Life expectancy for a class of life distributions having the "setting the clock back to zero" property

It is demonstrated that the expression for the life expectancy of an individual in biomedical investigations can be greatly simplified if the class of life distributions possesses what has been called the "setting the clock back to zero" property, studied previously by Raja Rao and Talwalker. It is shown that the Gompertzian growth process, Krane's family of life distributions, and the linear hazard exponential distribution have this property. To illustrate the use of this property, an individual's life expectancy is tabulated for several choices of the parameter values when the individual's life distribution belongs to a Gompertzian growth process. In addition, it is shown that a new survival model considered by Chiang and Conforti for the estimation of time to tumor has the "setting the clock back to zero" property. Its life expectancy is evaluated at any given time chi 0 using this property.