Editors: Jonathan AC Sterne, Matthias Egger and David Moher on behalf of the Cochrane Bias Methods Group.
Key points
Only a proportion of research projects will be published in sources easily identifiable by authors of systematic reviews. Reporting biases arise when the dissemination of research findings is influenced by the nature and direction of results.
The contribution made to the totality of the evidence in systematic reviews by studies with statistically non-significant results is as important as that from studies with statistically significant results.
The convincing evidence for the presence of several types of reporting biases (outlined in this chapter) demonstrates the need to search comprehensively for studies that meet the eligibility criteria for a Cochrane review.
Prospective trial registration, now a requirement for publication in many journals, has the potential to substantially reduce the effects of publication bias.
Funnel plots can be used for reviews with sufficient numbers of included studies, but an asymmetrical funnel plot should not be equated with publication bias.
Several methods are available to test for asymmetry in a funnel plot and recommendations are included in the chapter for selecting an appropriate test.
Table 10.1.a: Definitions of some types of reporting biases
10.2 Types of reporting biases and the supporting evidence
10.3 Avoiding reporting biases
10.4 Detecting reporting biases