Rational Subgroup

Rational Subgroup - A rational subgroup is a subset of data defined by a specific factor such as a stratifying factor or a time period. Rational subgrouping identifies and separates special cause variation (variation between subgroups caused by specific, identifiable factors.

[Category=Data Quality ]

Source: iSixSigma, 19 February 2011 11:54:09, https:web.archive.org/web/20111109014246/http:www.isixsigma.com/index.php?option=com_glossary

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Rational Subgroup - A rational subgroup is one in which the samples are selected so that the chance for variation due to special causes occurring within a subgroup is minimized, while the chance for special cause variation between subgroups is maximized. The key item to remember when developing a sampling plan is that the variation between subgroups is going to be compared to the variation within subgroups. Taking consecutive samples for the subgroups minimizes the opportunity for the process to change and should minimize the within-subgroup variation. The sampling frequency will determine the opportunity the process has to change between subgroups. The variation within a subgroup represents the piece-to-piece variation over a short period of time. Any significant variation between subgroups would reflect changes in the process that should be investigated for appropriate action. Source: AIAG SPC Manual.

[Category=Quality ]

Source: The Quality Portal, 21 April 2011 08:05:40, http://thequalityportal.com/glossary/l.htm