We conduct a meta-analysis of instrumental variable (IV) designs published in three top journals in Political Science (APSR, AJPS, JOP) and identify several concerning patterns:
- Researchers often overestimate the strength of their instruments due to non-i.i.d. error structures such as clustering.
- 2SLS estimates are often highly uncertainl; commonly used t-test frequently underestimate the uncertainties.
- 2SLS estimates are much larger in magnitude than OLS estimates in many observational studies and their ratio is inversely related to the strength of the instrument, suggesting violations of unconfoundedness or the exclusion restriction in the former.
Here, we present replication results for each paper we reanalyzed.