Explain why rational subgrouping should be used in

Step 1 of 3

Samples whose size and frequency have been designed to make it likely that process

changes will occur between, rather than within, the samples are referred to as rational

subgroups.

Rational Subgrouping Strategy

The samples (rational subgroups) should be chosen in a manner that

     1.  Gives the maximum chance for the measurements in each sample to be similar

          (i.e., to be affected by the same sources of variation)

     2.  Gives the maximum chance for the samples to differ (i.e., be affected by at least

          one different source of variation)