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.
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