AMSTAR is a tool for measuring the methodological quality of meta-analyses (range, 0–11); however, the score does not record the quality indicators of the individual meta-analyzed trials. This can result in bias pooled results. AMSTAR-Plus (range, 0–8) captures an additional six quality items that determine the content quality of the meta-analyzed trials.1

Reference:

1. Correll CU, Rubio JM, Inczedy-Farkas G, et al. Efficacy of 42 pharmacologic cotreatment strategies added to antipsychotic monotherapy in schizophrenia: systematic overview and quality appraisal of the meta-analytic evidence. JAMA Psychiatry 2017; 74: 675–684.