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Citation rate of clinical studies is skewed towards positive outcomes

Making all clinical data, regardless of outcome, available to the public is one of the edicts of The World Health Organization and is a key factor in the drive for greater data transparency. But what happens after the results have been published? Unfortunately, a recent study reported in Trials suggests that positive data will be cited much more often than negative or neutral results and therefore will undoubtedly reach a far greater audience.

Misemer et al. looked at large clinical trials investigating thrombolytic agents for the treatment of acute stroke. Out of eight studies identified for alteplase: two reported positive outcomes, two negative and four were neutral. The citation rates for the studies with positive results were greater than the neutral and negative trials, by approximately three- and ten-times, respectively. The authors acknowledge that the context of the citations was not investigated so “to some extent a high citation rate might be a marker of controversy rather than influence”. Also, other factors, such as publication journal and author group may have an impact on citation rate. However, there does appear to be a trend for the repeated citation of trials with positive results which could influence clinical decision making. The authors highlight the importance of the publication of high-quality systematic reviews that summarise all available data. They suggest that everyone in the publication industry (authors, editors and peer reviewers) should be aware of citation bias and ensure that data selected for inclusion in scientific manuscripts “reflect a complete and balanced picture of the available evidence”.

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Summary by Jo Chapman, PhD from Aspire Scientific.

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