Get access

Calendar time-specific propensity scores and comparative effectiveness research for stage III colon cancer chemotherapy

Authors

  • Christina DeFilippo Mack,

    Corresponding author
    • Department of Epidemiology, UNC Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
    Search for more papers by this author
  • Robert J. Glynn,

    1. Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA
    Search for more papers by this author
  • M. Alan Brookhart,

    1. Department of Epidemiology, UNC Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
    Search for more papers by this author
  • William R. Carpenter,

    1. Department of Health Policy and Management, Gillings School of Global Public Health UNC, Chapel Hill, NC, USA
    2. Lineberger Comprehensive Cancer Center and Cecil G. Sheps Center for Health Services Research, University of North Carolina, Chapel Hill, NC, USA
    Search for more papers by this author
  • Anne Marie Meyer,

    1. Lineberger Comprehensive Cancer Center and Cecil G. Sheps Center for Health Services Research, University of North Carolina, Chapel Hill, NC, USA
    Search for more papers by this author
  • Robert S. Sandler,

    1. Division of Gastroenterology and Hepatology, University of North Carolina, Chapel Hill, NC, USA
    Search for more papers by this author
  • Til Stürmer‎

    1. Department of Epidemiology, UNC Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
    Search for more papers by this author

  • 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”).

Correspondence to: C.D. Mack, University of North Carolina at Chapel Hill, 2101 McGavran-Greenberg Hall, CB #7435, Chapel Hill, NC 27599-7435, USA. E-mail: cdmack@unc.edu

ABSTRACT

Purpose

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.

Methods

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.

Results

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).

Conclusion

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.

Ancillary