A generally weighted moving average signed-rank control chart

Abstract

The idea of process monitoring emerged so as to preserve and improve the quality of a manufacturing process. In this regard, control charts are widely accepted tools in the manufacturing sector for monitoring the quality of a process. However, a specific distributional assumption for any process is restrictive and often criticised. Distribution-free control charts are efficient alternatives when information on the process distribution is partially or completely unavailable. In this article, we propose a distribution-free generally weighted moving average (GWMA) control chart based on the Wilcoxon signed-rank (SR) statistic. Extensive simulation is done to study the performance of the proposed chart. The performance of the proposed chart is then compared to a number of existing control charts including the parametric GWMA chart for subgroup averages, a recently proposed GWMA chart based on the sign statistic and an exponentially weighted moving average (EWMA) chart based on the signed-rank statistic. The simulation results reveal that the proposed chart performs just as well and in many cases better than the existing charts, and therefore can serve as a useful alternative in practice.