Socioeconomic position and health among persons with diabetes mellitus: a conceptual framework and review of the literature. - Brown,A.; Ettner,S.; Piette,J.; Weinberger,M.; Gregg,E.; Shapiro,M.; Karter,A.; Safford,M.; Waitzfelder,B.; Prata,P.; Beckles,G. (Epidemiol Rev, 2004)