LOWER CONFIDENCE BOUND ON THE PERCENTAGE IMPROVEMENT IN COMPARING 2 FAILURE RATES

It is often necessary to determine whether a design change in a product has actually improved its failure rate, and to compute a lower confidence bound on the percentage of failure rate improvement affected by the change. This paper shows how such a bound can be computed based on certain test data. The main result of the paper is a special case of an equivalent result derived in Lehmann for hypothesis testing and used extensively in applied statistics. However, ft is not well-known in its confidence interval form, nor is it extensively reported in reliability methods books, and its derivation is important in reliability testing.