While an XmR chart is commonly used as a process behavior chart, it may also be used as a test of homogeneity for a finite number of values. This column explains the difference in these two uses of the XmR chart and compares the homogeneity chart with the W-ratio test, which I presented in my June column, Analysis Using Few Data, Part 1. In addition, this column contains an expanded table of critical values for the W-ratio test.

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