Background: Systematic coding systems are used to define clinically meaningful outcomes when leveraging administrative claims data for research. How and when these codes are applied within a research study can have implications for the study validity and their specificity can vary significantly depending on treatment received.
Subjects: Data are from the Surveillance, Epidemiology, and End Results-Medicare linked dataset.
Study Design: We use propensity score methods in a retrospective cohort of prostate cancer patients first examined in a recently published radiation oncology comparative effectiveness study.
Results: With the narrowly defined outcome definition, the toxicity event outcome rate ratio was 0.88 per 100 person-years (95% confidence interval, 0.71–1.08). With the broadly defined outcome, the rate ratio was comparable, with 0.89 per 100 person-years (95% confidence interval, 0.76–1.04), although individual event rates were doubled. Some evidence of surveillance bias was suggested by a higher rate of endoscopic procedures the first year of follow-up in patients who received proton therapy compared with those receiving intensity-modulated radiation treatment (11.15 vs. 8.90, respectively).
Conclusions: This study demonstrates the risk of introducing bias through subjective application of procedure codes. Careful consideration is required when using procedure codes to define outcomes in administrative data.
*Department of Epidemiology, Gillings School of Global Public Health
†Lineberger Comprehensive Cancer Center
‡Sheps Center for Health Services Research, University of North Carolina at Chapel Hill
§Department of Health Policy and Management, Gillings School of Global Public Health
∥Department of Radiation Oncology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC
Supported by the Agency for Healthcare Research and Quality, US Department of Health and Human Services as part of the DEcIDE program, contract HHSA290-2005-0040-ITO6. Work on this study was also supported by the Integrated Cancer Information and Surveillance System, UNC Lineberger Comprehensive Cancer Center, with funding provided by the University Cancer Research Fund via the state of North Carolina.
T.S. receives investigator-initiated research funding and support as Principal Investigator (R01 AG023178) from the National Institute on Aging at the National Institutes of Health. He also receives research funding as Principal Investigator of the UNC-DEcIDE center from the Agency for Healthcare Research and Quality. He does not accept personal compensation of any kind from any pharmaceutical company, although he receives salary support from the Center for Pharmacoepidemiology and from unrestricted research grants from pharmaceutical companies (GlaxoSmithKline, Merck, Sanofi) to the department of epidemiology, University of North Carolina at Chapel Hill. The remaining authors declare no conflict of interest.
Reprints: Anne-Marie Meyer, PhD, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, CB #7293, Chapel Hill, NC 27599-7293.. E-mail: email@example.com.