A new class of ageing distributions

The class of new worse/better than used in expectation on average (NWUEA/NBUEA) distributions is proposed. It is defined by the requirement that for each age t a weighted average of mean residual lives be greater/smaller than the life expectancy at birth. The weights are the shares of ages up to t in the steady state stock which results from cohorts whose density is to be classified. The NWUEA class has a second order stochastic dominance property whose first order counterpart defines the class of new worse than used in expectation (NWUE) distributions.