BMJ 2001;323:42-46 ( 7 July )

Education and debate

Systematic reviews in health care

Assessing the quality of controlled clinical trials

This is the first in a series of four articles

Peter Jüni, research fellow ^a, Douglas G Altman, professor of statistics in medicine ^b, Matthias Egger, senior lecturer in epidemiology and public health medicine ^c. 

^a Department of Social and Preventive Medicine, University of Bern, Bern, 3012 Switzerland, ^b Imperial Cancer Research Fund Medical Statistics Group, Centre for Statistics in Medicine, Institute of Health Sciences, Oxford OX3 7LF, ^c Medical Research Council Health Services Research Collaboration, Department of Social Medicine, University of Bristol, Bristol BS8 2PR

Correspondence to: M Egger m.egger@bristol.ac.uk

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

The quality of controlled trials is of obvious relevance to systematic reviews. If the "raw material" is flawed then the conclusions of systematic reviews cannot be trusted. Many reviewers formally assess the quality of primary trials by following the recommendations of the Cochrane Collaboration and other experts. ^{1 2} However, the methodology for both the assessment of quality and its incorporation into systematic reviews and meta-analysis are a matter of ongoing debate.^3-5 In this article we discuss the concept of study quality and the methods used to assess quality.

Table Removed (Available Only in the Full Text)

Quality is a multidimensional concept, which could relate to the design, conduct, and analysis of a trial, its clinical relevance, or quality of reporting.⁶ The validity of the findings generated by a study clearly is an important dimension of quality. In the 1950s the social scientist Campbell proposed a useful distinction between internal and external validity (see box below). ^{7 8} Internal validity implies that . . . [Full text of this article]

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