title: Effects of increased patient cost sharing on socioeconomic disparities in health care.
abstract: BACKGROUND
  Increasing patient cost sharing is a commonly employed mechanism to contain health care expenditures.
  
  
  OBJECTIVE
  To explore whether the impact of increases in prescription drug copayments differs between high- and low-income areas.
  
  
  METHODS
  Using a database of 6 million enrollees with employer-sponsored health insurance, econometric models were used to examine the relationship between changes in drug copayments and adherence with medications for the treatment of diabetes mellitus (DM) and congestive heart failure (CHF).
  
  
  METHODS
  Individuals 18 years of age and older meeting prespecified diagnostic criteria for DM or CHF were included.
  
  
  METHODS
  Median household income in the patient's ZIP code of residence from the 2000 Census was used as the measure of income. Adherence was measured by medication possession ratio: the proportion of days on which a patient had a medication available.
  
  
  RESULTS
  Patients in low-income areas were more sensitive to copayment changes than patients in high- or middle-income areas. The relationship between income and price sensitivity was particularly strong for CHF patients. Above the lowest income category, price responsiveness to copayment rates was not consistently related to income.
  
  
  CONCLUSIONS
  The relationship between medication adherence and income may account for a portion of the observed disparities in health across socioeconomic groups. Rising copayments may worsen disparities and adversely affect health, particularly among patients living in low-income areas.
authors.affiliation: Department of Health Care Policy, Harvard Medical School, Boston, MA 02115, USA. chernew@hcp.med.harvard.edu
authors.forename: Michael
authors.initials: M
authors.lastname: Chernew
authors.forename: Teresa B
authors.initials: TB
authors.lastname: Gibson
authors.forename: Kristina
authors.initials: K
authors.lastname: Yu-Isenberg
authors.forename: Michael C
authors.initials: MC
authors.lastname: Sokol
authors.forename: Allison B
authors.initials: AB
authors.lastname: Rosen
authors.forename: A Mark
authors.initials: AM
authors.lastname: Fendrick
mesh_terms: D015897:Comorbidity; D017047:Cost Sharing / Q000191:economics*; D003920:Diabetes Mellitus / Q000188:drug therapy*; D016527:Drug Costs; D011307:Drug Prescriptions / Q000191:economics*; D005252:Fees, Pharmaceutical; D005260:Female; D005102:Health Expenditures; D054624:Health Status Disparities; D006333:Heart Failure / Q000188:drug therapy*; D006801:Humans; D007182:Income / Q000706:statistics & numerical data; D016014:Linear Models; D008297:Male; D055118:Medication Adherence; D014481:United States