Positive Results Bias and Impact Factor in Ophthalmology

Previous studies in several fields of medicine have reported an association between the result of a trial (positive versus negative) and the impact factor of the journal in which it is published. The purpose of this study was to test the hypotheses that in the field of ophthalmology: (1) studies with positive results have a greater chance of being published in journals with a higher impact factor; (2) likewise, studies with a larger number of participants are more likely to be published in journals with a higher impact factor.

In this retrospective study, consecutive randomized, controlled trials conducted in the field of ophthalmology between 1 January 2010 and 1 January 2013 were retrieved from PubMed. Each study was classified as having either a positive or negative result. A positive result was defined as a study in which there was a statistically significant difference between groups (p < 0.05). The impact factor of the journal in which the study was published was retrieved. The number of patients enrolled and whether or not the trial was placebo controlled was documented as well.

Out of 2524 studies identified, 892 met the inclusion criteria. Studies with positive results were published in journals with a significantly higher impact factor than that of the journals in which negative result studies were published (p < 0.001). Studies with positive results had a slightly larger number of participants than studies with negative results (p = 0.028). In multiple regression analysis, the ranked impact factor was significantly predicted by the primary outcome (positive versus negative results) and the number of participants in a study (total R(2 )= 2.95, p < 0.001).

In the field of ophthalmology, articles with positive results are currently published in journals with a higher impact factor. This finding supports the ongoing occurrence of positive results bias in the field of ophthalmology.