Seventeen studies (number of participants unclear) were included in the review: 9 randomised controlled trials, 4 controlled trials with before-and-after data and 4 cross-sectional surveys.
Six studies were assigned a quality grade of 3, six were assigned a grade of 2, and five were assigned a grade of 1.
Of the 2 studies that evaluated financial incentives provided at the payment-system level, one found a positive effect on access to care while the other found a negative effect on access to care for the sickest patients.
Of the 9 studies that evaluated the use of financial incentives directed to provider groups, two reported improvements for all quality of care measures, five were classified as partial improvement studies, and two showed no effect of the intervention compared with the control group.
Of the 6 studies that evaluated the effects of financial incentives at the physician level, two reported a positive effect of the intervention and three reported some positive effects (partial studies).
Five studies found unintended effects of the incentive, including an unintended incentive to avoid the most severely ill patients (1 study), 'gaming behaviour', i.e. exaggerating the initial health status of the patients (1 study), and improvements in documentation rather than actual changes in the quality of health care (3 studies).
Two studies reported that individuals or groups with the lowest baseline performance improved the most; however, if threshold performance targets are used, they may gain the least performance pay (1 study).