The extent of hidden or unpublished adverse events data: a methodological review




Poster session 3


Tuesday 25 October 2016 - 10:30 to 11:00


All authors in correct order:

Golder S1
1 Cochrane Adverse Effects Methods Group, UK
Presenting author and contact person

Presenting author:

Su Golder

Contact person:

Abstract text
Background: Publication and reporting biases may pose serious threats to the validity of systematic reviews of adverse events.

Objectives: To ascertain whether we can quantify the under-reporting of adverse events in the medical literature and measure the impact this has on systematic reviews of adverse events.

Methods: A systematic review of studies assessing the quantity or impact of unpublished adverse events data was undertaken. Studies were identified from 15 databases, handsearching, reference checking, internet searches and contacting experts. Search results were sifted independently by two reviewers and the quality assessment tool was derived in-house.

Results: From 4344 records, 27 methodological evaluations met the inclusion criteria. Ten compared numbers of adverse events in matched published and unpublished documents. The percentage of adverse events that would have been missed, had an analysis relied only on the published versions, varied between 43% and 100% with a median of 57%. Two other studies demonstrated that there are also substantially more types of adverse events reported in unpublished than published documents.
Nine studies compared the proportion of trials reporting adverse events by publication status. The median percentage of published documents with adverse events information was 46% compared to 95% in the corresponding unpublished documents. There was a similar pattern with unmatched studies where 43% of published studies contained adverse events information compared to 83% of unpublished studies.
There were 15 meta-analyses that reported the odds ratios/risk ratios with and without unpublished data. Inclusion of unpublished data increased the precision of the pooled estimates (narrower 95% confidence intervals) in 13 of the 15 pooled analyses.

Conclusions: There is strong evidence that much of the information on adverse events remains unpublished and that the number and range of adverse events is higher in unpublished than in published versions of the same study. The inclusion of unpublished data can reduce the imprecision of pooled effect estimates during meta-analysis of adverse events.