title: Incident user cohorts for assessing medication cost-offsets.
abstract: OBJECTIVE
  To develop and test incident drug user designs for assessing cost savings from statin use in diabetics.
  
  
  METHODS
  Random 5 percent sample of Medicare beneficiaries, 2006-2008.
  
  
  METHODS
  Seven-step incident user design to assess impact of statin initiation on subsequent Medicare spending: (1) unadjusted pre/post initiation test; (2) unadjusted difference-in-difference (DID) with comparison series; (3) adjusted DID; (4) propensity score (PS)-matched DID with static and dynamic baseline covariates; (5) PS-matched DID by drug adherence strata; (6) PS-matched DID for high adherers controlling for healthy adherer bias; and (7) replication for ACE-inhibitor/ARB initiators.
  
  
  METHODS
  Subjects with prevalent diabetes and no statin use (January-June 2006) and statin initiation (July 2006-January 2008) compared to nonusers with a random "potential-initiation" month. Monthly Medicare spending tracked 24 months pre- and post-initiation.
  
  
  RESULTS
  Statistically significant savings in Medicare spending were observed beginning 7 months post-initiation for statins and 13 months post-initiation for ACEIs/ARBs. However, these savings were only observed for adherent patients in steps 5 and 6.
  
  
  CONCLUSIONS
  Drug initiator designs are more robust to confounding than prevalent user designs in assessing cost-offsets from drug use but still require other adjustments and sensitivity analysis to ensure proper inference.
authors.affiliation: Peter Lamy Center on Drug Therapy and Aging, Department of Pharmaceutical Health Services Research, University of Maryland School of Pharmacy, 220 Arch Street, Room 12-212, Baltimore, MD 21201.
authors.forename: Bruce
authors.initials: B
authors.lastname: Stuart
authors.forename: F Ellen
authors.initials: FE
authors.lastname: Loh
authors.forename: Pamela
authors.initials: P
authors.lastname: Roberto
authors.forename: Laura
authors.initials: L
authors.lastname: Miller
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D057186:Comparative Effectiveness Research; D017046:Cost Savings; D016208:Databases, Factual; D003920:Diabetes Mellitus; D005260:Female; D006801:Humans; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000191:economics* / Q000627:therapeutic use; D008297:Male; D016344:Medicare Part A / Q000191:economics; D016345:Medicare Part B / Q000191:economics; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D057216:Propensity Score; D012107:Research Design; D014481:United States
chemical_list: D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors
keywords: Drug initiator design; cost-offsets; statins