Publication Bias

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Publication bias, a type of reporting bias, is defined by the Cochrane Collaboration[1] as "publication or non-publication of research findings, depending on the nature and direction of the results" and by Dickersin[2] as "the tendency on the parts of investigators, reviewers, and editors to submit or accept manuscripts for publication based on the direction or strength of the study finding." It was first postulated in the psychology[3] and education[4] literature, but has since been shown to be a factor in medicine as well.[5]

Reasons for non-publication[6]

  • Researchers report reason for not writing up negative results is lack of interest
  • Peer-reviewers more likely to recommend studies with positive results
  • Rejection of manuscripts with negative results infrequently cited
  • Source of Funding is significantly correlated with publication
 - Drug-company sponsored research less likely to be published
 - Drug-company sponsored research more likely to favor sponsor

Calls for clinical trial registration

One mechanism that has been proposed to counteract publication bias is mandatory registration of clinical trials prior to their onset. In 2004, the International Committee of Medical Journal Editors (ICMJE) published a statement announcing that their member journals would begin requiring "... as a condition of consideration for publication, registration in a public trials registry. Trials must register at or before the onset of patient enrollment."[7] The 2013 World Medical Association Declaration of Helsinki included the statement that "Every research study involving human subjects must be registered in a publicly accessible database before recruitment of the first subject."[8]

Unfortunately, recent studies have shown that this requirement is frequently ignored. As an example, a recent study of cardiovascular trial registration[9] found:

  • Less than 50% of trials reported as registered
  • Registered trials tended to be larger
  • Registered trials more likely to "report strong methodological characteristics"
  • Registered trials were less likely to report positive findings (52% vs 70.5%)


  1. Sterne JAC, Egger M, Moher D (editors). Chapter 10: Addressing reporting biases. In: Higgins JPT, Green S (editors). Cochrane Handbook for Systematic Reviews of Intervention. Version 5.1.0 (updated March 2011). The Cochrane Collaboration, 2011. Available from
  2. Dickersin K. The existence of publication bias and risk factors for its occurrence. JAMA. 1990, Mar 9;263(10):1385-1389.
  3. Sterling TD. Publication decisions and their possible effects on inferences drawn from tests of significance – or vice versa. Journal of the American Statistical Association 1959;54:30-34.
  4. Smith ML. Publication bias and meta-analysis . Evaluation Educ. 1980;4:22-24.
  5. Simes RJ. Confronting publication bias: a cohort design for meta-analysis. Statistics in Medicine 1987;6:11-29.
  6. Dickersin K, Chalmers I. Recognising, investigating and dealing with incomplete and biased reporting of clinical research: from Francis Bacon to the WHO. J R Soc Med. 2011;104(12):532-538
  7. DeAngelis CD, Drazen JM, Frizelle FA, et al. Clinical Trial Registration: A Statement From the International Committee of Medical Journal Editors. JAMA. 2004;292(11):1363-1364.
  8. World Medical Association. World Medical Association Declaration of Helsinki: Ethical Principles for Medical Research Involving Human Subjects. JAMA. 2013;310(20):2191-2194.
  9. Emdin C, Odutayo A, Hsiao A, et al. Association of Cardiovascular Trial Registration With Positive Study Findings: Epidemiological Study of Randomized Trials (ESORT). JAMA Intern Med. 2015;175(2):304-307.

Submitted by Jennifer Aucoin