title: Measures of adherence to oral hypoglycemic agents at the primary care clinic level: the role of risk adjustment.
abstract: BACKGROUND
  Prior research found that in the Veterans Affairs health care system (VA), the proportion of patients adherent to oral hypoglycemic agents varies from 50% to 80% across primary care clinics. This study examined whether variation in patient and facility characteristics determined those differences.
  
  
  METHODS
  Retrospective cohort study of 444,418 VA primary care patients with diabetes treated in 559 clinics in fiscal year (FY) 2006-2007. Patients' adherence to each oral hypoglycemic agent was computed for the first 3 months of FY2007, and averaged across agents to produce an adherence score for the patient's overall regimen. Patients with an adherence score over 0.8 were defined as adherent. Risk adjustment used hierarchical logistic regression accounting for patient factors and facility effects by clustering patients within clinics and clinics within parent VA medical centers. We then assessed the influence of risk adjustment using observed-to-expected (O/E) ratios computed for each clinic.
  
  
  RESULTS
  The mean unadjusted proportion of adherent patients in clinics was 0.715 (interdecile range 0.559-0.826). The percent variation in patient's likelihood of being adherent explained at the patient, clinic, and parent VA medical center levels was 2.94%, 0.27%, and 0.76%, respectively. The mean clinic-level observed-to-expected ratio was 1.001 (interdecile range 0.975-1.027).
  
  
  CONCLUSIONS
  The variation in the proportion of patients adherent across clinics remained large after risk adjustment. As patient and facility effects explained only 4% of the variance in adherence, comparing clinics based on unadjusted scores is a reasonable starting point unless more predictive patient, provider, and facility factors are identified.
authors.affiliation: Northwest Center for Outcomes Research in Older Adults, VA Puget Sound Health Care System, WA 98101, USA. eswong@uw.edu
authors.forename: Edwin S
authors.initials: ES
authors.lastname: Wong
authors.forename: John D
authors.initials: JD
authors.lastname: Piette
authors.forename: Chuan-Fen
authors.initials: CF
authors.lastname: Liu
authors.forename: Mark
authors.initials: M
authors.lastname: Perkins
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Maciejewski
authors.forename: George L
authors.initials: GL
authors.lastname: Jackson
authors.forename: David K
authors.initials: DK
authors.lastname: Blough
authors.forename: Stephan D
authors.initials: SD
authors.lastname: Fihn
authors.forename: David H
authors.initials: DH
authors.lastname: Au
authors.forename: Chris L
authors.initials: CL
authors.lastname: Bryson
mesh_terms: D000284:Administration, Oral; D000367:Age Factors; D000368:Aged; D000554:Ambulatory Care Facilities / Q000706:statistics & numerical data*; D003920:Diabetes Mellitus / Q000188:drug therapy*; D005260:Female; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage* / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D011320:Primary Health Care / Q000706:statistics & numerical data*; D012189:Retrospective Studies; D020379:Risk Adjustment; D012737:Sex Factors; D012959:Socioeconomic Factors; D014481:United States; D014493:United States Department of Veterans Affairs / Q000706:statistics & numerical data; D016903:Drug Monitoring
chemical_list: D007004:Hypoglycemic Agents