Variance and significance in large-scale online services
The Unofficial Google Data Science Blog
JANUARY 14, 2016
For this purpose, let’s assume we use a t-test for difference between group means. Effect size thus defined is useful because the statistical power of a classical test for $delta$ being non-zero depends on $e/sqrt{tilde{n}}$, where $tilde{n}$ is the harmonic mean of sample sizes of the two groups being compared.
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