Abstract
We introduce the t
0
-increasing failure rate (IFR-t
0
) class, where the failure rate at age x+t
0
is greater then or equal to the failure rate at age x for x≥0. The dual class of t
0
- decreasing failure rate (DER-t
0
) is defined analogoualy.The relation between the IFR -t
0
class and other classes of life distributions is studied. Preservation and nonpreservation properties of the IFR-t
0
and the DFR-t
0
classes under various reliablity operation are presented. The concet of stochastic comparison is utilized to cheracterized the IFR-t
0
class and to suggest other classes of life distributions for aging.