Estimating Reliability Growth

Test programs are conducted to identify system failure modes and to estimate reliability. If the system can be changed so that some of the identified failure modes are eliminated and new failure modes are not introduced, the reliability of the system is improved. This paper examines small-sample techniques for estimating the change in reliability without the benefit of test data from the improved system. A decision to make the improvements can be based on the estimated increase in reliability. The procedures used for estimating changes can also be adapted to estimating reliability using data from a test program conducted in stages. For this case, a sample is taken at each stage and changes are made so that all newly identified failure modes which are correctable are eliminated from the system. Simulation is used to study reliability estimators both when just one sample is taken and when sampling is conducted in stages.