Indeed, they write, "Critics of physician-owned hospitals -- mostly non-physician owned hospitals -- argue that physician ownership creates financial conflicts of interest, because of the concern that physician owners would have both the means and motivation to refer patients to their hospitals for unwarranted care. They would then have the opportunity to make money both from the care they provide and from any profits their hospitals realize (so-called 'double dipping'). The reality is that such "double dipping" can occur in large integrated healthcare delivery systems that own physician groups. This set up allows for it. For example, Optum, a subsidiary of the insurer UnitedHealth Group, is affiliated with 70,000 physicians, making it the largest employer of physicians in the U.S. These health systems are not subject to self-referral restrictions and can even mandate that contracted physicians refer patients to their hospitals."