Cusum

Abstract

Optimum cumulative sum control charts for location and shape parameters of the IG distribution have been suggested by Hawkins and Olwell(1997) and these charts are used for detecting step changes in both parameters. These authors have also examined a data set which involves the task completion times of crews of workers at a General Motors Plant in Oshawa,Ontario,first considered by Desmond and Chapman(1993). One example involved data which had been well modelled by an inverse Gaussian law. Increases in the mean μ or decreases in λ will tend to decrease the service rate and cause a slowdown in the overall process in an assembly line. On the other hand a decrease in μ and increase in λs allows the management in determining factors that will help in improving service rates and diminish the variation. This is a typical example of the Cusum chart at work.