Confronting “confounding by health system use” in Medicare Part D: comparative effectiveness of propensity score approaches to confounding adjustment
Article first published online: 3 MAY 2012
Copyright © 2012 John Wiley & Sons, Ltd.
Pharmacoepidemiology and Drug Safety
Supplement: Methods for Developing and Analyzing Clinically Rich Data for Patient-Centered Outcomes Research
Volume 21, Issue Supplement S2, pages 90–98, May 2012
How to Cite
Polinski, J. M., Schneeweiss, S., Glynn, R. J., Lii, J. and Rassen, J. A. (2012), Confronting “confounding by health system use” in Medicare Part D: comparative effectiveness of propensity score approaches to confounding adjustment. Pharmacoepidem. Drug Safe., 21: 90–98. doi: 10.1002/pds.3250
- Issue published online: 3 MAY 2012
- Article first published online: 3 MAY 2012
- Manuscript Accepted: 6 FEB 2012
- Manuscript Received: 10 AUG 2011
- Manuscript Revised: 6 FEB 2011
- National Institute on Aging. Grant Number: T32 AG000158
- National Institute of Mental Health. Grant Number: R01 5U01MH079175-02
- Agency for Healthcare Research and Quality. Grant Number: K01 HS018088
- CVS Caremark
- health service use;
- propensity score adjustment;
- high-dimensional propensity score;
- health policy
Under Medicare Part D, patient characteristics influence plan choice, which in turn influences Part D coverage gap entry. We compared predefined propensity score (PS) and high-dimensional propensity score (hdPS) approaches to address such “confounding by health system use” in assessing whether coverage gap entry is associated with cardiovascular events or death.
We followed 243,079 Medicare patients aged 65+ years with linked prescription, medical, and plan-specific data in 2005–2007. Patients reached the coverage gap and were followed until an event or year's end. Exposed patients were responsible for drug costs in the gap; unexposed patients (patients with non-Part D drug insurance and Part D patients receiving a low-income subsidy) received financial assistance. Exposed patients were 1:1 PS-matched or hdPS-matched to unexposed patients. The PS model included 52 predefined covariates; the hdPS model added 400 empirically identified covariates. Hazard ratios for death and any of five cardiovascular outcomes were compared. In sensitivity analyses, we explored residual confounding using only low-income subsidy patients in the unexposed group.
In unadjusted analyses, exposed patients had no greater hazard of death (HR = 1.00; 95%CI, 0.84–1.20) or other outcomes. PS-matched (HR = 1.29; 0.99–1.66) and hdPS-matched (HR = 1.11; 0.86–1.42) analyses showed elevated but non-significant hazards of death. In sensitivity analyses, the PS analysis showed a protective effect (HR = 0.78; 0.61–0.98), whereas the hdPS analysis (HR = 1.06; 0.82–1.37) confirmed the main hdPS findings.
Although the PS-matched analysis suggested elevated but non-significant hazards of death among patients with no financial assistance during the gap, the hdPS analysis produced lower estimates that were stable across sensitivity analyses. Copyright © 2012 John Wiley & Sons, Ltd.