Hi,

comparing the average of 2 groups when we

How do you calculate the

or just a simple average

comparing the average of 2 groups when we

**know**each group's standard deviation:**σ1, σ2****Cohen’s effect Size = | avg(x1)- avg(x2)| / σ pooled**How do you calculate the

**σ pooled**for**2 sample z test**?**σ pooled^2= (n1σ1^2+n2σ2^2)/(n1+n2) {similar to t-test}**or just a simple average

**σ pooled =(σ1+σ1)/2**?
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