# Overview for Power and Sample Size for 1-Sample t

Use Power and Sample Size for 1-Sample t to examine the relationship between power, sample size, and the difference when you want to compare the mean of a population to a target or reference value. These calculations do not require you to know the standard deviation of the population. Use these calculations for the following reasons:
• Before you collect data for a 1-sample t-test, to ensure that your test has an adequate sample size to achieve acceptable power
• After a 1-sample t-test, to improve the design for the next test

For example, a quality analyst wants to determine whether the mean thread length of bolts meets the target of 20 mm. Before collecting the data for a 1-sample t-test, the analyst uses a power and sample size calculation to determine how large the sample must be to obtain a power of 80% (0.8).

## Where to find this analysis

To perform a power and sample size calculation for a 1-sample t-test, choose Stat > Power and Sample Size > 1-Sample t.

## When to use an alternate analysis

If you know the standard deviation of the population, use Power and Sample Size for 1-Sample Z because the Z-test has more power than the t-test.