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American Journal of Epidemiology Advance Access originally published online on May 17, 2006
American Journal of Epidemiology 2006 164(3):272-281; doi:10.1093/aje/kwj180
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American Journal of Epidemiology Copyright © 2006 by the Johns Hopkins Bloomberg School of Public Health All rights reserved; printed in U.S.A.

Practice of Epidemiology

Measuring Screening Intensity in Case-Control Studies of the Efficacy of Mammography

A. Russell Localio1, Lan Zhou1,2 and Sandra A. Norman1

1 Department of Biostatistics and Epidemiology, Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, Philadelphia, PA
2 Department of Statistics, College of Science, Texas A&M University, College Station, TX

Correspondence to Dr. A. Russell Localio, 606 Blockley Hall, 423 Guardian Drive, University of Pennsylvania, Philadelphia, PA 19104-6021 (e-mail: rlocalio{at}cceb.med.upenn.edu).

Of great interest in studies of screening for breast cancer is the relative efficacy of different screening frequencies (intensities). Prior work has suggested that estimates of the association between screening intensity and outcome in case-control studies would not produce valid results and that only binary indicators (no screens vs. one or more) of exposure can be used. Using case-control studies drawn from simulated cohorts of 30,000–40,000 women, the authors found that biases demonstrated in prior studies can be explained by 1) misclassification of true exposure groups by observed screening history, and 2) differential exposure misclassification of cases and controls. Binary as well as ordered categorical and interval measures can be biased unless they account for misclassification. By combining measurements of screening history from multiple periods of observation of varying lengths and using repeated-measures logistic regression models, the effect of screening intensity can be estimated in the presence of misclassification. Assessing the effect of screening intensity in case-control studies of mammography is possible if principles and methods for misclassification and measurement error guide the analysis.

bias (epidemiology); case-control studies; computer simulation; mammography

Abbreviations: DPP, detectable preclinical phase; REW, retrospective exposure window


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