Patient-driven Information Flow and Practice Style Spillover

How physicians form and update practice styles remains central to understanding persistent variation in care. Using quasi-random patient reallocation following primary care clinic closures in Denmark, I examine whether antibiotic prescribing practice styles are transmitted across clinics through patient mobility. I find that clinics receiving more patients with prior antibiotic use increase prescribing intensity among their existing patients. A twofold increase in incoming patients with prior antibiotic use raises prescribing intensity to existing patients by 2.3 percent. The response is stronger among newer clinics and is accompanied by increased use of diagnostic tests, consistent with physicians learning from the prescribing histories of incoming patients rather than responding only to patient volume. The findings highlight patient mobility as an important, informal channel of information transmission in healthcare markets and show that prescribing practices can diffuse across clinics through patient reallocation. These spillovers have implications for the persistence of practice variation and for the design and evaluation of policies aimed at improving antibiotic stewardship.