The explanation is in ?boxplot.stats (as the help for boxplot states).
Details:
The two ‘hinges’ are versions of the first and third quartile,
i.e., close to ‘quantile(x, c(1,3)/4)’. The hinges equal the
quartiles for odd n (where ‘n <- length(x)’) and differ for even
n. Whereas the quartiles only equal observations for ‘n %% 4 ==
1’ (n = 1 mod 4), the hinges do so _additionally_ for ‘n %% 4 ==
2’ (n = 2 mod 4), and are in the middle of two observations
otherwise.
And so on, with references.
Sarah
2012/1/13 René Brinkhuis <rene.brinkh...@live.nl>:
>
> Hi,
>
> I have a simple question about quartiles in R, especially how they are
> calculated using the boxplot.
> Quartiles
> (.25 and .75) in boxplot are different from the summary function and
> also don't match with the 9 types in the quantile function.
> See attachment for details.
> Can you give me the details on how the boxplot function does calculate these
> values?
>
> Cheers,
> Rene Brinkhuis (Netherlands)
--
Sarah Goslee
http://www.functionaldiversity.org
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