This poster was presented at ASHEcon in June, 2019, and is joint work with Samuel A. Kleiner.

This work is preliminary and incomplete. Please do not cite or reference without permission. The working paper can be found here.

Paper Punchline:

1. PCPs who join an ACO, with specialists they did not previously refer to shift their referrals towards specialists in their ACO at the expense of specialists outside their ACO.
2. PCPs who do NOT join an ACO, but previously referred a high share of specialists who join an ACO reduce the share of referrals to ACO specialists

This paper examines how primary care providers (PCPs) change their referral patterns to specialists after they join a Medicare Shared Savings Program Accountable Care Organization (ACO). We find that primary-care providers respond differently to ACO formation depending on the degree to which the providers have a pre-existing relationship with specialists in the ACO. Relatively speaking, the smaller the previous PCP-specialist relationship, the bigger the response. We also find that primary-care providers without a pre-existing relationship with ACO specialists make up a large share of the ACOs PCPs and referrals. PCPs that sent a large share of referrals to specialists that join an ACO in the years prior to ACO formation decrease the number of patient they refer to those specialists.