Two Variances: Power Calculation Results - Quick Tab

Calculating Power

Select the Quick tab of the Two Variances: Power Calculation Parameters dialog box to access options to interactively view the results of power calculations and generate plots of power as a function of quantities that affect power in practice.

X-Axis Graphing Parameters. The entries in the boxes under X-Axis Graphing Parameters establish the start value, end value, and number of steps on the X-axis for the graphs specified under Power Charts.

Start Df. In the Start Df box, enter the starting value of degrees of freedom used in the Power vs. Df, Power vs. Df1, and Power vs. Df2 power charts.

End Df. In the End Df box, enter  the final value of degrees of freedom used in the Power vs. Df, Power vs. Df1, and Power vs. Df2 power charts.

Start Ratio. In the Start Ratio box, enter the starting value of ratio used in the Power vs. Ratio power chart.

End Ratio. In the End Ratio box, enter the final value of ratio used in the Power vs. Ratio power chart.

Start Alpha. In the Start Alpha box, enter the starting value of alpha used in the Power vs. Alpha power chart.

End Alpha. In the End Alpha box, enter the final value of alpha used in the Power vs. Alpha power chart.

No. of Steps. In the No. of Steps box, enter the number of steps, or intervals, plotted on the X-axis in the power charts specified in the Power Charts box.

Power Charts. Use the buttons under Power Charts to produce charts of power as a function of degrees of freedom, ratio of population variances, or type I error rate. The range of values plotted on the X-axis, and the number of steps plotted, are controlled by parameters in the X-Axis Graphing Parameters box.  

Power vs. Df. Click the Power vs. Df button to produce a plot of power versus the number of degrees of freedom for the test, where both degrees of freedom, for numerator and denominator, are assumed to be equal.

Power vs. Df1. Click the Power vs. Df1 button to produce a plot of power versus the number of degrees of freedom for the test, where Df1, the degrees of freedom associated with the estimate of the variance for the first population, is varied while Df2, the degrees of freedom associated with the estimate of the variance for the second population, is held constant at its current fixed parameter value.

Power vs. Df2. Click the Power vs. Df2 button to produce a plot of power versus the number of degrees of freedom for the test, where Df2, the degrees of freedom associated with the estimate of the variance for the second population, is varied while Df1, the degrees of freedom associated with the estimate of the variance for the first population, is held constant at its current fixed parameter value.

Power vs. Ratio. Click the Power vs. Ratio button to produce a plot of power versus the ratio of the first population variance divided by the second.

Power vs. Alpha. Click the Power vs. Alpha button to produce a plot of power vs. type I error rate (α).