Four decades of research and hundreds of studies speak to the power of post-event misinformation to bias eyewitness accounts of events (see e.g.Loftus' summary, 2005).A subset of this research has explored if the adverse influence of misinformation on remembering can be undone or at least reduced through a later warning about its presence.We metaanalyzed 25 such post-warning studies (including 155 effect sizes) to determine the effectiveness of different types of warnings and to explore moderator effects.Key findings were that (1) post-warnings are surprisingly effective, reducing the misinformation effect to less than half of its size on average.(2) Some types of post-warning (following a theoretical classification) seem to be more effective than others, particularly studies using an enlightenment procedure (Blank, 1998).(3) The post-warning reduction in the misinformation effect reflects a specific increase in misled performance (relative to no warning), at negligible cost for control performance.We conclude with a discussion of theoretical and practical implications.
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Blank et al. (2014) studied this question.