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IJE Advance Access originally published online on August 26, 2006
International Journal of Epidemiology 2006 35(6):1442-1446; doi:10.1093/ije/dyl176
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Published by Oxford University Press on behalf of the International Epidemiological Association © The Author 2006; all rights reserved.

Article

Combined analysis of retrospective and prospective occurrences in cohort studies: HIV-1 serostatus and incident pneumonia

Stephen R Cole1,*, Haitao Chu1, Paul D Allison2 and Stephen J Gange1

1 Department of Epidemiology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA.
2 Department of Sociology, University of Pennsylvania, PA, USA.

* Corresponding author. Department of Epidemiology, Johns Hopkins University Bloomberg School of Public Health, 615 North Wolfe Street, Room E7640, Baltimore, MD 21205 USA. E-mail: scole{at}jhsph.edu


  Abstract

Background The authors show how information collected on retrospective occurrence times may be combined with prospective occurrence times in the analysis of recurrent events from cohort studies.

Methods We demonstrate how the observed data can be expanded from one to two records per participant and account for the within-individual dependence when estimating variances. We illustrate our methods using data from the Women's Interagency HIV Study, which recorded 384 retrospective and 352 prospective occurrences of pneumonia in 9478 retrospective and 7857 prospective person-years among 2610 adult women.

Results The hazard of non-Pneumocystis carinii pneumonia among the 2056 HIV-1 infected women was 2.24 times (95% confidence limits: 1.74, 2.89) that of the 554 uninfected women, independent of age. This hazard ratio was homogeneous across retrospective and prospective occurrences (P for interaction = 0.96) and combining occurrence types increased the precision by reducing the standard error by about a fourth.

Conclusions As expected, HIV-1 infection increases the hazard of pneumonia, with more precise inference obtained by combining information available on bidirectional occurrences. The proposed method for the analysis of bidirectional occurrence times will improve precision when the estimated associations are homogeneous across occurrence types, or may provide added insight into either the data collection or disease process when the estimated associations are heterogeneous.

Keywords Cohort studies, HIV-1, survival analysis, recurrent events

Accepted 7 July 2006


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