Variance reduction in aged sample data by the use of lot acceptance test data [missile primary cell testing]

NAVSEA Crane Division performs ongoing quality evaluation test (QET) programs to evaluate the steady deterioration with age of critical performance parameters (such as risetime and runtime) of Navy Fleet-aged missile primary batteries. The goal is to estimate service life (SL), the age at which these batteries must be replaced. QET data is obtained by sampling a few dozen units of various ages throughout the range of date of manufacturing (DOM) of the inventory. It is expensive to obtain; few data points are available. Typically, a QET is performed every 3-5 years on 22 samples. Abundant lot acceptance test (LAT) data usually is available; it is used to perform lot sentencing (accept or reject) before shipping. Here, the authors show new mathematical methods which improve the accuracy of service life estimation, and which also may be a significant advance in the general mathematical theory of regression analysis. The enhanced delta method also eliminates the well-known problem that arises when QET and LAT raw data sets are combined in one analysis