Publication bias is a bias with regard to what is likely to be published, among what is available to be published. Not all bias is inherently problematic – for instance, a bias against publishing lies is often a desirable bias – but one problematic and much-discussed bias is the tendency of researchers, editors, and pharmaceutical companies to handle the reporting of experimental results that are positive (i.e. showing a significant finding) differently from results that are negative (i.e. supporting the null hypothesis) or inconclusive, leading to a misleading bias in the overall published literature.

This is usually a bias towards reporting significant results, despite the fact that studies with significant results do not appear to be superior to studies with a null result with respect to quality of design. It has been found that statistically significant results are three times more likely to be published than papers affirming a null result. It also has been found that the most common reason for non-publication is an investigator’s declining to submit results for publication (because of the investigator’s loss of interest in the topic, the investigator’s anticipation that others will not be interested in null results, etc.), a finding that underlines researchers’ role in publication bias phenomena.

In an effort to decrease this problem, some prominent medical journals require registration of a trial before it commences so that unfavorable results are not withheld from publication. Several such registries exist, but researchers are often unaware of them. In addition, attempts to identify unpublished studies have proved very difficult and often unsatisfactory. Another strategy suggested by a meta-analysis is caution in the use of small and non-randomized clinical trials because of their demonstrated high susceptibility to error and bias.

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