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282 Part IV: Quality Assurance
Continued
Table 19.6
Number of nonconforming computer chips with different size samples
inspected each day during the study period of 30 days.
Part IV.B.4
Number of
Number of
nonconforming
nonconforming
Day x Sample size Day x Sample size
1 7 908 16 7 962
2 11 986 17 11 926
3 8 976 18 7 917
4 7 991 19 9 978
5 7 944 20 7 961
6 5 906 21 6 970
7 11 928 22 9 905
8 5 948 23 9 962
9 10 994 24 8 900
10 8 960 25 11 998
11 7 982 26 5 935
12 6 921 27 6 970
13 7 938 28 6 967
14 10 1000 29 9 983
15 6 982 30 8 976
Thus, the p chart for the data in Table 19.6 is as shown in Figure 19.11.
From Figure 19.11 we see that all of the points are well within the control limits and
that there is no apparent pattern or trend in the chart. Thus, the process is stable. Also,
note that in Figure 19.10 we have a run of seven points that fall below the center line
whereas in Figure 19.11 there is no such run even though we are dealing with the same
process. Such differences are normal when samples are taken at different times.
Continued