Demonstration of deductive meta-analysis: ethanol intake and risk of myocardial infarction.

Meta-analyses should be analytic and deductive. In a review of the state of the science of meta-analysis in the previous volume of Epidemiologic Reviews, a list of definitions and synonyms of meta-analysis was given: "overview, pooling, data pooling, literature synthesis, data synthesis, quantitative synthesis, and quantitative review" (1, p. 154). Indeed, most metaanalyses are more synthetic than analytic: They produce a summary, such as an aggregate relative risk and 95 percent confidence interval, from a set of individual studies and stop there. Such a "meta-synthesis" has an inductive approach, i.e., generalization from a set of particular observations. By contrast, a deductive approach starts with alternative generalizations (hypotheses) and uses particular observations to discriminate among them. The causal hypothesis of primary interest is considered corroborated if competing hypotheses do not stand up to the evidence (2). The words "inductive" and "deductive" here have the meanings used in logic (3). Induction is the inference "If true for A, then true for B" when A is a part, sample, or special case of B. When epidemiologists infer