Why state constitutions differ in their treatment of same-sex marriage

Some states treat a same-sex marriage as legally equivalent to a marriage between a man and a woman. Other states constitutionally prohibit legal recognition of same-sex marriages. In all states that have constitutional restrictions against same-sex marriage, the restrictions were passed by a popular vote. A rationale for allowing citizens to vote on constitutional amendments is to produce constitutional outcomes that reflect variations in attitudes across states. We reexamine the amendment-attitude relationship and find it to be weaker than expected. We then develop an alternate explanation that focuses on procedural variations in how states amend their constitutions. Explicitly integrating key institutional variations into an empirical model with attitudinal data yields an improved explanation of why the constitutions of states with similar public attitudes treat same-sex marriages so differently. Our findings have important implications for people who wish to understand and/or change the future status of same-sex couples in state constitutions.