Publication bias and time-trend bias in meta-analysis of bicycle helmet efficacy: A re-analysis of Attewell, Glase and McFadden, 2001

► A meta-analysis of the effects of bicycle helmets published in Accident Analysis and Prevention in 2001 has been re-analysed. ► The re-analysis found that the original meta-analysis was influenced by publication bias and time trend bias it did not control for. ► When these sources of bias are controlled for, and new studies added to the analysis, the effects attributed to bicycle helmets become considerably smaller than originally reported. ► The findings of this meta-analysis are not consistent with a recently published Cochrane review.