Evaluating the quality of medical evidence in real-world contexts.

How should the quality of medical evidence be evaluated? Proponents of evidence-based medicine advocate the use evidence hierarchies to rank the quality of evidence on the basis that certain methods produce more reliable evidence. Some criticisms of this approach focus on whether certain methods deserve their place in the hierarchy, while others claim that evidence hierarchies should be abandoned in favour of other evidence assessment techniques. We claim that this debate pays insufficient attention to the real-world contexts in which medical decisions are made. To address this limitation, we explore the value of using evidence hierarchies and other evidence assessment techniques in differing contexts of medical decision making and argue that the way in which the quality of medical evidence should be evaluated depends on context. Focusing the discussion of the evaluation of medical evidence on real-world contexts has implications for the viability of the principle of total evidence.