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The Constraining Power of International Treaties: Theory and Methods


We acknowledge the contribution of von Stein (2005) in calling attention to the very real problem of selection bias in estimating treaty effects. Nonetheless, we dispute both von Stein's theoretical and empirical conclusions. Theoretically, we contend that treaties can both screen and constrain simultaneously, meaning that findings of screening do nothing to undermine the claim that treaties constrain state behavior as well. Empirically, we question von Stein's estimator on several grounds, including its strong distributional assumptions and its statistical inconsistency. We then illustrate that selection bias does not account for much of the difference between Simmons's (2000) and von Stein's (2005) estimated treaty effects, and instead reframe the problem as one of model dependency. Using a preprocessing matching step to reduce that dependency, we then illustrate treaty effects that are both substantively and statistically significant—and that are quite close in magnitude to those reported by Simmons.

Corresponding author
Beth A. Simmons is Professor, Department of Government, Harvard University, 1033 Massachusetts Avenue, Cambridge, MA 02139 (
Daniel J. Hopkins is a Ph.D. student, Department of Government, Harvard University, Littauer Center, North Yard, Cambridge, MA 02138 (
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American Political Science Review
  • ISSN: 0003-0554
  • EISSN: 1537-5943
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