The unit of analysis for this equation is the jurisdiction i eligible to adopt a policy (i.e., the jurisdiction that has not yet adopted the policy) in a particular year t. The dependent variable—ADOPTi,t—is the probability that jurisdiction i will adopt the policy in year t. EXTERNALi,t denotes variables reflecting diffusion effects on jurisdiction i at time t; thus, these variables would measure the behavior of other jurisdictions at time t, or in the recent past.
