Measuring process yield by fuzzy lower confidence bounds

Process yield is one standard numerical measure of process performance in manufacturing industry. Index S_PK has provided an exact measure of process yield. Most studies on estimating S_PK are based on crisp estimates involving precise output process measurements. However, measurements of product quality sometimes cannot be precisely recorded or collected. Hence, this study provides the fuzzy lower confidence bound for S_PK. The result helps the practitioners to make reliable decisions under fuzzy environment.