The Two Sample Proportions option computes the power or sample sizes needed to detect the difference between two proportions, p1 and p2.
where p1 and p2 are the population proportions from two populations, and D0 is the hypothesized difference in proportions.
is the proportion difference (D0) to test against, or is left blank for computation. The default value is 0.2.
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1.

2.

Click Two Sample Proportions.

3.

Accept the default value of Alpha as 0.05.

4.

Enter 0.08 for Proportion 1.

5.

Enter 0.06 for Proportion 2.

6.

Accept the default option of TwoSided.

7.

Enter 0.0 for Null Difference in Proportion.

8.

Enter 0.8 for Power.

9.

10.

Click Continue.

The Sample Size window shows sample sizes of 2554. (see Difference Between Two Proportions for a TwoSided Test.) Testing for a onesided test is conducted similarly. Simply select the OneSided option.
1.

2.

Click Two Sample Proportions.

3.

Accept the default value of Alpha as 0.05.

4.

Enter 0.6 for Proportion 1.

5.

Enter 0.5 for Proportion 2.

6.

Select OneSided.

7.

Enter 0.01 as the Null Difference in Proportion.

8.

Enter 400 for Sample Size 1.

9.

Enter 400 for Sample Size 2.

10.

Leave Power blank.

11.

Click Continue.

Difference Between Two Proportions for a OneSided Test shows the Two Proportions windows with the estimated Power calculation of 0.82.