## 15.1 Hedges’ g from the Mean and SD

To calculate Hedges’ g from the Mean, Standard Deviation, and $$n_{group}$$ of both trial arms, we can use the esc_mean_sd function with the following parameters.

• grp1m: The mean of the first group (e.g., the intervention).
• grp1sd: The standard deviation of the first group.
• grp1n: The sample size of the first group.
• grp2m: The mean of the second group.
• grp2sd: The standard deviation of the second group.
• grp2n: The sample size of the second group.
• totalsd: The full sample standard deviation, if the standard deviation for each trial arm is not reported
• es.type: the effect measure we want to calculate. In our case this is "g". But we could also calculate Cohen’s d using "d".

Here’s an example

esc_mean_sd(grp1m = 10.3, grp1sd = 2.5, grp1n = 60,
grp2m = 12.3, grp2sd = 3.1, grp2n = 56, es.type = "g")
##
## Effect Size Calculation for Meta Analysis
##
##      Conversion: mean and sd to effect size Hedges' g
##     Effect Size:  -0.7082
##  Standard Error:   0.1916
##        Variance:   0.0367
##        Lower CI:  -1.0837
##        Upper CI:  -0.3326
##          Weight:  27.2374