214913 Use of Instrumental Variable in Prescription Drug Research with Observational Data: A Systematic Review

Tuesday, November 9, 2010 : 12:35 PM - 12:55 PM

Yong Chen, MD, MHS , Clinical and Population Health, University of Massachusetts Medical School, Worcester, MA
Becky Briesacher, PhD , Geriatric Medicine, University of Massachusetts Medical School, Worcester, MA
Objective: Instrumental variable (IV) analysis may be useful approach for addressing unmeasured confounding bias in observational studies of prescription drugs by substituting actual exposure with IVs that are: 1) strongly related to treatment assignment; and yet 2) uncorrelated with factors predicting outcome (key assumptions). Study Design and Methods: We conducted a systematic review assessing the use of IV methods, summarizing major types of IVs and evaluating evidence for assumptions. We searched MEDLINE, OVID, PsychoInfo, Econlit and economic databases from 1961 to 2009. Results: We identified 26 studies. Most (n=16) were published after 2007. We identified five major types of IVs: regional variation (n=8), facility prescribing patterns (n=5), physician preference (n=8), patient history/financial status (n=3) and calendar time (n=4). Evidence supporting the validity of IV was inconsistent. All studies addressed the first assumption; however, there was no standard for reporting evidence that IV sufficiently predicted treatment assignment. For the second assumption, 23 studies provided explicit argument that IV was uncorrelated with factors predicting outcome, and 18 supported argument with empirical evidence. Conclusions: Use of IV methods is increasing in prescription drug research. However, we did not find evidence of a dominant IV. Future research should develop standards for identifying IVs and reporting performance on key assumptions.

Learning Areas:
Biostatistics, economics

Learning Objectives:
Briefly introduce instrumental variable (IV) approach that addresses unmeasured confounding bias in observational studies. Evaluate use of IV approach in prescription drug research with observational data in the existing literature. Summarize five types of IVs that have been applied to prescription drug research.

Keywords: Outcomes Research, Methodology

Presenting author's disclosure statement:

Qualified on the content I am responsible for because: I am qualified to present because I conduct the review.
Any relevant financial relationships? No

I agree to comply with the American Public Health Association Conflict of Interest and Commercial Support Guidelines, and to disclose to the participants any off-label or experimental uses of a commercial product or service discussed in my presentation.