Footprint of publication selection bias on meta-analyses in medicine, environmental sciences, psychology, and economics.

Publication selection bias undermines the systematic accumulation of evidence. To assess the extent of this problem, we survey over 68,000 meta-analyses containing over 700,000 effect size estimates from medicine (67,386/597,699), environmental sciences (199/12,707), psychology (605/23,563), and economics (327/91,421). Our results indicate that meta-analyses in economics are the most severely contaminated by publication selection bias, closely followed by meta-analyses in environmental sciences and psychology, whereas meta-analyses in medicine are contaminated the least. After adjusting for publication selection bias, the median probability of the presence of an effect decreased from 99.9% to 29.7% in economics, from 98.9% to 55.7% in psychology, from 99.8% to 70.7% in environmental sciences, and from 38.0% to 29.7% in medicine. The median absolute effect sizes (in terms of standardized mean differences) decreased from d = 0.20 to d = 0.07 in economics, from d = 0.37 to d = 0.26 in psychology, from d = 0.62 to d = 0.43 in environmental sciences, and from d = 0.24 to d = 0.13 in medicine.

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for inclusion, and only in 34% of these meta-analyses (13% of total) the study was explicitly excluded because it had been retracted.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.

Meta-assessment of bias in science.

Numerous biases are believed to affect the scientific literature, but their actual prevalence across disciplines is unknown. To gain a comprehensive picture of the potential imprint of bias in science, we probed for the most commonly postulated bias-related patterns and risk factors, in a large random sample of meta-analyses taken from all disciplines. The magnitude of these biases varied widely across fields and was overall relatively small. However, we consistently observed a significant risk of small, early, and highly cited studies to overestimate effects and of studies not published in peer-reviewed journals to underestimate them. We also found at least partial confirmation of previous evidence suggesting that US studies and early studies might report more extreme effects, although these effects were smaller and more heterogeneously distributed across meta-analyses and disciplines. Authors publishing at high rates and receiving many citations were, overall, not at greater risk of bias. However, effect sizes were likely to be overestimated by early-career researchers, those working in small or long-distance collaborations, and those responsible for scientific misconduct, supporting hypotheses that connect bias to situational factors, lack of mutual control, and individual integrity. Some of these patterns and risk factors might have modestly increased in intensity over time, particularly in the social sciences. Our findings suggest that, besides one being routinely cautious that published small, highly-cited, and earlier studies may yield inflated results, the feasibility and costs of interventions to attenuate biases in the literature might need to be discussed on a discipline-specific and topic-specific basis.