Using Confidence Intervals to Compare Process Capability Indices

Abstract

Process capability indices are widely used to measure process performance. In situations such as selecting a supplier and assessing process improvement, it is of interest to compare capability indices for two different processes or the same process before and after an adjustment. In this paper, we consider several methods for performing this comparison on the indices C_pk and C_pm . The methods are compared using a computer simulation. Recommendations are provided for selecting an appropriate method based on power and test size computations.

Keywords:

• Bonferroni method
• generalized confidence intervals