Also know as Tolerance limits.

Usage of tolerance intervals

Tolerance intervals are related to engineering tolerances limits. Typically, engineering tolerance limits define the maximum and minimum values for a product to work correctly. Engineering tolerance limits may be specified via Geometric Dimensioning and Tolerancing. Tolerance intervals are fundamental to control charts of various types. Statistical tolerance intervals (or limits) are derived from process data. These intervals quantify the variation manifest by the process. They define the capability of the process by specifiying minumum and maximum values. These values bound a region that contains a certain proportion of the total population with a specified probablity or confidence.

External References

See The NIST/SEMATECH e-Handbook of Statistical Methods (http://www.itl.nist.gov/div898/handbook/index.htm), 2004 July 17.

In particular Section 7.2.6.3 - Tolerance intervals for a normal distribution (http://www.itl.nist.gov/div898/handbook/prc/section2/prc263.htm)

See "Quality Control Handbook", Juran.