The selective reporting of some outcomes but not others, depending on the nature and direction of the results The publication of research findings in a particular language, depending on the nature and direction of the results The citation or non-citation of research findings, depending on the nature and direction of the results The publication of research findings in journals with different ease of access or levels of indexing in standard databases, depending on the nature and direction of results. The multiple or singular publication of research findings, depending on the nature and direction of the results
The rapid or delayed publication of research findings, depending on the nature and direction of the results The publication or non-publication of research findings, depending on the nature and direction of the results The table below summarizes some different types of reporting biases. The contribution made to the totality of the evidence in systematic reviews by studies with non-significant results is as important as that from studies with statistically significant results. Statistically significant, ‘positive’ results that indicate that an intervention works are more likely to be published, more likely to be published rapidly, more likely to be published in English, more likely to be published more than once, more likely to be published in high impact journals and, related to the last point, more likely to be cited by others.
Reporting biases arise when the dissemination of research findings is influenced by the nature and direction of results. It has long been recognized that only a proportion of research projects ultimately reach publication in an indexed journal and thus become easily identifiable for systematic reviews. The dissemination of research findings is not a division into published or unpublished, but a continuum ranging from the sharing of draft papers among colleagues, through presentations at meetings and published abstracts, to papers in journals that are indexed in the major bibliographic databases (Smith 1999). The researchers also reported that Egger’s test showed no evidence that the results were significantly affected by publication bias.We refer to Chapter 10 of the Cochrane Handbook. Improvements in sleep latency did not vary between individual hypnotics. Non-benzodiazepine hypnotics showed a small improvement in subjective sleep latency although the change was not significant (−6.9 minutes, −26.0 to 12.4). When the results of the trials were combined, non-benzodiazepine hypnotics showed a significant improvement (reduction) in the main outcome of polysomnographic sleep latency compared with placebo (weighted mean raw difference −22.0 minutes, 95% confidence interval −33.0 to −11.0). Thirteen trials were eligible for inclusion. The main outcomes were polysomnographic and subjective measurements of sleep latency. Participants were adults with primary insomnia (transient or chronic).
Randomised controlled trials were included if they were double blind, placebo controlled, and had parallel treatment groups. Researchers undertook a meta-analysis of the effectiveness of non-benzodiazepine hypnotics, including eszopiclone, zaleplon, and zolpidem. Correspondence to: P Sedgwick p.sedgwicksgul.ac.uk.1Institute for Medical and Biomedical Education, St George’s, University of London, London, UK.Philip Sedgwick, reader in medical statistics and medical education.