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Use of a Marginal Structural Model to Determine the Effect of Aspirin on Cardiovascular Mortality in the Physicians' Health Study

Use of a Marginal Structural Model to Determine the Effect of Aspirin on Cardiovascular Mortality... The 1982–1988 aspirin component of the Physicians' Health Study, a randomized trial of aspirin and β-carotene in primary prevention of cardiovascular disease and cancer among 22,071 US male physicians, was terminated early primarily because of a statistically extreme 44% reduction in first myocardial infarction, with inadequate precision and no apparent effect on the primary endpoint, cardiovascular death. Because of the demonstrated efficacy of aspirin in secondary prevention of cardiovascular death, nonfatal cardiovascular events may simultaneously be time-dependent confounders and intermediate variables. Aspirin use is strongly influenced by these as well as other diseases, side effects, and cardiovascular risk factors. The authors used a marginal structural model with time-dependent inverse probability weights to estimate the underlying causal effect of aspirin on cardiovascular mortality. Although intention-to-treat analyses found no effect (rate ratio = 1.00, 95% confidence interval (CI): 0.72, 1.38), the estimated causal rate ratio was altered to 0.75 but remained nonsignificant (95% CI: 0.48, 1.16). As-treated analyses suggested a more modest effect of aspirin use (rate ratio = 0.90, 95% CI: 0.65, 1.25). Although the numbers of cardiovascular deaths were insufficient to evaluate this endpoint definitively, use of such methods holds much potential for controlling time-varying confounders affected by previous exposure. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png American Journal of Epidemiology Oxford University Press

Use of a Marginal Structural Model to Determine the Effect of Aspirin on Cardiovascular Mortality in the Physicians' Health Study

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References (29)

Publisher
Oxford University Press
Copyright
© Published by Oxford University Press.
ISSN
0002-9262
eISSN
1476-6256
DOI
10.1093/aje/155.11.1045
Publisher site
See Article on Publisher Site

Abstract

The 1982–1988 aspirin component of the Physicians' Health Study, a randomized trial of aspirin and β-carotene in primary prevention of cardiovascular disease and cancer among 22,071 US male physicians, was terminated early primarily because of a statistically extreme 44% reduction in first myocardial infarction, with inadequate precision and no apparent effect on the primary endpoint, cardiovascular death. Because of the demonstrated efficacy of aspirin in secondary prevention of cardiovascular death, nonfatal cardiovascular events may simultaneously be time-dependent confounders and intermediate variables. Aspirin use is strongly influenced by these as well as other diseases, side effects, and cardiovascular risk factors. The authors used a marginal structural model with time-dependent inverse probability weights to estimate the underlying causal effect of aspirin on cardiovascular mortality. Although intention-to-treat analyses found no effect (rate ratio = 1.00, 95% confidence interval (CI): 0.72, 1.38), the estimated causal rate ratio was altered to 0.75 but remained nonsignificant (95% CI: 0.48, 1.16). As-treated analyses suggested a more modest effect of aspirin use (rate ratio = 0.90, 95% CI: 0.65, 1.25). Although the numbers of cardiovascular deaths were insufficient to evaluate this endpoint definitively, use of such methods holds much potential for controlling time-varying confounders affected by previous exposure.

Journal

American Journal of Epidemiology – Oxford University Press

Published: Jun 1, 2002

Keywords: aspirin; bias (epidemiology); cardiovascular diseases; confounding factors (epidemiology); epidemiologic methods; mortality; myocardial infarction; CABG, coronary artery bypass graft; CI, confidence interval; MI, myocardial infarction; PTCA, percutaneous transluminal coronary angioplasty; RR, rate ratio

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