Multiple R²: Power Calculation Results - Quick Tab

Calculating Power

Select the Quick tab of the Multiple R²: Power Calculation Results 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 N. In the Start N box, enter the starting value of N used in the Power vs. N power chart.

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

Start P². In the Start P² box, enter the starting value of P² used in the Power vs. P² power chart.

End P². In the End P² box, enter the final value of P² used in the Power vs. P² 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.

Computing Algorithm. In the Power Analysis module, you can choose from two algorithms:

Faster.  Select the Faster option button to employ Lee's (1971, p. 123) non-central F approximation. This approximation is accurate to about four decimal places, and is satisfactory for most applications.

More Accurate. Select the Most Accurate option button to perform a slower, but more accurate calculation, based on theory described in Lee (1972), typically exact to at least five decimal places.

Power Charts. Use the buttons under Power Charts to produce charts of power as a function of variables known to affect it. Note that parameters specified under X-Axis Graphing Parameters control the range of values plotted on the X-axis and the number of steps plotted.

Power vs. N. Click the Power vs. N button to produce a plot of power versus sample size N.

Power vs. P². Click the Power vs. P² button to produce a plot of power vs. P².

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