CONFIDENCE-BOUNDS FOR CAPABILITY INDEXES

Capability indices compare the actual performance of a manufacturing process to the desired performance. In practice these indices are estimated using sample data, often with quite small sample sizes. Thus, it is of interest to obtain confidence limits (in particular, lower bounds) for the actual capability index given a sample estimate. Several methods for computing lower confidence bounds for these indices are described. A geometric view of the problem is presented and used as a basis for evaluating the performance of the various methods.