Wasserman, Gary S.; Wadsworth, Harrison M. (1989, ASQC and the American Statistical Association) Wayne State University, Detroit, MI; Georgia Institute of Technology, Atlanta, GA
Beattie (1962) devised a continuous process-monitoring procedure that does not require 100% inspection. The procedure is a composite of two cumulative sum procedures. He considered the case in which the variate under observation is discrete. Here we extend Beattie's procedure to monitor a process when the observed variate is normally distributed. Additionally, we show how this procedure can be used to monitor two-sided variations of the parameter under observation. We use Wald's approximating expressions for the sequential probability ratio test to obtain an approximate operating characteristic (OC) curve for the procedure. We also evaluate the accuracy of the OC-curve expression and use it to develop design guidelines. Two examples demonstrate the simplicity of the design rules.
Continuous quality improvement (CQI),Cumulative sum control chart (CUSUM),Process control,Quality control (QC),SPRT