가중표준편차를 이용한 가변표본채취간격 x관리도

This article proposes a variable sampling interval (VSI) - X control chart using weighted standard deviation (WSD)method for skewed populations. The WSD method decomposes the standard deviation of a quality characteristic intoupper and lower deviations and adjusts control limits and warning limits of a control chart in accordance with thedirection and degree of skewness. A control chart constant is derived for estimating the standard deviation of skeweddistributions with the mean of sample standard deviations. The proposed chart is compared with the conventionalVSI - X control chart under some skewed distributions. Simulation study shows that the proposed WSD VSI chart cancontrol the in-control average time to signal (ATS) as an adequate level better than the conventional VSI chart, andthe proposed chart can detect a decrease in the process mean of a quality characteristic following a positively skeweddistribution more quickly than the standard VSI chart.