Test statistics and effect sizes
The two statistical concepts are distinct.
Researchers may confuse a test statistic for a standardised effect size.
Test statistics and standardised effect sizes are distinct. The two figures may have similar formulae, but represent different things. This article shows the example of comparing mean averages in independent samples.
Spot the difference
Researchers are often interested in how two independent samples are different from another. For example, they may wish to compare the efficacy of a drug against a competitor or placebo.
What is the difference between test statistics and effect sizes? Here, I compare the t-stat (a test statistic) and Cohen’s d (a standardised effect size).
You do not need to understand mathematical formulae for this part. You only need to be able to spot differences. This is the t-stat:
This is the formula for Cohen’s d:
In both cases, I have used the pooled standard deviation from both samples.
