Messaging, policy and “credible” votes: do members of Congress vote differently when policy is on the line?

Many recorded roll calls in Congress each year are votes on bills that have no chance of becoming law, or are purely symbolic, or are procedural without policy content. Yet models of voting and measurement models of member preferences make assumptions that vote choices are largely about utility derived from policies. We consider the possibility that votes plausibly connected to policy and votes not plausibly connected to policy may have different data-generating processes and rely on different utility functions. Substantively, similarity across different contexts for policy change implies an importance of messaging over policy. Methodologically, similarity across these contexts is necessary to avoid biasing estimates of member preferences. We find that members’ voting patterns are highly stable across contexts in which policy change is credible and not credible. This indicates that existing measures of ideal points are likely not dramatically biased by the inclusion of policy-irrelevant votes.