“…Exact computation of the performance measures, such as the average run length, average detection delay, and false alarm probability, is rarely achieved. Contrary to the continuous-time model, where analytical tools such as martingale methods and Itô calculus are available (see, e.g., [19,41,42]), exact computation of the first passage identities for discrete-time processes tends to be infeasible by traditional methods. For this reason, research on the CUSUM statistic, which is a discrete-time process, has focused on pursuing approximate results.…”