This is an interactive program designed to illustrate the basic principles of what controls power. Here, we assume that under the null, the statistic is distributed as a standard normal with mean zero and variance one, while under the alternative, the statistic is distributed as a standard normal with a shifted mean. Power is a function of the mean under the alternative hypothesis and the desired significance level. The 'Options' box allows the user to select the desired significance level using the radio buttons, and to set the mean under the alternative hypothesis using the slider.
This is a modified version of the 'tkdensity' demo from the 'tcltk' package.
A graph is drawn which reflects the user's choices. The resulting power is displayed in the title line of the graph, as well as the mean under the alternative hypothesis. The red line indicates the density under the null hypothesis (mean = 0), and the black line indicates the density under the alternative hypothesis. The vertical blue line indicates the significance threshold.
Daniel E. Weeks