Effect Size

The effect size is the degree of distance between the null hypothesis and alternative hypothesis distributions. The larger the effect size, the easier it is to detect a true difference between the two population means. The effect size is the only factor that influences power that is not under the investigator's control. The effect size just "is". We estimate the effect size (anticipated difference between our null hypothesis and alternative hypothesis) from reading the literature.

Here is our statistical power graph. Let's conduct a test with a larger effect size and see what happens. The alpha-level and sample size will remain the same.