Evaluation of a three-state adaptive sample size X 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 threestate 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 threestate adaptive control chart schemes are gained without increasing the average incontrol 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.