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Topic: boxplot outliers
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Paul Velleman

Posts: 1,607
Registered: 12/6/04
boxplot outliers
Posted: Sep 2, 1996 11:04 PM
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Lisa Winer asks:
>
>First of all, does anyone know why it is customary to multiply 1.5*IQR in
>order to find outliers? In particular, why is it 1.5 and not, for example,
>2?
>


The "official" answer from John Tukey (when I asked) is:
because 1 is too small and 2 is too large.

There is a paper by Hoaglin and Ygelevich (sp?) in which they did some
simulations and showed that the outlier rule is really quite good across a
pretty wide array of distributions. I don't know the full reference.

-- Paul Velleman







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