Abstract
Quantities defined to describe the aging phenomenon in lifetime studies include the specific aging factor', 'hazard rate average' and 'mean' residual lifetime'. But for different distributions the expressions for these quantities will be different and in some cases there are only approximate asymptotic expressions for their computation and it may not be so simple to calculate them. As any univariate continuous distribution can be approximated by a member of the Generalized Lambda Distribution (GLD) family, using GLD it is easy to find out single unified expressions for these quantities of all non negative univariate continuous distributions and thus unified expressions for the criteria of aging.