A Markov-chain method for computing the run-length distribution of the self-starting cumulative sum scheme

We propose an analytic method for computing the run-length distribution of the cumulative sum (CUSUM) of Q statistics. The method is based on a model in which the operation of this CUSUM is embedded in a nonstationary, discrete-time Markov chain. The calculations of the method agree closely with those of Monte Carlo simulation, supporting the method's accuracy. Our results facilitate understanding the effectiveness of the CUSUM of Q statistics in detecting process mean shifts.