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Propensity Score Weighting Compared to Matching in a Study of Dabigatran and Warfarin

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Abstract

Introduction

Comparing medications in observational settings requires differences in patient characteristics to be accounted for. Propensity score (PS) methods can address these differences, but PS weighting approaches may introduce bias.

Methods

Within a cohort study of anticoagulant initiators from October 2010 through to December 2012, PS values for dabigatran relative to warfarin were estimated, and study outcomes (stroke or major bleeding) among the cohort were identified. The PS was used to match initiators and results compared with those obtained using inverse probability of treatment weighting (IPTW) and standardized morbidity ratio (SMR) weighting. Hazard ratios (HRs) for study outcomes were estimated using a proportional hazards regression model.

Results

There were 23,543 dabigatran and 50,288 warfarin initiators, and matching formed 19,189 pairs (81.5% of dabigatran initiators) which resulted in a pooled stroke HR of 0.77 (95% confidence interval [CI] 0.54–1.09), and a pooled major hemorrhage HR of 0.75 (95% CI 0.65–0.87). The IPTW results for stroke (HR = 0.00; 95% CI 0.00–0.56) and major hemorrhage (HR = 0.08; 95% CI 0.08–0.10) substantially differed, while the SMR-weighted results for stroke (HR = 0.65; 95% CI 0.42–1.03) and major hemorrhage (HR = 0.73; 95% CI 0.61–0.85) differed only slightly from matching.

Conclusions

In this example, different applications of the same PS led to substantially different results, a finding that was particularly apparent with IPTW, and this was remedied by truncating extreme weights. If IPTW is used, information regarding the weights applied along with sensitivity analyses could avoid misrepresentation of study results, and would enhance their interpretation.

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Acknowledgements

The useful comments provided by Kristina Zint, PharmD of Boehringer Ingelheim are acknowledged.

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Authors and Affiliations

  1. Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, 1620 Tremont Street, Suite 3030, Boston, MA, 02120, USA

    John D. Seeger, Katsiaryna Bykov, Krista Huybrechts & Sebastian Schneeweiss

  2. Optum Epidemiology, 1325 Boylston St., Boston, MA, 02215, USA

    John D. Seeger

  3. Corporate Department Global Epidemiology, Boehringer Ingelheim GmbH, Ingelheim, Germany

    Dorothee B. Bartels

  4. Hannover Medical School, Institute for Epidemiology, Social Medicine and Health Systems Research, Hannover, Germany

    Dorothee B. Bartels

Authors
  1. John D. Seeger
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  2. Katsiaryna Bykov
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  3. Dorothee B. Bartels
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  4. Krista Huybrechts
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  5. Sebastian Schneeweiss
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Corresponding author

Correspondence to John D. Seeger.

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Funding

This research was supported by a research contract with Boehringer-Ingelheim. The research contract granted Brigham & Women’s Hospital the right to publication of the results.

Conflict of interest

John Seeger, Kate Bykov, Krista Huybrechts, and Sebastian Schneeweiss received funding support through the research contract with Boehringer-Ingelheim. Dorothee Bartels is an employee of Boehringer-Ingelheim, the manufacturer of dabigatran.

Ethical Approval

Patient data were de-identified and the study was approved by the Brigham and Women’s Hospital institutional review board.

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Seeger, J.D., Bykov, K., Bartels, D.B. et al. Propensity Score Weighting Compared to Matching in a Study of Dabigatran and Warfarin. Drug Saf 40, 169–181 (2017). https://doi.org/10.1007/s40264-016-0480-3

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