THE DESIGN AND ANALYSIS OF LONGITUDINAL-STUDIES OF DEVELOPMENT AND PSYCHOPATHOLOGY IN CONTEXT - STATISTICAL-MODELS AND METHODOLOGICAL RECOMMENDATIONS

The utility and flexibility of recent advances in statistical methods for the quantitative analysis of developmental data-in particular, the methods of individual growth modeling and survival analysis-are unque stioned by methodologists, but have yet to have a major impact on empi rical research within the field of developmental psychopathology and e lsewhere. In this paper, we show how these new methods provide develop mental psychpathologists with powerful ways of answering their researc h questions about systematic changes over time in individual behavior and about the occurrence and timing of life events. In the first secti on, we present a descriptive overview of each method by illustrating t he types of research questions that each method can address, introduci ng the statistical models, and commenting on methods of model fitting, estimation, and interpretation. In the following three sections, we o ffer six concrete recommendations for developmental psychopathologists hoping to use these methods. First, we recommend that when designing studies, investigators should increase the number of waves of data the y collect and consider the use of accelerated longitudinal designs. Se cond, we recommend that when selecting measurement strategies, investi gators should strive to collect equatable data prospectively on all ti me-varying measures and should never standardize their measures before analysis. Third, we recommend that when specifying statistical models , researchers should consider a variety of alternative specifications for the time predictor and should test for interactions among predicto rs, particularly interactions between substantive predictors and time. Our goal throughout is to show that these methods are essential tools for answering questions about life-span developmental processes in bo th normal and atypical populations and that their proper use will help developmental psychopathologists and others illuminate how important contextual variables contribute to various pathways of development.