Panel-Based Ex Post Facto Design — Longitudinal Causal-Comparative Research

A panel-based ex post facto design tracks the same group of participants across multiple time points to examine how pre-existing differences in an independent variable — one the researcher did not manipulate — are associated with changes in an outcome over time. It merges the temporal depth of panel methodology with the causal-comparative logic of ex post facto research, enabling stronger causal inference than a single cross-sectional snapshot while remaining fully non-experimental.