This document discusses key elements of research design, including causation, units of analysis, and the time dimension. It explains that causation in social science is probabilistic and there are two models of explanation - ideographic and nomothetic. The main units of analysis are individuals, groups, organizations, and social artifacts. Researchers must avoid ecological and individualistic fallacies by properly matching units of analysis. Research can examine a single point in time via cross-sectional studies or observe changes over time through longitudinal, trend, cohort, and panel studies. Retrospective studies can sometimes approximate longitudinal designs.