Calculating Required Sample Size

Select the Quick
tab of the Two
Variances: Sample Size Calculation Results dialog box to access options
to interactively view the results of sample size calculations and generate
plots of required sample size as a function of quantities that affect
sample size 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 Sample Size Charts.

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

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

Start Ratio. In the Start Ratio box, enter the starting value of ratio used in the Df vs. Ratio sample size chart.

End Ratio. In the End Ratio box, enter the final value of ratio used in the Df vs. Ratio sample size chart.

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

End Alpha. In the End Alpha box, enter the final value of alpha used in the Df 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.

Sample Size Charts.
Use the buttons under Sample
Size Charts to produce charts of required degrees of freedom as
a function of power goal, 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.

Df vs. Ratio. Click the Df vs. Ratio button to produce a plot of degrees of freedom (Df) versus population variance (Var).

Df vs. Alpha. Click the Df. vs. Alpha button to produce a plot of degrees of freedom (Df) vs. type I error rate.

Df vs. Power. Click the Df vs. Power button to produce a plot of degrees of freedom (Df) versus power goal.