15.5 Hedges’ g from the Mean and SE

When calculating Hedges’ g from the Mean and Standard Error, we simply make use of the fact that the Standard error is not much more than the Standard Deviation when the sample size is taken into account (Thalheimer and Cook 2002):

\[SD = SE\sqrt{n_c}\]

We can calculate Hedges’ g using the esc_mean function with the following parameters:

  • grp1m: The mean of the first group.
  • grp1se: The standard error of the first group.
  • grp1n: The sample size of the first group.
  • grp2m: The mean of the second group.
  • grp2se: The standard error of the second group.
  • grp2n: The sample size of the second group.
  • 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_se(grp1m = 8.5, grp1se = 1.5, grp1n = 50,
  grp2m = 11, grp2se = 1.8, grp2n = 60, es.type = "g")
## Effect Size Calculation for Meta Analysis
##      Conversion: mean and se to effect size Hedges' g
##     Effect Size:  -0.1998
##  Standard Error:   0.1920
##        Variance:   0.0369
##        Lower CI:  -0.5760
##        Upper CI:   0.1765
##          Weight:  27.1366


Thalheimer, Will, and Samantha Cook. 2002. “How to Calculate Effect Sizes from Published Research: A Simplified Methodology.” Work-Learning Research 1.