Comparative Causal Mediation and Relaxing the Assumption of No Mediator–Outcome Confounding: An Application to International Law and Audience Costs

Abstract

Experiments often include multiple treatments, with the primary goal to compare the causal effects of multiple treatments. While comparing the magnitudes of the average treatment effects (ATEs) is straightforward, there exist few methods to systematically compare the causal anatomies of each treatment-that is, the collection of causal mechanisms underlying each treatment's total effect-in order to understand the sources of their relative magnitudes. This study introduces a framework for comparing the causal anatomies of multiple treatments through the use of causal mediation analysis. The study proposes a set of comparative causal mediation estimands that compare the mediation effects of different treatments via a common mediator. It derives the properties of a set of estimators, which are shown to be consistent (or conservative) under a set of assumptions that do not require the absence of unobserved confounding of the mediator-outcome relationship, which is a strong and nonrefutable assumption that must be made for consistent estimation of individual causal mediation effects. To illustrate the method, this study presents an original application investigating the effect of international legality on the domestic political costs that democratic governments suffer for violating foreign policy commitments.

The Two Faces of Opposition to Chemical Weapons: Sincere Versus Insincere Norm-Holders

“…For example, recent research suggests that vivid information about the effects of WMDs (Koch and Wells 2020) or priming international law and ethical norms (Carpenter and Montgomery 2020) reduces support for their use, which may also increase incentives for insincere norm-holding. On the other hand, if CW are depicted as non-lethal alternatives to more traditional, destructive weapons, then that might increase support for their use and reduce the incentives for preference falsification (Bansak 2020). The intended target of CW attacks could also alter the incentives for or against insincere norm-holding depending on where that target falls on the hierarchy of victims (Tezcür and Horschig 2020).…”

“…Why might some citizens privately support the use of CW? For the same reasons they might support the use of other weapons: because they could provide tactical military advantages (Pauly 2018; Rathbun and Stein 2019); preserve other core values like saving the lives of co-national soldiers (Dolan 2013; Sagan and Valentino 2017; Smetana and Vranka 2020); enhance deterrence; maintain national sovereignty; or, in some people’s minds, provide a potentially more painless method of incapacitating or killing enemy combatants (Bansak 2020). We therefore expect that insincere norm-holding will exist with respect to CW, and test the following observable implication of this argument:…”

Introduction to the Special Issue: Innovations and Current Challenges in Experimental Methods

“…Another improvement was made by Bansak (2020). He presented comparative causal mediation (CCM) estimands that allow for the estimation of the effects of multiple treatments (and a single mediator) and comparisons of their magnitudes.…”

“…Another weakness in testing causal mechanisms is that average causal mediation effects rely on strong assumptions that are often known to be false. Bansak (2020) presented causal mediation estimands that trace the causal anatomies of multiple treatments without the assumption of no unobserved confounding of the mediator–outcome relationship. Acharya, Blackwell, and Sen (2018) also relaxed this assumption in their approach to mediation analysis, which experimentally manipulates the mediator rather than observing it.…”

How NATO Membership Transforms Public Support for War

“…Alliances could also give rise to moral obligations. Mounting evidence shows that moral considerations influence public thinking about foreign policy (14,15,16,17,18,6,19). Having promised to defend members of the alliance, citizens may feel an ethical duty to act.…”