Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

A Possible Overestimation of the Effect of Aspirin

A Possible Overestimation of the Effect of Aspirin In their nested case-control study on aspirin use and mortality in women within the Nurses Health Study, Chan et al1 conclude that aspirin use is associated with a decreased mortality. The reported effect is clearly stronger than results of previous randomized controlled trials suggested. The effect of aspirin in this study may be overestimated for 2 reasons that are remediable. The comparison between women taking aspirin and women not taking aspirin may not be straightforward for reasons other than the known difference in risk factors between these groups. Women taking aspirin regularly for preventive reasons may have a healthier lifestyle and may be more compliant users of medications, factors that are known to lead to too optimistic estimates of effects.2 It would therefore be interesting to evaluate the effect of aspirin on all-cause as well as cardiovascular- and malignancy-related mortality in patients taking aspirin for chronic headaches or musculoskeletal pain. In this subgroup, the use of aspirin is a necessity dictated by pain, which leads to regular intake, and its use is not related to a desire for general cardiovascular prevention among health-conscious persons. Because in this subgroup the reason for aspirin exposure was not related to the outcome of interest, the effect of aspirin may be more properly estimated. Furthermore, the method that was used for selecting control subjects may give rise to an overestimation of the effect of aspirin. Control subjects were all the participants who did not become a case subject (ie, who did not die) during follow-up in this closed cohort study, which is known to increasingly overestimate odds ratios when the disease incidence is larger than 5% to 10%.3,4 The mortality in the study by Chan et al1 was 12%. A simple approximate method to correct this bias can be used.5 Correspondence: Mr Snoep, Department of Clinical Epidemiology, C9-P, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, the Netherlands (J.D.Snoep@lumc.nl). References 1. Chan ATManson JEFeskanich DStampfer MJColditz GAFuchs CS Long-term aspirin use and mortality in women. Arch Intern Med 2007;167 (6) 562- 572PubMedGoogle ScholarCrossref 2. Baron JA Can aspirin keep mortality at bay? Arch Intern Med 2007;167 (6) 535- 536PubMedGoogle ScholarCrossref 3. Greenland SThomas DC On the need for the rare disease assumption in case-control studies. Am J Epidemiol 1982;116 (3) 547- 553PubMedGoogle Scholar 4. Lubin JHGail MH Biased selection of controls for case-control analyses of cohort studies. Biometrics 1984;40 (1) 63- 75PubMedGoogle ScholarCrossref 5. Zhang JYu KF What's the relative risk? a method of correcting the odds ratio in cohort studies of common outcomes. JAMA 1998;280 (19) 1690- 1691PubMedGoogle ScholarCrossref http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Internal Medicine American Medical Association

A Possible Overestimation of the Effect of Aspirin

Loading next page...
 
/lp/american-medical-association/a-possible-overestimation-of-the-effect-of-aspirin-MBDjorbp07
Publisher
American Medical Association
Copyright
Copyright © 2007 American Medical Association. All Rights Reserved.
ISSN
0003-9926
DOI
10.1001/archinte.167.21.2372-b
pmid
18040005
Publisher site
See Article on Publisher Site

Abstract

In their nested case-control study on aspirin use and mortality in women within the Nurses Health Study, Chan et al1 conclude that aspirin use is associated with a decreased mortality. The reported effect is clearly stronger than results of previous randomized controlled trials suggested. The effect of aspirin in this study may be overestimated for 2 reasons that are remediable. The comparison between women taking aspirin and women not taking aspirin may not be straightforward for reasons other than the known difference in risk factors between these groups. Women taking aspirin regularly for preventive reasons may have a healthier lifestyle and may be more compliant users of medications, factors that are known to lead to too optimistic estimates of effects.2 It would therefore be interesting to evaluate the effect of aspirin on all-cause as well as cardiovascular- and malignancy-related mortality in patients taking aspirin for chronic headaches or musculoskeletal pain. In this subgroup, the use of aspirin is a necessity dictated by pain, which leads to regular intake, and its use is not related to a desire for general cardiovascular prevention among health-conscious persons. Because in this subgroup the reason for aspirin exposure was not related to the outcome of interest, the effect of aspirin may be more properly estimated. Furthermore, the method that was used for selecting control subjects may give rise to an overestimation of the effect of aspirin. Control subjects were all the participants who did not become a case subject (ie, who did not die) during follow-up in this closed cohort study, which is known to increasingly overestimate odds ratios when the disease incidence is larger than 5% to 10%.3,4 The mortality in the study by Chan et al1 was 12%. A simple approximate method to correct this bias can be used.5 Correspondence: Mr Snoep, Department of Clinical Epidemiology, C9-P, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, the Netherlands (J.D.Snoep@lumc.nl). References 1. Chan ATManson JEFeskanich DStampfer MJColditz GAFuchs CS Long-term aspirin use and mortality in women. Arch Intern Med 2007;167 (6) 562- 572PubMedGoogle ScholarCrossref 2. Baron JA Can aspirin keep mortality at bay? Arch Intern Med 2007;167 (6) 535- 536PubMedGoogle ScholarCrossref 3. Greenland SThomas DC On the need for the rare disease assumption in case-control studies. Am J Epidemiol 1982;116 (3) 547- 553PubMedGoogle Scholar 4. Lubin JHGail MH Biased selection of controls for case-control analyses of cohort studies. Biometrics 1984;40 (1) 63- 75PubMedGoogle ScholarCrossref 5. Zhang JYu KF What's the relative risk? a method of correcting the odds ratio in cohort studies of common outcomes. JAMA 1998;280 (19) 1690- 1691PubMedGoogle ScholarCrossref

Journal

Archives of Internal MedicineAmerican Medical Association

Published: Nov 26, 2007

References