Sequential order statistics (SOSs) have been introduced in as a generalization of (common) order statistics. A particular application of order statistics is located in reliability theory; the rth order statistic X r, n of an iid sample of random variables according to some distribution function F represents the life length of an ( n − r + 1)-out-of- n system, where all n components start working simultaneously, and the system operates as long as n − r + 1 components function, and it fails if r or more components fail ( r = 1 and r = n correspond to a series system and a parallel system of n components, respectively).