Meta-analysis in a nutshell : techniques and general findings

The purpose of this note is to introduce the technique and main findings of meta-analysis to the reader, who is unfamiliar with the field and has the usual objections. A meta-analysis is a quantitative survey of a literature reporting estimates of the same parameter. The funnel showing the distribution of the results is normally amazingly wide given their t-ratios. Little of the variation can be explained by the quality of the journal or by the estimator used. The funnel has often asymmetries consistent with the most likely priors of the researchers, giving a publication bias.