Incident User Cohorts for Assessing Medication Cost-Offsets
Article first published online: 14 MAR 2014
© Health Research and Educational Trust
Health Services Research
Volume 49, Issue 4, pages 1364–1386, August 2014
How to Cite
Stuart, B., Loh, F. E., Roberto, P. and Miller, L. (2014), Incident User Cohorts for Assessing Medication Cost-Offsets. Health Services Research, 49: 1364–1386. doi: 10.1111/1475-6773.12170
- Issue published online: 23 JUL 2014
- Article first published online: 14 MAR 2014
- Drug initiator design;
To develop and test incident drug user designs for assessing cost savings from statin use in diabetics.
Random 5 percent sample of Medicare beneficiaries, 2006–2008.
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.
Data Collection/Extraction 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.
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.
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.