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Biostatistics Advance Access originally published online on June 10, 2008
Biostatistics 2009 10(1):70-79; doi:10.1093/biostatistics/kxn016
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© The Author 2008. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org.

Combining data from 2 nested case–control studies of overlapping cohorts to improve efficiency

Agus Salim*

Department of Community, Occupational and Family Medicine, Yong Loo Lin School of Medicine, National University of Singapore and Centre for Mental Health Research, Australian National University Canberra ACT 0200, Australia

Christina Hultman, Pär Sparén and Marie Reilly

Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Box 281 SE 17177, Stockholm, Sweden cofaguss{at}nus.edu.sg

* To whom correspondence should be addressed.

Researchers subject to time and budget constraints may conduct small nested case–control studies with individually matched controls to help optimize statistical power. In this paper, we show how precision can be improved considerably by combining data from a small nested case–control study with data from a larger nested case–control study of a different outcome in the same or overlapping cohort. Our approach is based on the inverse probability weighting concept, in which the log-likelihood contribution of each individual observation is weighted by the inverse of its probability of inclusion in either study. We illustrate our approach using simulated data and an application where we combine data sets from 2 nested case–control studies to investigate risk factors for anorexia nervosa in a cohort of young women in Sweden.

Keywords: Anorexia; Cost efficiency; Matching; Proportional hazards; Weighted likelihood

Received July 23, 2007; revised March 11, 2008; revised April 7, 2008; accepted for publication May 12, 2008.


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