Using the Grubbs and Cochran tests to identify outliers
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Updated: Nov 5, 2025

Competitive Genomic Screens of Barcoded Yeast Libraries
Published on: August 11, 2011
Abstract:
In a previous Technical Brief (TB No. 39) three approaches for tackling suspect results were summarised. Median-based and robust methods respectively ignore and down-weight measurements at the extremes of a data set, while significance tests can be used to decide if suspect measurements can be rejected as outliers. This last approach is perhaps still the most popular one, and is used in several standards, despite possible drawbacks. Here significance testing for identifying outliers is considered in more detail with the aid of some typical examples.
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Quantifying and Rejecting Outliers: The Grubbs Test
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What Are Outliers?
The z score is used to find outliers or unusual values. It should be noted that any values beyond -2 and +2 are...
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