EXHIBIT 3.

Changes in Organizational Structure from the pre-ACA to post-ACA period by 2014 ACO Program Participation

	Did not enter ACO programs by 2014		Entered ACO programs by 2014
Physician- or Practice-level (TIN) Characteristics	Pre-Period (2008–2010)	Post-Period (2011–2013)	Pre-Period (2008–2010)	Post-Period (2011–2013)	Differential Change for ACO Program Participants
Practice in a hospital-owned facility, percent of physicians	16.9%	19.3%	20.2%	23.7%	1.1%
Practice acquired, percent of physicians	0.1%	0.2%	0.4%	0.3%	−0.02%
Physicians’ mean practice (TIN) size, number of physicians	69.3	77.2	130.6	149.9	11.4**

SOURCE Authors’ analysis of data from the Centers for Medicare and Medicaid and Irving Levin Associates.

NOTES Each line results from separate within-market analyses, presenting the average pre- and post-period value of the dependent variable, by 2012, 2013, or 2014 ACO participation. Physician’s mean practice size was calculated as the average count of physician billing for outpatient care within a TIN, weighting each TIN by its share of total physicians in the MSA. Percent of physicians acquired was calculated as the share of physicians billing under a TIN that was identified as the target of a merger or acquisition in any given year. ACO is Accountable Care Organization. TIN is tax identification number

^**p<0.05