The Annals of Internal Medicine published a study examining the impact of financial incentives on hospitals serving higher proportions of low-income patients.  The study found that, though hospitals serving larger populations of low-income patients typically had lower quality of care scores, quality improved at those hospitals that implemented pay-for-performance financial incentives. 

Jha, A., Orav, E., and Epstein, A. (2010). The effect of financial incentives on hospitals that serve poor patients. Annals of Internal Medicine, 153(5):299-306. http://www.annals.org/content/153/5/299.abstract

Authors: Ashish K. Jha, E. John Orav, and Arnold M. Epstein