Figure 2. Screenshot of the micro-learning module
ADDITIONAL INFORMATION
The particular definition used in Cochrane Reviews and in this tutorial is the effect size known in social sciences as Hedges’ g , which is similar to the effect size so-called Cohen’s d with a small-sample correction. Hedges’ g uses a pooled SD in the denominator, which is an estimate of the SD based on outcome data from both intervention groups, assuming that the SDs in the two groups are similar [7]. In contrast, Glass’ delta (Δ) uses only the SD from the comparator group, on the basis that if the experimental treatment affects between-person variation, then such an impact of the treatment should not influence the effect estimate.
All these effect measures referred to as SMDs can be calculated by hand or in any statistical package. Statistical packages in R software include metafor [10], esc [11], orcompute.es [12]. A hands-on useful resource is thebookdown of Harrer et al. (2021) [13], which serves an accessible introduction into how meta-analyses are covered, including different SMD calculation, and pooling methods with examples.