What difference might retractions make? An estimate of the potential epistemic cost of retractions on meta-analyses

The extent to which a retraction might require revising previous scientific estimates and beliefs – which we define as the epistemic cost – is unknown. We collected a sample of 229 meta-analyses published between 2013 and 2016 that had cited a retracted study, assessed whether this study was included in the meta-analytic estimate and, if so, re-calculated the summary effect size without it. The majority (68% of N = 229) of retractions had occurred at least one year prior to the publication of the citing meta-analysis. In 53% of these avoidable citations, the retracted study was cited as a candidate for inclusion, and only in 34% of these meta-analyses (13% of total) the study was explicitly excluded because it had been retracted. Meta-analyses that included retracted studies were published in journals with significantly lower impact factor. Summary estimates without the retracted study were lower than the original if the retraction was due to issues with data or results and higher otherwise, but the effect was small. We conclude that meta-analyses have a problematically high probability of citing retracted articles and of including them in their pooled summaries, but the overall epistemic cost is contained.