The Diversity of Concentrated Prescribing Behavior: An Application to Antipsychotics

Physicians prescribing drugs for patients with schizophrenia and related conditions are remarkably concentrated in their choice among antipsychotic drugs. In 2007 the single antipsychotic drug prescribed by a physician accounted for 66% of all antipsychotic prescriptions written by that physician. Which particular branded antipsychotic was the prescriber's "favorite" varied widely across physicians, i.e. physician prescribing concentration patterns are diverse. Building on Frank and Zeckhauser's [2007] characterization of physician treatments varying from "custom made" to "ready-to-wear", we construct a model of physician learning that generates a number of hypotheses. Using 2007 annual antipsychotic prescribing behavior on 17,652 physicians from IMS Health, we evaluate these predictions empirically. While physician prescribing behavior is generally quite concentrated, prescribers having greater volumes, those with training in psychiatry, male prescribers, and those not approaching retirement age tend to have less concentrated prescribing patterns.