• public health

Epidemiology is widely perceived as a public health discipline within which methodologymatters.1 Methods dominate educational curriculums and influential textbooks.2 3Epidemiological societies regularly feature methods sessions at their national and international meetings and, at least informally, the discipline recognises the methodologists who study the methods and the practitioners who use them. It follows that epidemiological methods, whether quantitative (for example, meta-analysis or logistic regression) or qualitative (for example, causal inference or narrative reviews), have a theoretical side and a more practical side. The theory behind a method and especially how that method should be practised “in theory” are discussed in textbooks and journal articles; methodological standards and guidelines are good examples. How a method is actually practised is found in its applications, in analytical studies, reviews, and other publications. The relation between these accounts—the extent to which practice matches theory—is the starting point of this paper.

Three methods are of particular interest: meta-analysis, causal inference, and techniques for systematic narrative literature reviews. These methods were selected because serious concerns have been raised about how each is practised.4-6 These are also closely related methods, often appearing together in the same publication, typically a review paper, textbook chapter, or technical report within which a body of evidence is summarised and interpreted.7 8 Nevertheless, each of these methods is distinct enough to have a recognisable theoretical literature and observable practice patterns.

Perhaps the most important reason for looking carefully at the relation between how these methods are practised and how they are “supposed” to be practised is the key part they play in the assessment and interpretation of scientific evidence. These methods are central to the search for causal determinants of disease and for ways to use that knowledge to improve public health.

Public health and clinical …