Use Power and
Sample Size for 2-Sample t to examine the relationship between power, sample size, and the difference when you want to compare the difference between two population means. Use these calculations for the following reasons:

- Before you collect data for a 2-sample t-test, to ensure that your test has an adequate sample size to achieve acceptable power
- After a 2-sample t-test, to improve the design for the next test

For example, a healthcare consultant wants to compare the mean patient satisfaction ratings of two hospitals. Before collecting the data for a 2-sample t-test, the consultant uses a power and sample size calculation to determine how large the sample must be to detect a difference between the means of the two ratings with an 90% probability (power 0.9).

To perform a power and sample size calculation for a 2-sample t-test, choose

.If you have paired or dependent data, such as measurements of a bearing taken with two different calipers, use Power and Sample Size for Paired t instead. For more information, go to How are dependent and independent samples different?.