Clinical heterogeneity in random‐effect meta‐analysis: Between‐study boundary estimate problem

Random‐effect meta‐analysis is commonly applied to estimate overall effects with unexplained heterogeneity across studies. However, standard methods, including (restricted) maximum likelihood (ML or REML), frequently produce (near) zero estimates for between‐study variance parameters. Consequently, these methods are reduced to simple and unrealistic fixed‐effect models, resulting in an ignorance of the substantial clinical heterogeneity and...