The Tolerance Intervals command analyzes a sample from a population, and calculates a range of values for a product's characteristic that likely covers a specified proportion of future product output. Alternatively, a lower or upper limit may be constructed such that the specified proportion will be greater than or less than the limit. Tolerance intervals specify both a population proportion and a confidence level. Manufacturers frequently use them to detect excessive variation by comparing client requirements to tolerance limits that cover an acceptable proportion of the population.

Minitab displays results using both the normal and nonparametric methods. See Normal and nonparametric methods for tolerance intervals for more details. Minitab uses an exact method to calculate the normal tolerance intervals.

A washer manufacturer is concerned about washer thickness variability. The manufacturer wants to see how the range of thickness values that 95% of all washers produced are likely to fall within compares to a major client's requirements. The analysts select a random sample of 100 washers and measure their thickness in millimeters.

Data: Washer.MTW (available in the Sample Data folder).