Statistical Analysis
REGRESSION, EVENT
Data analysis was performed from August 2022 to June 2023. The buprenorphine initiation status of each clinician was modeled as a time-to-event survival process with Cox proportional hazards regression, where the event was the first initiation of buprenorphine by a given physician during the study, referred to as the conversion time. Because buprenorphine prescribing status before the study start date was unknown, this represents a time-to-next event analysis since we could not determine whether a buprenorphine initiation event was a clinician’s first ever initiation of buprenorphine. Social contagion was estimated by using the cumulative number of exposures to buprenorphine initiation as a time-dependent variable to measure of the social force associated with individual likelihood to adopt the practice of prescribing buprenorphine. Two cumulative exposure variables were defined: total cumulative exposures and exposure count in the prior 4 months to account for the fact that exposures before the study start period were not observable. For the 4-month exposure variable, all conversions before 4 months were discarded. To examine nonlinearities in the effect of exposures on hazard of conversion, the cumulative exposure variable was modeled with penalized cubic splines with 2 