Complete the following steps to interpret Sample Size for Tolerance Intervals. Key output includes the sample size, the margin of error, and the confidence levels and achieved confidence levels.

If you specify one or more values for the maximum acceptable percentages of the population in the interval, Minitab calculates the sample sizes that are required to achieve those percentages.

A more precise tolerance interval is more useful and more informative, but smaller margins of error (calculated as maximum percentage of population in interval − minimum percentage of population in interval) require larger sample sizes. If a tolerance interval is not sufficiently precise, it can be too wide and include a much larger percentage of the population than you specify.

Suppose that p is the targeted minimum percentage of the population for a tolerance interval. The following statistics define the precision of the tolerance interval:

- Maximum acceptable percentage of population in interval (P*)
- The percentage of the population greater than the desired p that might be included in the interval.
- Probability the population coverage exceeds p*
- The probability that the interval contains more of the population than p*.
- Common values for the margin of error probability include 0.01, 0.05, and 0.1. Larger values for the margin of error probability can result in a tolerance interval that covers a much larger percentage of the population than the target, p*.

If you specify one or more sample sizes, Minitab calculates the maximum acceptable percentages of the population in the interval that you can achieve with those sample sizes. Minitab performs calculations for the normal and the nonparametric method. For calculations for other distributions, use Tolerance Intervals (Nonnormal Distribution).

Increasing the sample size decreases the maximum acceptable percentages of the population in the interval. If a tolerance interval is not sufficiently precise, it can be too wide and include a much larger percentage of the population than you specify.