It's just rounding errors. 60 is exactly 1.5x the IQR from 78.
Look at the whole output:
$stats
[1] 60 78 80 90 100
$n
[1] 18
$conf
[1] 75.53109 84.46891
$out
[1] 50 120 39 140
vs
$stats
[1] 7.8 7.8 8.0 9.0 10.0
$n
[1] 18
$conf
[1] 7.553109 8.446891
$out
[1] 5.0 12.0 6.0 3.9 14.0
Given that a point is sitting exactly on the boundary, it's arbitrary
whether it gets put inside or outside, and decided by rounding errors.
On Tue, 25 Sep 2001, Trenkler, Dietrich wrote:
> Is this a bug?
No.
>
> >"xx" <- c(50, 79, 120, 78, 90, 100, 78, 80,
> + 90, 80, 60, 39, 90, 85, 140, 100, 80, 80)
> > boxplot.stats(xx)$stats
> [1] 60 78 80 90 100
> > boxplot.stats(0.1*xx)$stats
> [1] 7.8 7.8 8.0 9.0 10.0
>
> I suppose the way the numbers in 0.1*xx are internally stored may
> cause this problem:
>
> > formatC(0.1*xx[2],format="f",digits=16)
> [1] "7.9000000000000004"
>
> Version:
> platform = i386-pc-mingw32
> arch = x86
> os = Win32
> system = x86, Win32
> status > major = 1
> minor = 3.1
> year = 2001
> month = 08
> day = 31
> language = R
>
> Windows NT 4.0 (build 1381) Service Pack 6
>
> --- D.Trenkler ---
>
>
****************************************************************************
> *****
> Dr. Dietrich Trenkler (dtrenkler at nts6.oec.uni-osnabrueck.de)
> Statistik / Empirische Wirtschaftsforschung
> Universitaet Osnabrueck
> Rolandstrasse 8 Phone: +49(0)
541-969-2753
> D-49069 Osnabrueck Fax : +49(0) 541-969-2744
> GERMANY
>
****************************************************************************
> *****
>
>
>
>
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--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
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