Assessing process performance based on the incapability index C _pp

Process incapability index C_pp has been introduced to the manufacturing industry to measure process performance. But all existing methods for testing C_pp require further estimation of the distribution parameters when calculating the p-values and critical values causing additional sampling errors, which is unreliable. In this paper, an efficient SAS computer program is provided to calculate the p-values. Extensive calculations were performed to examine the behavior of the p-values and the critical values c ₀ against the distribution parameter. Useful critical values for commonly used capability requirements are also tabulated. A simple but practical step-by-step hypothesis-testing procedure is developed for in-plant applications.