The deviation of process output is usually estimated through the range or deviation of the sub-samples in the calculation of Process Capability Index. There are autocorrelation in many practical process outputs. Based on several stationary stochastic process models of the time-series analysis, the impact of the sampling method, sub-sample sizes and deviation estimating methods in standard statistical process control are analyzed via simulation in process capability analysis. The necessity of autocorrelation testing of process and proper analysis procedure and methods are set up for these cases.
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