On the Choice of a Capability Index for Asymmetric Tolerances

Abstract

For a process normally distributed and a target located at the midpoint of a two-sided tolerance interval, Vannman [10] suggests a family of indices depending on two parameters. In order to choose the parameters for obtaining an index that is sensitive to departures of the mean from the target, Vannman takes the properties of its estimator into account. For a target not located at the midpoint of the tolerance interval, Chen and Pearn [2] suggest a family of indices generalizing Vannman’s. The moments of the estimators of these indices are studied to choose an index whose the estimator is sensitive to departures of the mean from the target, and has a small bias, and a small mean square error.

Key Words:

• Asymmetric tolerances
• capability indices
• estimation

Additional information

Notes on contributors

Daniel Grau

Daniel Grau is an Associate Professor in Statistics in University of Pau in the Business/Management Department as well as the Statistics Department. His research interests concern quality control.