In last month’s article, “ANOVA and the Process Behavior Chart,” we saw how both techniques use the same basic comparison to answer completely different questions. Here, we’ll look at a case history where both techniques were used.

A physical property of a mass-produced item was important to its functionality. The production of these items involved three steps: batches of compound were mixed, molded into parts, and coated. In an effort to maximize a product characteristic, an experiment involving three production variables was carried out. Factor A was studied at two levels; Factor B was studied at three levels; and Factor C was studied at five levels. So the fully crossed study required 30 experimental runs. For each run, a sample of 40 parts was selected from the output and each part was measured. Thus the manufacturer had 30 treatments with 40 observations per treatment for a total of 1,200 observations.

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