Preventive medicine
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Preventive medicine · Jan 1991
Meta AnalysisEstrogen replacement therapy and coronary heart disease: a quantitative assessment of the epidemiologic evidence.
Considerable epidemiological evidence has accumulated regarding the effect of postmenopausal estrogens on coronary heart disease risk. Five hospital-based case-control studies yielded inconsistent but generally null results; however, these are difficult to interpret due to the problems in selecting appropriate controls. Six population-based case-control studies found decreased relative risks among estrogen users, though only 1 was statistically significant. ⋯ Overall, the bulk of the evidence strongly supports a protective effect of estrogens that is unlikely to be explained by confounding factors. This benefit is consistent with the effect of estrogens on lipoprotein subfractions (decreasing low-density lipoprotein levels and elevating high-density lipoprotein levels). A quantitative overview of all studies taken together yielded a relative risk of 0.56 (95% confidence interval 0.50-0.61), and taking only the internally controlled prospective and angiographic studies, the relative risk was 0.50 (95% confidence interval 0.43-0.56).
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The analysis of cancer prevention trials necessitates specialized procedures. Differences in the analysis plan between cancer prevention and therapy trials are emphasized. Discussion is focused upon (a) how trial conduct influences the analysis, (b) how noncompliance affects the analysis and the considerations this raises during the design and conduct of the trial, (c) how delays in the effect of the intervention impinges upon the analysis, and (d) statistical methods available to carry out the analysis. The analysis of a cancer prevention trial represents a final step in the evaluation of the study intervention and requires an adaptive planning procedure.