Calculating Required Sample Size

Select the Quick tab of the Multiple R²: Sample Size Calculation Results dialog box to access options to interactively view the results of sample size calculations.

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 Sample Size Charts.

Start Power. In the Start
Power box, enter the starting value of power goal used in the N
vs. Power

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

Start P². In the Start P² box, enter the starting value of P² used in the N vs. P² sample size chart.

End P². In the End P² box, enter the final value of P² used in the N vs. P² sample size chart.

Start Alpha. In the Start Alpha box, enter the starting value of alpha used in the N vs. Alpha sample size chart.

End Alpha. In the End Alpha box, enter the final value of alpha used in the N vs. Alpha sample size 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 Sample Size Charts box

Computing Algorithm. The Power Analysis module allows you to choose from two algorithms:

Faster.

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.

Sample Size Charts. Use the buttons under Sample Size Charts to produce charts of required N as a function of power goal, population squared multiple correlation, or type I error rate. Note that parameters given in the X-Axis Graphing Parameters group box control the range of values plotted on the X-axis and the number of steps plotted.

N vs. P². Click the N vs. P² button to produce a plot of sample size vs. P².

N vs. Alpha. Click the N vs. Alpha button to produce a plot of sample size (N) vs. type I error rate.

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