Racial bias in health algorithms

The U.S. health care system uses commercial algorithms to guide health decisions. Obermeyer et al. find evidence of racial bias in one widely used algorithm, such that Black patients assigned the same level of risk by the algorithm are sicker than White patients (see the Perspective by Benjamin). The authors estimated that this racial bias reduces the number of Black patients identified for extra care by more than half. Bias occurs because the algorithm uses health costs as a proxy for health needs. Less money is spent on Black patients who have the same level of need, and the algorithm thus falsely concludes that Black patients are healthier than equally sick White patients. Reformulating the algorithm so that it no longer uses costs as a proxy for needs eliminates the racial bias in predicting who needs extra care.
Science, this issue p. 447; see also p. 421


Health systems rely on commercial prediction algorithms to identify and help patients with complex health needs. We show that a widely used algorithm, typical of this industry-wide approach and affecting millions of patients, exhibits significant racial bias: At a given risk score, Black patients are considerably sicker than White patients, as evidenced by signs of uncontrolled illnesses. Remedying this disparity would increase the percentage of Black patients receiving additional help from 17.7 to 46.5%. The bias arises because the algorithm predicts health care costs rather than illness, but unequal access to care means that we spend less money caring for Black patients than for White patients. Thus, despite health care cost appearing to be an effective proxy for health by some measures of predictive accuracy, large racial biases arise. We suggest that the choice of convenient, seemingly effective proxies for ground truth can be an important source of algorithmic bias in many contexts.

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Supplementary Material


Materials and Methods
Figs. S1 to S5
Tables S1 to S4
References (4651)


File (aax2342_obermeyer_sm.pdf)

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Information & Authors


Published In

Volume 366 | Issue 6464
25 October 2019

Submission history

Received: 8 March 2019
Accepted: 4 October 2019
Published in print: 25 October 2019


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We thank S. Lakhtakia, Z. Li, K. Lin, and R. Mahadeshwar for research assistance and D. Buefort and E. Maher for data science expertise. Funding: This work was supported by a grant from the National Institute for Health Care Management Foundation. Author contributions: Z.O. and S.M. designed the study, obtained funding, and conducted the analyses. All authors contributed to reviewing findings and writing the manuscript. Competing interests: The analysis was completely independent: None of the authors had any contact with the algorithm’s manufacturer until after it was complete. No authors received compensation, in any form, from the manufacturer or have any commercial interests in the manufacturer or competing entities or products. There were no confidentiality agreements that limited reporting of the work or its results, no material transfer agreements, no oversight in the preparation of this article (besides ethical oversight from the approving IRB, which was based at a non-profit academic health system), and no formal relationship of any kind between any of the authors and the manufacturer. Data and materials availability: Because the data used in this analysis are protected health information, they cannot be made publicly available. We provide instead a synthetic dataset (using the R package synthpop) and all code necessary to reproduce our analyses at



School of Public Health, University of California, Berkeley, Berkeley, CA, USA.
Department of Emergency Medicine, Brigham and Women’s Hospital, Boston, MA, USA.
Brian Powers
Department of Medicine, Brigham and Women’s Hospital, Boston, MA, USA.
Christine Vogeli
Mongan Institute Health Policy Center, Massachusetts General Hospital, Boston, MA, USA.
Booth School of Business, University of Chicago, Chicago, IL, USA.

Funding Information

National Institute for Health Care Management Foundation


These authors contributed equally to this work.
†Corresponding author. Email: [email protected]

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