table 6.7 contains data on mortgage application processing costs for weeks 21-40 there data plotted in figure 6.20 on the continuation of the control chart for individual and the moving range control chart developed in example 6.5 as this figure makes clear an upward shift in cost has occurred around week 39 since there is an obvious sift in process level pattern on the chart for individual followed by another out of control signal at week 40 not that the moving range chart also reacts to this level shift with a single large spike at week 39 this spike on the moving range chart is sometime helpful in identifying exactly where a process shift in the mean has occurred clearly one should look for possible assignable causes around weeks 39 possible causes could include an unusual number of applications requiring additional manual underwriting work or possibly new underwriters working in the process or possible temporary underwriters replacing regular employees taking vacations