pplying the one way robust Anova of the WRS2 package for a specific dataset I get the following results:

Code: 
> t1way(totspcam ~ bono_recibido, data = spend_red)
Call:
t1way(formula = totspcam ~ bono_recibido, data = spend_red)

Test statistic: 49.4939 
Degrees of Freedom 1: 2 
Degrees of Freedom 2: 175.08 
p-value: 0
Explanatory measure of effect size: 0.2
And with the bootstrap version:

Code: 
> t1waybt(totspcam ~ bono_recibido, data = spend_red)
Call:
t1waybt(formula = totspcam ~ bono_recibido, data = spend_red)

Effective number of bootstrap samples was 599.

Test statistic: 49.4939 
p-value: 0 
Variance explained 0.036 
Effect size 0.191
Now, I have bronswed on the web but it seems to me that it is nowhere specified what indicator has been used to compute the effect size of 0.19.

Question: Does anyone know what type of indicator has been used for the effect size and what it represents??