Explore statistical power, which in most cases requires NonCentral t calculations.

Click to display the central t distribution (blue) that applies when Ho is true, and/or the noncentral t distribution (red) that is appropriate when Ha is true. Display the two-tail rejection region for the statistical significance test, then the tail area(s) under the red curve that give statistical power. Vary df, alpha, and the noncentrality parameter (which is determined by the effect size, i.e. the distance between the null and alternative hypothesised mean values). You can also display the percentages of experiments that, if Ha is true, would be expected to give various significance test outcomes: These percentages may be surprising.