Nonparametric Shewhart-Type Signed-Rank Control Chart with Variable Sampling Interval

Nonparametric control chart based on signed-rank statistic is used for detecting changes in mean (median). Although the Sign-Rank (SR) chart is more efficient under heavy-tailed distributions (double exponential and Cauchy) but the performance of this chart is very inappropriate in light-tailed distributions (uniform and normal). In this paper, signed-rank chart is developed with variable sampling interval. The performance of signed-rank chart with variable sampling interval (VSI-SR) is compared to signed-rank chart with fixed sampling interval (FSI-SR) and chart. The numerical results demonstrated the VSI-SR chart is better from the FSI-SR chart. Also the VSI SR chart is more efficient from chart in heavy-tailed distributions and some of changes under normal light-tailed distribution.