1 Introduction Definition 2 The Purposes of Longitudinal Research Age, Period, and Cohort Effects Causal Relationships Serendipity and Intentionality in Longitudinal Data 3 Designs for Longitudinal Data Collection Not-Quite-Longitudinal Designs Total Population Designs Repeated Cross-Sectional Designs Revolving Panel Designs Longitudinal Panel Designs Other Variations 4 Issues in Longitudinal Research Genesis Versus Prediction Changes in Measurement Over Time Panel Attrition Treatment of Missing Data in Longitudinal Research Repeated Measurement and Panel Conditioning Respondent Recall The Costs of Longitudinal Research 5 Longitudinal Analysis Longitudinal versus Cross-Sectional Statistical Methods Types of Longitudinal Causal Models Measuring Change Deterministic versus Probabilistic Models Pooling Cross-Sectional and Time Series Data Time Series Analysis Methods for Short Time Serieswith Many Cases Methods for Long Time Seres with Many Cases Longitudinal Versus Cross-Sectional Data and Analysis Notes References.