between SES and grade point average. In addition, the unique contribution of hope to academic achievement replicated across the 2 studies, indicating that the additional stressors and challenges associated with being a minority did not affect the mediation. These results have implications for achievement gap interventions.  相似文献   

15.
This study examined whether childhood interparental conflict moderated the mediational pathway involving adolescent exposure to interparental conflict, their negative emotional reactivity to family conflict, and their psychological problems in a sample of 235 children (Mage = 6 years). Significant moderated-mediation findings indicated that the mediational path among Wave 4 interparental conflict during adolescence, change in youth negative reactivity (Waves 4–5), and their psychological problems (Waves 4–6) was significant for teens who experienced low, rather than high, levels of childhood interparental conflict (Waves 1–3). Supporting the stress sensitization model, analyses showed that adolescents exposed to high interparental conflict during childhood evidenced greater increases in negative reactivity than their peers when recent parental conflicts were mild.  相似文献   

16.
Latent growth curve mediation models are increasingly used to assess mechanisms of behavior change. For latent growth mediation model, like any another mediation model, even with random treatment assignment, a critical but untestable assumption for valid and unbiased estimates of the indirect effects is that there should be no omitted variable that confounds indirect effects. One way to address this untestable assumption is to conduct sensitivity analysis to assess whether the inference about an indirect effect would change under varying degrees of confounding bias. We developed a sensitivity analysis technique for a latent growth curve mediation model. We compute the biasing effect of confounding on point and confidence interval estimates of the indirect effects in a structural equation modeling framework. We illustrate sensitivity plots to visualize the effects of confounding on each indirect effect and present an empirical example to illustrate the application of the sensitivity analysis.  相似文献   

17.
We evaluated the statistical power of single-indicator latent growth curve models to detect individual differences in change (variances of latent slopes) as a function of sample size, number of longitudinal measurement occasions, and growth curve reliability. We recommend the 2 degree-of-freedom generalized test assessing loss of fit when both slope-related random effects, the slope variance and intercept-slope covariance, are fixed to 0. Statistical power to detect individual differences in change is low to moderate unless the residual error variance is low, sample size is large, and there are more than four measurement occasions. The generalized test has greater power than a specific test isolating the hypothesis of zero slope variance, except when the true slope variance is close to 0, and has uniformly superior power to a Wald test based on the estimated slope variance.  相似文献   

18.
Little research has examined factors influencing statistical power to detect the correct number of latent classes using latent profile analysis (LPA). This simulation study examined power related to interclass distance between latent classes given true number of classes, sample size, and number of indicators. Seven model selection methods were evaluated. None had adequate power to select the correct number of classes with a small (Cohen's d = .2) or medium (d = .5) degree of separation. With a very large degree of separation (d = 1.5), the Lo–Mendell–Rubin test (LMR), adjusted LMR, bootstrap likelihood ratio test, Bayesian Information Criterion (BIC), and sample-size-adjusted BIC were good at selecting the correct number of classes. However, with a large degree of separation (d = .8), power depended on number of indicators and sample size. Akaike's Information Criterion and entropy poorly selected the correct number of classes, regardless of degree of separation, number of indicators, or sample size.  相似文献   

19.
This study is a methodological-substantive synergy, demonstrating the power and flexibility of exploratory structural equation modeling (ESEM) methods that integrate confirmatory and exploratory factor analyses (CFA and EFA), as applied to substantively important questions based on multidimentional students' evaluations of university teaching (SETs). For these data, there is a well established ESEM structure but typical CFA models do not fit the data and substantially inflate correlations among the nine SET factors (median rs = .34 for ESEM, .72 for CFA) in a way that undermines discriminant validity and usefulness as diagnostic feedback. A 13-model taxonomy of ESEM measurement invariance is proposed, showing complete invariance (factor loadings, factor correlations, item uniquenesses, item intercepts, latent means) over multiple groups based on the SETs collected in the first and second halves of a 13-year period. Fully latent ESEM growth models that unconfounded measurement error from communality showed almost no linear or quadratic effects over this 13-year period. Latent multiple indicators multiple causes models showed that relations with background variables (workload/difficulty, class size, prior subject interest, expected grades) were small in size and varied systematically for different ESEM SET factors, supporting their discriminant validity and a construct validity interpretation of the relations. A new approach to higher order ESEM was demonstrated, but was not fully appropriate for these data. Based on ESEM methodology, substantively important questions were addressed that could not be appropriately addressed with a traditional CFA approach.  相似文献   

20.
The objective of this study is to add to the extant literature on graduate attributes by examining the mediating role of global/moral citizenship and lifelong learning attributes in the relation between students' scholarship attributes and their academic self-directedness in a higher-education open distance learning (ODL) environment. The Graduate Skills and Attributes Scale and Adult Learner Self-directedness Scale were administered to a stratified proportional random sample of N?=?1102 undergraduate ODL students in the economic and management sciences field. Data analyses consisted of an analysis of correlations and two simple mediational models. The results revealed significant direct and indirect effects between the variables. The academic self-directedness of the participants was positively influenced by their scholarship, global/moral citizenship and lifelong learning attributes. The influence of scholarship attributes on academic self-directedness is significantly mediated through global/moral citizenship and lifelong learning attributes. These findings contribute new knowledge that informs the design of teaching and learning activities aimed at enhancing the academic self-directedness of students pursuing educational studies in an ODL environment.  相似文献   

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