More than half of commercial HMOs in the U.S. have now implemented some form of pay for performance program, according to a new study conducted by researchers at the Harvard School of Public Health. The study, which surveyed 242 commercial HMOs, concluded that 52.1 percent of the plans were using some type of pay for performance scheme. These plans collectively manage for 81.3 percent of all U.S. commercial HMO enrollees, according to the study results, which are being published today in the New England Journal of Medicine. Researchers found that nearly all (90 percent) had physician pay for performance programs in place, but only 38 percent had hospital P4P programs underway. Physician programs typically focused on clinical quality, particularly preventive care measures. Also, the HMOs tended to reward the top performing groups rather than the most improved providers.