Distribution-free synthetic and runs-rules control charts combined with a Mann-Whitney chart

Control chart is one of the most important tools used in statistical process control and monitoring (SPCM) to detect changes in quality characteristics. This paper investigates the performance of the improved modified distribution-free synthetic and runs-rules charts combined with a Mann-Whitney (MW) chart, in terms of the average run length (ARL) and median run length (MRL) through intensive simulation. It is observed that the newly proposed improved modified synthetic and runs-rules MW charts present very attractive run-length properties and outperform the competing charts under non-normal underlying distributions. Numerical examples are given as illustration of the design and implementation of the proposed charts.