The SPRT sign chart for process location

Abstract

This paper develops a nonparametric sequential probability ratio test (SPRT) control chart for monitoring the process location. The chart is based on a sequential sign test. Young’s algorithm to determine the properties of the SPRT for a parameter of discrete Koopman-Darmois density is used to obtain the exact statistical performance measures of the proposed chart. The proposed chart substantially outperforms the Shewhart sign, synthetic Shewhart sign, CUSUM sign, and EWMA sign charts in detecting a location shift of any size. It is a preferable alternative to the parametric SPRT chart for mean when the underlying process distribution is not precisely known. The implementation of the chart is illustrated through an example.