One inherent weakness of the nonparametric control charts is that the signaling events are not independent and therefore the
ARK of the chart can not be calculated as the reciprocal of the signaling probability . However,one can make use of an appropriate
conditioning argument(see Chakraborty, 2000) to establish a formula for the exact run length distribution and its mean.
In view of (4) and (5)it's clear that , under the condition Xa:b = (xa, xa+1, ..., xb) = xa:b ∈ Rb−a+1, the waiting time random
variable N which describes the number of Y-samples until out-of-control alarm issued follows geometric distribution with
success probability