An Assessment of Publication Bias Using a Sample of Published Clinical Trials

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Abstract
The potential magnitude of publication bias has been examined with a consecutive sample of published cancer clinical trials. The analysis is based on the premise that the magnitude of the true treatment effect is unrelated to design features of the study, in particular sample size. This assumption permits an analysis based only on published studies. Three primary endpoints are examined: overall patient survival, disease-free survival, and tumor response rate. There are striking trends for each endpoint, with small studies appearing to possess large treatment effects and large studies possessing relatively small effects. It is believed that these differences are primarily due to publication bias. The bias is very large: Absolute differences observed were 41% for overall survival, 79% for disease-free survival, and 17% for response rates. Other study features have been examined that might be associated with bias, or that might be responsible for the striking trends regarding sample size. The result...

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