A Product Quality Index Derived from Product Lifetime Distribution

The reliability requirement of a product (or component) is often given by the mean life. Actually, the expected service life of a product is smaller than the mean life unless the product is run to failure. This implies that ana- fractile life with 0 < alpha << 0.5 can better represent the product service lifetime than the mean life. On the other hand, the life of about 50% of the products is larger than the mean life. As such, the (1-alpha)-fractile lifetime reflects the lifetime of the quality products, and can be viewed as a goal for most of the products to achieve by improvement of the product quality. A product quality index is defined by combining these two lifetime measures. The quality indices associated with several well-known lifetime distributions are derived as functions of some distributional parameter(s). The proposed index represents the life consistence of the products produced in batches and can be used for evaluating and comparing the quality of the products produced by different manufacturers. The usefulness of the quality index is illustrated by an example.