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The Mismeasurement of Quality by Readmission Rate: How Blunt Is too Blunt an Instrument?: A Quantitative Bias Analysis

Rumball-Smith, Juliet MBChB, MPH, PhD, FAFPHM*,†; Blakely, Tony MBChB, MPH, PhD, FAFPHM; Sarfati, Diana MBChB, MPH, FNZCPHM; Hider, Phil MBChB, MPH, FAFPHM

doi: 10.1097/MLR.0b013e31828d1275
Original Article

Background: The rate of readmission is widely used as a measure of hospital quality of care, often with funding implications for outlying facilities.

Objectives: This study explored the plausibility of readmission as a proxy for health care quality with quantitative bias analysis and the application of a structural Directed Acyclic Graph framework. It applies this paradigm to observed ethnic differences in the odds of readmission in a sample of New Zealand hospital patients.

Research Design: Ethnicity was defined as the exposure, readmission rate as the proxy outcome, and quality of care as a missing mediator. Using data from 89,090 surgical patients from New Zealand, and estimates from the literature of the prevalence of “poor quality” and the strength of the quality-of-care readmission association, a series of sensitivity analyses were performed to calculate an odds ratio of the ethnicity-readmission association corrected for the missing mediator “quality.”

Results: Given the assumptions applied, potentially only 29% of the excess odds of readmission for Māori compared with Europeans were due to poor quality of care.

Conclusions: This investigation finds substantial error when using readmission as a marker of quality, and suggests that differences in readmission between populations are more likely to be due to factors other than quality of care.

*Institute for Health and Social Policy, University of McGill, Montreal, QC, Canada

Department of Public Health & General Practice, University of Otago, Christchurch

Department of Public Health, University of Otago, Wellington, New Zealand

This work was supported by a Clinical Research Training Fellowship from the Health Research Council of New Zealand.

The authors declare no conflict of interest.

Reprints: Juliet Rumball-Smith, MBChB, MPH, PhD, FAFPHM, Institute for Health and Social Policy, University of McGill, 1130 Pine Avenue West, Montreal, QC, Canada H3A 1A3. E-mail: jrs@otagoalumni.ac.nz.

© 2013 Lippincott Williams & Wilkins, Inc.