Collaborative diffusion: The dynamics of policy output in <scp>COVID</scp> ‐19 interstate compacts

Abstract Interstate compacts are formal structures through which multiple states work together towards a common goal or shared agenda. Previous research on compacts focuses almost exclusively on the decision to join the compact, leaving questions on post‐formation diffusion patterns unexplored. We use a unique case of three interstate compacts that form simultaneously around the same issue—the COVID‐19 pandemic—to test how policy diffuses within compacts. We employ a novel diffusion methodology, network event history analysis (NEHA), to determine the role of compact membership in policy activity. We find that compact member states are no more active in adopting policy than non‐members, but that non‐member states use compacts to free ride when making their own adoption choices. We find that compacts serve to establish members as leaders, as non‐members' policy adoptions are strongly driven by the adoptions of compact members. We also find COVID‐19 policy diffusion to be strongly driven by state ideology.