Defining the Decision Interval for a One-Sided Cusum Scheme
The height of the decision interval is 
, expressed as a multiple of the standard error of the subgroup mean. You can specify with the H= option in the XCHART statement or with the variable _H_ in a LIMITS= data set. The decision interval is displayed as a horizontal line on the cusum chart, as illustrated in Figure 6.13.
Figure 6.13
Decision Interval
Interpreting One-Sided Cusum Charts
A shift or out-of-control condition is signaled at time 
if the cusum 
plotted at time exceeds the decision interval line.
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