Explore NonCentral t distributions and calculate accurate probabilities.

The familiar t distribution has the single parameter df. NonCentral t distributions have in addition a noncentrality parameter. Here you can use the controls to see how the shape of the noncentral distribution (red) changes with df and the noncentrality parameter. Click boxes to display or hide a central distribution (blue), for comparison, and various other features. You can also display accurate tail probability values for your chosen df, noncentrality parameter, and t values. Noncentral t distributions are essential for statistical power and for CIs for Cohen’s d. For more, see our journal article.