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Appears in Collections:Faculty of Health Sciences and Sport Journal Articles
Peer Review Status: Refereed
Title: Drug exposure risk windows and unexposed comparator groups for cohort studies in pharmacoepidemiology
Author(s): McMahon, Alex
Evans, Josie
McGilchrist, Mark M
McDevitt, Denis G
MacDonald, Thomas M
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Keywords: Cohort study
Risk window
Unexposed group
Issue Date: Aug-1998
Date Deposited: 3-Sep-2012
Citation: McMahon A, Evans J, McGilchrist MM, McDevitt DG & MacDonald TM (1998) Drug exposure risk windows and unexposed comparator groups for cohort studies in pharmacoepidemiology. Pharmacoepidemiology and Drug Safety, 7 (4), pp. 275-280.;2-N/abstract
Abstract: Aim: To determine the appropriate size of risk windows in both exposed and unexposed sub-cohorts. Method: Data was taken from a previous study of upper gastrointestinal haemorrhage and perforation. The length of each prescription for NSAIDs was estimated. The risk was calculated for the duration of a prescription plus increments of -30, -25, ..., +115, +120 (i.e. 31 increments). Ten unexposed groups were re-sampled for each increment (stratified for age and sex), using the same lengths of risk window as the exposed group. Mean risks and rate-ratios were calculated (per thousand person-years). Results: The NSAID risk rose from 3·52 at -30 days to a peak of 5·82 at -15 days, and then decreased gradually to 2·83 at +120 days. Unexposed risk was variable for the negative increments, and decreased gradually from 2·16 at +0 days to 1·54 at +120 days. The rate-ratio rose from 1·55 at -30 days to a peak of 2·85 at -5 days, and then decreased to 1·85 at +120 days. Conclusion: Risk windows should be the same as (or slightly less than) the calculated length of a prescription. Lengthy windows should not be used for unexposed comparator groups (the exposed windows may be randomly allocated).
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