Further Study

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Analytical Sciences Digital Library

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Larger Data Sets

One limitation to our treatment of the outliers is that the Q-table is limited to data sets consisting of 3 to 10 samples. Q-tables are available for larger sample sizes, although, interestingly, the test as defined here is less reliable for samples larger than 10. There are alternative equations, which use different definitions for the gap and range. For details, consult the following paper:

Rorabacher, D. B. Anal. Chem. 1991, 63, 139-146.

Multiple Outliers

Suppose your data set has an apparent outlier on each end or two apparent outliers on one end. For small data sets, the Q-test as defined will be unable to detect an outlier. For larger data sets, those containing more than 11 samples, there are alternative forms of the Q-test that provides some discriminating ability. For details, consult the following paper:

Rorabacher, D. B. Anal. Chem. 1991, 63, 139-146.