Evaluation of a three-state adaptive sample size (X)over-bar control chart

A three-state adaptive sample size control chart is developed and its performance is compared with the standard Shewhart control chart and a two-state adaptive sample size control chart. In general, significant improvements in shift detection capability results from using an adaptive sample size control chart, and the three-state adaptive control chart is superior to the two-state adaptive control for small shifts in the process mean. The improvements found in the two-state and three-state adaptive control chart schemes are gained without increasing the average in-control sample size over the standard non-adaptive Shewhart control chart. The three-state procedure is only slightly better than the two-state scheme, and so the two-state scheme is likely adequate in most applications. The three process monitoring techniques are compared using both steady-state and start-up cases.