“…5 Many of the problems of poor care coordination result either from mishandled referrals to specialists (Mehrotra, Forrest, and Lin, 2011) or from fragmented care delivery (see Cebul et al, 2008;and Rebitzer and Votruba, 2011, for a discussion of the problem of care fragmentation and Frandsen et al, 2015;Hussey et al, 2014;Agha, Frandsen, and Rebitzer, 2017;and Romano, Segal, and Pollack, 2015, for estimates of its costs). 6 Mishandled referrals and fragmented care delivery are exacerbated by relatively weak investments in technology and process improvements that strengthen integration across providers and organizations (Milstein and Gilbertson, 2009;Simon et al, 2017). 7 Medical care in the United States has been historically delivered by practitioners operating out of their own offices or as attendings in hospitals (Starr, 1984;Robinson, 1999), and although it still commonly is (Burns, Goldsmith, and Sen, 2013;Baker, Bundorf, and Royalty, 2014), a rapidly growing percentage of physicians are operating in large groups organized by nonphysician owners (see Burns and Pauly, 2018, for a review of physician models of practice organization).…”