International Journal of Industrial Engineering & Production Management

Nonparametric control chart based on rank is used for detecting changes in median(mean). In this article ,Signed-rank control chart is considered with variable sampling interval. We compared the performance of Signed-rank with variable sampling interval (VSI-SR) to Signed-rank with Fixed Sampling interval (FSI-SR),the numerical results demonstrated the VSI feature is so useful. Bakir[1] showed SR chart is more efficient under heavy-tailed distributions than its parametric equivalent x-bar chart. This article include comparisons between VSI-SR and FSI x ̅ chart under light tailed distributions(the uniform and the normal) and heavy- tailed distributions(the double exponential and the Cauchy). Using VSI feature makes SR chart more sensitive under light-tailed distributions so that it can compete with x-bar chart.