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.