BMJ  2007;334:94-96 (13 January), doi:10.1136/bmj.39057.406644.68

Practice

Clinical epidemiology notes

What is heterogeneity and is it important?

¹ BMJ, London WC1H 9JR

This is the first in a series of occasional articles explaining statistical and epidemiological tests used in research papers in the BMJ

The first 150 words of the full text of this article appear below.

Introduction

Three systematic reviews published in the BMJ, including one in this issue, have referred to heterogeneity and dealt with it in three different ways.^{1 2 3} So what is heterogeneity, and how do we assess its importance in a systematic review?

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 . . . [Full text of this article]

Statistical heterogeneity

How can you detect it and does it matter?

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There is no heterogeneity between steroids and antihistamines

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