This Demonstration provides a visualization of power analysis for a two-tailed, two-sample

-test. A two-sample

-test is a hypothesis test to check for statistical significance between two samples. The red curve is the

distribution of the null hypothesis. In a two-sample test, this is normally the control sample. The blue curve is the noncentral

distribution of the alternative hypothesis. This is normally the experimental sample. The effect size and the sample size determine the noncentrality parameter

. This value appears above the alternative hypothesis distribution. The two vertical lines represent the critical

values. The area outside these values represents statistical significance for the given

-value. Any part of the noncentral distribution outside the given

values represents experiments that would be considered statistically significant. This total area is referred to as the power.