What is publication bias ?
Publication bias is usually defined as the tendency from authors to
publish studies with significant results (1).
In this paper the authors survey 26 studies on “publication bias”
(2). To our opinion, not all the included studies are dealing with the
real publication bias, e.g., studies on language bias. Moreover, this
review includes studies on both publication bias and abstract-based
These two publication biases should not be merged since abstracts
presented or even only submitted are not representative of research. “Not
interesting results” would even not be submitted in abstract form. From
Easterbrook study we learn than half of studies with “non significant
trend” or “null” outcomes are not presented. When studying abstracts,
statistically significant results are over-represented (64% vs. 54% when
considering all research). (3) Abstract-based publication bias may
underestimate true research-based publication bias.
The field of publication bias has revealed to be broader than
expected. There may be now a need to clearly define publication bias as
well as sub-categories: outcome reporting bias(significant results are
selected among study outcomes to be published) (4), language bias
(significant results are published in english), database bias (significant
results are more easily retrieved through databases) (5), prestige bias
(significant results are published in higher impact factor journal),
redundant publication bias (significant results are published in more than
What about an “oral presentation bias”?
1. Dickersin K. The existence of publication bias and risk factors
for its occurrence. Jama 1990;263:1385-9.
2. Dubben HH, Beck-Bornholdt HP. Systematic review of publication
bias in studies on publication bias. BMJ 2005. doi:
3. Easterbrook PJ, Berlin JA, Gopalan R, Matthews DR. Publication
bias in clinical research. Lancet 1991;337:867-72.
4. Chan AW, Krleza-Jeric K, Schmid I, Altman DG. Outcome reporting
bias in randomized trials funded by the Canadian Institutes of Health
Research. Cmaj 2004;171:735-40.
5. Nieminen P, Isohanni M. Bias against European journals in medical
publication Databases. Lancet 1999;353:1592.
Competing interests: No competing interests