Bootstrap confidence interval of the difference between two process capability indices

Abstract

The process capability index, C-pk, is extensively used to assess process performance in manufacturing industry. Statistical hypothesis testing or an interval estimation of a single C-pk had been derived under a normally distributed process. However, the difference between two process capabilily indices, C-pk1 - C-pk2, cannot be inferred statistically because of the complexily of the sampling probability theory. This study proposes a bootstrap resampling simulation method to construct the biased corrected percentile bootstrap (BCPB) confidence interval Of (C-pk1 - C-pk2), which can be used to select the better of two suppliers. The various simulation results indicate that the bootstrap confidence interval Of (C-pk1 - C-pk2) can be employed to evaluate effectively the difference between the performance of two suppliers.