«There is strong evidence that much of the information on adverse events remains unpublished and that the number and range of adverse events is higher in unpublished than in published versions of the same study»: this is the conclusion of a study recently published on the Open Access journal PLOS Medicine, supported by the National Institute for Health Research. «The extent of “hidden” or “missing” data prevents researchers, clinicians, and patients from gaining a full understanding of harm, and this may lead to incomplete or erroneous judgements on the perceived benefit to harm profile of an intervention» write Su Golder and colleagues from the University of York, in the UK.
The researchers conducted a systematic review to measure the adverse events reported in peer-reviewed publications and in unpublished documents such as regulatory websites, trial registries, as well gray literature such as conference proceedings and press releases. Out of the total of over 5.000 records retrieved, 28 studies met the inclusion criteria from 31 publications: the studies that looked at differences regarding adverse events all concluded that information on adverse events is more often present in unpublished materials than in published material. «There were 8 included studies (from 9 publications and representing 10 comparisons) that compared the number of studies reporting adverse events in the published and matched unpublished documents. The percentage of studies reporting adverse events was higher in all cases in the unpublished versions than the published versions. The median percentage of published sources with adverse events information was 46% compared to 95% of the corresponding unpublished documents. A similar pattern emerged when the analysis was restricted to serious adverse events» the authors write. In detail, peer-reviewed articles failed to report 43% to 100% (median, 64%) of adverse events associated with medical treatments, including 2% to 100% of serious ones.
«Our review demonstrates the urgent need to progress towards full disclosure and unrestricted access to information from clinical trials» Golder and colleagues conclude. «Although improvements have been made in the accessibility of data, there are still major barriers and issues to contend with».