Longitudinal designs are frequently encountered in epidemiologic research, particularly in the cardiopulmonary field. Many different statistical models have been proposed for the analysis of longitudinal data in the statistical literature. These include the general linear model, autoregressive models, random effects models, and simple models based on an analysis of slopes over time. Complex models are not widely used in the epidemiologic literature, due mainly to a lack of understanding of their underlying utility and the types of questions that could be answered with complex models that cannot be addressed using simple models. An additional problem is a lack of software available for fitting complex models. The study has important public health implications, since longitudinal data continue to accumulate rapidly and no guidelines are available as to the appropriate methods of analysis for specific research questions. Furthermore, it is often only through the modelling of longitudinal data that processes pertaining to change can be understood. The original aim of the study was to perform a comparative study of statistical models on datasets from nine large epidemiological studies in the cardiopulmonary field in order to develop tools for identifying appropriate classes of statistical models for use in analyzing longitudinal data.