From MONETIZING MEDICINE: PRIVATE EQUITY AND COMPETITION IN PHYSICIAN PRACTICE MARKETS, a report by the American Antitrust Institute:
Price increases associated with PE acquisitions are exceptionally high where a PE firm controls a competitively significant share of the local market. When we focus our analysis on markets where a single PE firm controls more than 30% of the market, we find further elevated prices associated with PE acquisitions in each of the 3 specialties with statistically significant results, for gastroenterology (18%), obstetrics and gynecology (16%), and dermatology (13%).
Discussed in the NYTimes here.