Combined Shewhart-CUSUM Quality Control Schemes

The Shewhart-CUSUM quality control scheme which combines the key features of the Shewhart and CUSUM control procedures is described and evaluated. In this scheme the CUSUM feature will quickly detect small shifts from the goal while the addition of Shewhart limits increases the speed of detecting large shifts. The combined Shewhart-CUSUM scheme has performance comparable to that of the more involved parabolic CUSUM. The Shewhart-CUSUM scheme works with only the current observations so it requires less computer storage space than parbolic CUSUM, which requires the storage of several previous observations. This becomes particularly important when many control schemes are simultaneously implemented.