“…The simplest relation is obtained when upper and lower schemes do not interact-that is, if every realization of the process of observations has the property that, at the point where the upper scheme signals, the lower scheme is necessarily 0 and vice versa. Under the preceding assumptions, one obtains the ARL of the two-sided scheme in terms of its one-sided counterparts by using the classic formula due to Kemp (1961 If the noninteraction condition is satisfied, the preceding relation for the ARL remains valid for processes with serial correlation, provided that the RL is interpreted in the following way: Both upper and lower schemes are set to 0 after a signal produced by the process {Xi} that has reached a steady state, and the RL represents the number of observations taken from this moment until an out-of-control signal is produced. To see why this is true, let us perform the following experiment based on a single realization of the process {X,>, starting from the steady state: (a) Run upper and lower schemes in parallel.…”