I would have liked more insight into the control group (so called "matched control") hospitals. Typically, PE firms only step in when companies (in this case, hospitals) are struggling. If the PE hospitals were in dire financial straits pre-acquisition, these results don't seem too surprising.

Ideally, the control would be a set of hospitals that PE firms otherwise wanted to acquire but were blocked for reasons unrelated to financials & performance of that hospital, e.g. regulatory. Granted, I expect that might be quite rare.

To be clear, I think private equity firms have had quantifiable negative impacts in many other aspects of healthcare. For example, acquiring helicopter-rescue/air-ambulance companies and sending them out for non-emergency situations.