T-test Calculator for RCTs
Kaz's calculator program
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What Works Clearinghouse Comparison of Group means

Updated December 28, 2022

This program compares two group means (or proportions) and calculates a standardized group difference value. If continous variable, the program uses Hedges' g. If binary, Cox Index.
The description of Hedges’ g (used when interval scale) or Cox Index (when binary) are here. It starts from page 15 and most of it is on page 16.


You can see the algorithm I used for calculation here.
PHP syntax I used

This program does not care if a variable is a continuous or binary variable. The result page will give you two sets of results. If your variable is a continous variable, look at the result for continuous variable. If binary, look at the result for a binary variable. If your variable is a binary variable, the program assumes that YES is coded as 1 and NO is coded as 0. If binary, the result will not be affected by SD values, but the program will not run if SD values are empty. I would just enter values that you got from your procedure (or any values).

Treatment group N: Treatment group mean: Treatment group SD:
Control group N: Control group mean: Control group SD:
WWC procedures handbook (see page. 14)
WWC standards slides (Definition of small sample size correction, slide 14)