Two-way fixed effects (TWFE) models are widely used in political science to establish causality, but recent methodological discussions highlight their limitations under heterogeneous treatment effects (HTE) and violations of the parallel trends (PT) assumption. This growing literature has introduced new estimators and diagnostics, causing confusion among researchers about the reliability of existing results and best practices. To address these concerns, we replicated and reanalyzed 49 articles from leading journals using TWFE models for observational panel data with binary treatments. Using six HTE-robust estimators, diagnostic tests, and sensitivity analyses, we find: (i) HTE-robust estimators yield qualitatively similar but highly variable results; (ii) while a few studies show clear signs of PT violations, many lack evidence to support this assumption; and (iii) many studies are underpowered when accounting for HTE and potential PT violations. We emphasize the importance of strong research designs and rigorous validation of key identifying assumptions.

翻译：双向固定效应（TWFE）模型在政治学中被广泛用于建立因果关系，但近期的研究方法讨论揭示了其在异质性处理效应（HTE）和违反平行趋势（PT）假设下的局限性。这一不断增长的文献引入了新的估计量和诊断方法，导致研究者对现有结果的可靠性和最佳实践感到困惑。为应对这些问题，我们复制并再分析了49篇使用TWFE模型处理二元处理观测面板数据的顶尖期刊文章。通过使用六种HTE稳健估计量、诊断检验和敏感性分析，我们发现：（i）HTE稳健估计量产生性质相似但高度可变的结果；（ii）虽然少数研究显示出明显的PT违反迹象，但许多研究缺乏支持该假设的证据；（iii）在考虑HTE和潜在的PT违反时，许多研究的统计功效不足。我们强调强健的研究设计以及对关键识别假设进行严格验证的重要性。