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A chemical company has collected 15 daily subgroups of measurements of an important chemical property called "acid value" for one of its products. Each subgroup consists of six acid value readings: a single reading was taken every four hours during the day, and the readings for a day are taken as a subgroup. The 15 daily subgroups are given in Table 17.8.
TABLE 17.8
15 Subgroups of Acid Value Measurements for a Chemical Process
b. Set up and R charts for the acid value data. Are these charts in statistical control?
c. On the basis of these charts, is it possible to draw proper conclusions about whether the mean acid value is changing? Explain why or why not.
f. Are the revised and R charts for the remaining 13 subgroups in statistical control? Explain. What does this result tell us to do? |
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