Two-way fixed effects (TWFE) models are ubiquitous in causal panel analysis
in political science. However, recent methodological discussions challenge
their validity in the presence of heterogeneous treatment effects (HTE) and
violations of the parallel trends assumption (PTA). This burgeoning literature
has introduced multiple estimators and diagnostics, leading to confusion among
empirical researchers on two fronts: the reliability of existing results based
on TWFE models and the current best practices. To address these concerns, we
examined, replicated, and reanalyzed 37 articles from three leading political
science journals that employed observational panel data with binary treatments.
Using six newly introduced HTE-robust estimators, we find that although
precision may be affected, the core conclusions derived from TWFE estimates
largely remain unchanged. PTA violations and insufficient statistical power,
however, continue to be significant obstacles to credible inferences. Based on
these findings, we offer recommendations for improving practice in empirical
research