Abstract
Because negative findings have less chance of getting published, available studies tend to be a biased sample. This leads to an inflation of effect size estimates to an unknown degree. To see how meta-analyses in education account for publication bias, we surveyed all meta-analyses published in the last five years in the Review of Educational Research and Educational Research Review. The results show that meta-analyses usually neglect publication bias adjustment. In the minority of meta-analyses adjusting for bias, mostly non-principled adjustment methods were used, and only rarely were the conclusions based on corrected estimates, rendering the adjustment inconsequential. It is argued that appropriate state-of-the-art adjustment (e.g., selection models) should be attempted by default, yet one needs to take into account the uncertainty inherent in any meta-analytic inference under bias. We conclude by providing practical recommendations on dealing with publication bias.
Highlights
Because any single study seldom provides conclusive evidence, meta-analyses are seen as the most objective way to settle substantive scientific questions
Field-wide evidence synthesis employing eight hundred meta-analyses leads to the conclusion that almost everything works, with an average effect size of d = .40 [1]
We reviewed all the empirical papers published from January 2016 to December 2020 in two flagship educational journals specializing in systematic review studies, the Review of Educational Research and Educational Research Review
Summary
Because any single study seldom provides conclusive evidence, meta-analyses are seen as the most objective way to settle substantive scientific questions. Meta-analysis is a way to synthesize evidence from a set of studies examining the same underlying effect in a consistent and transparent manner. If such a set of studies comes from a systematic review of the literature, the goal is usually to provide a generalizable inference about a target effect, as it tends to be studied. Pre-registered large scale randomized controlled trials (RCTs) of most promising educational interventions (required by the funders to be published irrespective of the result) yield an average effect size of just d = .06 [2].
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