Gender homophily in referral networks: Consequences for the medicare physician earnings

I assess the extent to which the gender gap in physician earnings may be driven by physicians' preference for referring to specialists of the same gender. Analyzing administrative data on 100 million Medicare patient referrals, I provide robust evidence that doctors refer more to specialists of their own gender. I show that biased referrals are predominantly driven by physicians' decisions rather than by endogenous sorting of physicians or patients. Because most referring doctors are male, the net impact of same-gender bias by both male and female doctors generates lower demand for female relative to male specialists, pointing to a positive externality for increased female participation in medicine.