Instructions for Power Applets


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  1. To start, press the Draw! button.
  2. The applet will draw three curves representing three different sample sizes: n1, n1-4, and n1+4.
  3. The curves in the lower pane represent the densities under the null (top) and alternative (bottom) hypothesis.
    1. The area shaded in GREEN is the Type I error rate ().
    2. The area shaded in BLUE is Power.
  4. Placing the mouse pointer over the applet creates crosshairs on one of the curves.
  5. Moving the mouse traces the path of the curve for different values of Delta.
  6. To freeze the crosshairs, simply single-click on the applet.
  7. To move to the next curve, simply double-click on the applet.
  8. To remove the crosshair entirely, unselect the Crosshairs checkbox.
  1. Two-Sample:
    %n1 represents the proportion n2 (the second sample size) as a proportion of n1 (e.g. %n1=100 implies equal sample size; %n1=50 implies n2 is half of n1.)
  2. Proportions:
    For the one-sample test when n < 41 the two densities in the lower pane are overlaid with the theoretical binomial distributions.
  3. T-test:
    For the two-sample case, choosing Unequal Variances uses the Satterthwaite approximation for degrees of freedom.
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