is partially explained by the differences in their demographics. Illegal immigrants, more prevalent in the U.S. than in Canada, also add a burden to the system, as many of them do not carry health insurance and rely on emergency rooms — which are legally required to treat them under EMTALA — as a principal source of care. In Colorado, for example, an estimated 80% of undocumented immigrants do not have health insurance. The mixed system in the United States has become more similar to the Canadian system. In recent decades, managed care has become prevalent in the United States, with some 90% of privately insured Americans belonging to plans with some form of managed care. In managed care, insurance companies control patients' health care to reduce costs, for instance by demanding a second opinion prior to some expensive treatments or by denying coverage for treatments not considered worth their cost. Through all entities in its public–private system, the US spends more per capita than any other nation in the world, but is the only wealthy industrialized country in the world that lacks some form of universal healthcare. In March 2010, the US Congress passed regulatory reform of the American 'health insurance system. However, since this legislation is not fundamental healthcare reform, it is unclear what its effect will be and as the new legislation is implemented in stages, with the last provision in effect in 2018, it will be some years before any empirical evaluation of the full effects on the comparison could be determined. Healthcare costs in both countries are rising faster than inflation. As both countries consider changes to their systems, there is debate over whether resources should be added to the public or private sector. Although Canadians and Americans have each looked to the other for ways to improve their respective health care systems, there exists a substantial amount of conflicting information regarding the relative merits of the two systems. In the U.S., Canada's mostly monopsonistic health system is seen by different sides of the ideological spectrum as either a model to be followed or avoided. Medical professionals Some of the extra money spent in the United States goes to physicians, nurses, and other medical professionals. According to health data collected by the OECD, average income for physicians in the United States in 1996 was nearly twice that for physicians in Canada. In 2012, the gross average