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Jonathan A C Sterne Medical Research Council Health Services Research
Collaboration, Department of Social Medicine, University of Bristol,
Bristol BS8 2PR
Correspondence to: J A C Sterne
jonathan.sterne@bristol.ac.uk
| The first 150 words of the full text of this article appear below. |
Studies that show a significant effect of treatment are more likely to be published, be published in English, be cited by other authors, and produce multiple publications than other studies.1-8 Such studies are therefore also more likely to be identified and included in systematic reviews, which may introduce bias.9 Low methodological quality of studies included in a systematic review is another important source of bias.10
All these biases are more likely to affect small studies than large
ones. The smaller a study the larger the treatment effect necessary for
the results to be significant. The greater investment of time and money
in larger studies means that they are more likely to be of high
methodological quality and published even if their results are
negative. Bias in a systematic review may therefore become evident
through an association between the size of the treatment effect and
study size
such associations may be
What can you learn from this BMJ paper? Read Leanne Tite's Paper+