I wrote this entry when I wanted to QC my WWC effect size calculation using R and SAS.
WWC standard doc
https://ies.ed.gov/ncee/wwc/Docs/referenceresources/wwc_procedures_v2_1_standards_handbook.pdf
Page 37.
In SAS:
data test;
N_Yes=4300;
Mean_Yes=400;
StdDev_Yes=200;
N_No=4000;
Mean_NO=300;
StdDev_NO=200;
/*create statistics*/
mean_dif=(Mean_Yes-Mean_NO);
/*Standardized effects*/
g1=((N_Yes-1)*(StdDev_Yes*StdDev_Yes)) +((N_No-1)*(StdDev_No*StdDev_No));
g2=N_Yes + N_No -2;
g3=sqrt(g1/g2);
WWC_effect=mean_dif/g3;
run;
In R:
FGC_l_N_YES=4300
FGC_l_Mean_YES=400
FGC_l_StdDev_YES=200
REG_l_N_YES=4000
REG_l_Mean_YES=300
REG_l_StdDev_YES=200
simple_gap=FGC_l_Mean_YES-REG_l_Mean_YES
g1<- ((FGC_l_N_YES-1)*(FGC_l_StdDev_YES*FGC_l_StdDev_YES))+((REG_l_N_YES-1)*(REG_l_StdDev_YES*REG_l_StdDev_YES))
g2= FGC_l_N_YES + REG_l_N_YES -2
g3= sqrt(g1/g2)
simple_gap_std= simple_gap/g3
simple_gap_std
g1
g2
g3
simple_gap_std
My web calculator
https://www.estat.us/file/calc_t_test1b.php
Treatment N:4300
Treatment mean:400
Treatment SD:200
Comparison N:4000
Comparison mean:300
Comparison SD:200
The group mean difference:100
[RESULTS FOR CONTINUOUS OUTCOME]
Probability: Under Development (Still working on this)
T-score is: 22.761
Significant at alpha 0.05 (two tail test;I used a z-test and ignored degree freedom; threshold 1.96)
T-test (the same test as above but with three thresholds)T 1.96, 2.576, 3.291, each for p=0.05, 0.01, 0.001
Sig at p=.001***
Hedges d 0.5