Standardised mean differences were derived to take account of the variety of behavioural outcome measures included and random effect models adopted in view of variability of the intervention and target populations across studies. (capmh.biomedcentral.com)
A multilevel random effects model accounts for the hierarchical structure of the data, in which the effect sizes or study results (the lowest level) are nested within studies (the highest level). (link.springer.com)
To deal with dependency of study results, we used a multilevel random effects model for the calculation of combined effect sizes and moderator - analyses (Hox 2002; Van den Noortgate and Onghena 2003). (link.springer.com)