In the June 1991 issue of Quality Progress, Gunter presents several control charts. Four of these charts are reproduced in Figure 17.18. For each chart, tind any evidence of a lack of statistical control (that is, for each chart identify any evidence of the existence of one or more assignable causes). In each case, if such evidence exists, clearly explain why the plot points indicate that the process is not in control.
(a)

(b)

(c)

(d)

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UCL = 5.3 5.0 5 4.0 4.0 3.0 LCL = 2.7 -- 0 5 10 15 20 Subgroup number 5.0 4.0 3.0 LCL-2.7 5 10 15 20 Subgroup number UCL 5.3 5.0 5 4.0 x = 4.0 3.0 LCL 2.7 5 10 15 20 Subgroup number UCL= 5.3 5.0 E 2 4.0 LCL " 2.7 0 5 10 5 20 Subgroup number