Abstract
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. © 2010 IEEE.