What is heterogeneity and is it important?

Abstract

Clinical heterogeneity Sometimes trials are just looking at different concepts. Reviewers might set out to summarise interventions for improving patients' ability to make treatment choices; the trials, however, might have covered diverse interventions, such as information leaflets, CD Roms, counselling sessions with a nurse, and training in consultation techniques for doctors. Although the interventions try to achieve the same end result (to improve patients' ability to make choices), they are different in nature. In theory, we could add all the trials in this review together and come up with a number, but would this be useful? Would the averaged number apply to all these diverse interventions? The interventions are so different that combining them does not make clinical sense. This is an example of clinical heterogeneity. Other circumstances that may give rise to clinical heterogeneity include differences in selection of patients, severity of disease, and management. Judgments about clinical heterogeneity are qualitative, do not involve any calculations, and can be made by putting forward a convincing argument about similarities (or differences) between the trials.