This work has been presented at the 27th International Conference on Pharmacoepidemiology and Therapeutic Risk Management, Chicago, IL, 2011 (“Calendar Time-Specific Propensity Scores and Hazard Ratio Estimation”), and the 44th Annual Meeting, Society for Epidemiologic Research, Montreal, Canada, 2011 (“Time-Varying Propensity Scores and Hazard Ratio Estimation”).
Calendar time-specific propensity scores and comparative effectiveness research for stage III colon cancer chemotherapy†
Version of Record online: 7 JAN 2013
Copyright © 2013 John Wiley & Sons, Ltd.
Pharmacoepidemiology and Drug Safety
Volume 22, Issue 8, pages 810–818, August 2013
How to Cite
Mack, C. D., Glynn, R. J., Brookhart, M. A., Carpenter, W. R., Meyer, A. M., Sandler, R. S. and Stürmer, T. (2013), Calendar time-specific propensity scores and comparative effectiveness research for stage III colon cancer chemotherapy. Pharmacoepidem. Drug Safe., 22: 810–818. doi: 10.1002/pds.3386
- Issue online: 21 JUL 2013
- Version of Record online: 7 JAN 2013
- Manuscript Accepted: 9 NOV 2012
- Manuscript Revised: 6 NOV 2012
- Manuscript Received: 8 AUG 2012
- National Institute on Aging. Grant Number: R01 AG023178
- National Cancer Institute. Grant Number: R01 CA124402
- propensity scores;
- epidemiologic methods;
- comparative effectiveness research;
- colon cancer;
Nonexperimental studies of treatment effectiveness provide an important complement to randomized trials by including heterogeneous populations. Propensity scores (PSs) are common in these studies but may not adequately capture changes in channeling experienced by innovative treatments. We use calendar time-specific (CTS) PSs to examine the effect of oxaliplatin during dissemination from off-label to widespread use.
Stage III colon cancer patients aged 65+ years initiating chemotherapy between 2003 and 2006 were examined using cancer registry data linked with Medicare claims. Two PS approaches for receipt of oxaliplatin versus 5-flourouricil were constructed using logistic models with key components of age, sex, substage, grade, census-level income, and comorbidities: (i) a conventional, year-adjusted PS and (ii) a CTS PS constructed and matched separately within 1-year intervals, then combined. We compared PS-matched hazard ratios (HRs) for mortality using Cox models.
Oxaliplatin use increased significantly; 8% (n = 86) of patients received it in the first time period versus 52% (n = 386) in the last. Channeling by comorbidities, income, and age appeared to change over time. The CTS PS improved covariate balance within calendar time strata and yielded an attenuated estimated benefit of oxaliplatin (HR = 0.75) compared with the conventional PS (HR = 0.69).
In settings where prescribing patterns have changed and calendar time acts as a confounder, a CTS PS can characterize changes in treatment choices and estimating separate PSs within specific calendar time periods may result in enhanced confounding control. To increase validity of comparative effectiveness research, researchers should carefully consider drug lifecycles and effects of innovative treatment dissemination over time. Copyright © 2013 John Wiley & Sons, Ltd.