Mediation analysis uses measures of hypothesized mediating variables to test theory for how a treatment achieves effects on outcomes and to improve subsequent treatments by identifying the most efficient treatment components. Most current mediation analysis methods rely on untested distributional and functional form assumptions for valid…

One can distinguish statistical models used in causal modeling from the causal interpretations that align them with substantive hypotheses. Causal modeling typically assumes an efficient causal interpretation of the statistical model. Causal modeling can also make use of mereological causal interpretations in which the state of the parts…

It is shown that, for equivalent structural equation models that have been extended to multigroup models, imposing cross-group equality constraints on no parameters, all parameters, or any number of parameters for which the models are identical preserves the model equivalence property. Results are illustrated with two-group cognitive intervention…

Individually randomized treatments are often administered within a group setting. As a consequence, outcomes for treated individuals may be correlated due to provider effects, common experiences within the group, and/or informal processes of socialization. In contrast, it is often reasonable to regard outcomes for control participants as…

There is evidence to suggest that the effects of behavioral interventions may be limited to specific types of individuals, but methods for evaluating such outcomes have not been fully developed. This study proposes the use of finite mixture models to evaluate whether interventions, and, specifically, group randomized trials, impact participants…

Introduces this special issue on multilevel models. The first two articles examine the application of multilevel modeling (MLM) in the evaluation of large-scale multi-site interventions. The next two articles focus on developmental and longitudinal data analysis, and the last two describe innovative applications of MLM. (SLD)

Describes the use of multilevel models (MLMs) for studies in which individuals are randomized by groups to treatment condition. Uses data from the Safer Choices study, an evaluation of a theory-based multi-component program to prevent sexually transmitted diseases and pregnancy, to illustrate the application of MLMs for both continuous and…

Describes the application of multilevel statistical models to the evaluation of a multi-site community-based intervention and explicates key issues in the design,analysis, and presentation of results. The initiative described, "Fighting Back, is designed to reduce the demand for illegal drugs and alcohol in a community. (SLD)

The ability of 248 older adults to improve their performance on fluid intelligence tests, with or without tutor-guided instruction in cognitive skills, was studied using multidimensional longitudinal structural equation models. Results suggest considerable plasticity in adult intellectual function and the capacity to improve performance. (SLD)