# Overview for Power and Sample Size for 2 Proportions

Use Power and Sample Size for 2 Proportions to examine the relationship between power, sample size, and the comparison proportion when you want to compare the difference between two population proportions. These calculations require that your data contain only two categories, such as pass/fail. Use these calculations for the following reasons:
• Before you collect data for a 2 proportions test, to ensure that your test has an adequate sample size to achieve acceptable power
• After a 2 proportions test, to improve the design for the next test

For example, a university financial aid officer wants to determine whether male or female students are more likely to get a job in the summer. Before collecting the data for a 2 proportions test, the officer uses a power and sample size calculation to determine how small of a difference the test can detect with the desired sample size and power.

## Where to find this analysis

To perform a power and sample size calculation for a 2 proportions test, choose Stat > Power and Sample Size > 2 Proportions.

## When to use an alternate analysis

If your data contain counts, such as the number of defects per unit, use Power and Sample Size for 2-Sample Poisson Rate. For more information on data types, go to Data types you can analyze with a hypothesis test.