Do Treaties Constrain or Screen? Selection Bias and Treaty Compliance

Much recent research has found that states generally comply with the treaties they sign. The implications of this finding, however, are unclear: do states comply because the legal commitment compels them to do so, or because of the conditions that led them to sign? Drawing from previous research in this Review on Article VIII of the IMF Treaty (Simmons 2000a), I examine the problem of selection bias in the study of treaty compliance. To understand how and whether international legal commitments affect state behavior, one must control for all sources of selection into the treaty—including those that are not directly observable. I develop a statistical method that controls for such sources of selection and find considerable evidence that the unobservable conditions that lead states to make the legal commitment to Article VIII have a notable impact on their propensity to engage in compliant behavior. The results suggest that the international legal commitment has little constraining power independent of the factors that lead states to sign.