[R] Whiskers on the default boxplot {graphics}

Robert Baer rbaer at atsu.edu
Wed May 12 18:51:47 CEST 2010

----- Original Message ----- 

It would be great if the description could be modified to include the 
mysterious bit about the upper and lower bound whisker positions:

upper whisker = min(max(x), Q_3 + 1.5 * IQR)
lower whisker = max(min(x), Q_1 - 1.5 * IQR)

-- snip --
NOT quite!

The boxplot.stats help reads under the coef argument:
"... the whiskers extend to the most extreme data point which is no more 
than coef times the length of the box away from the box."

If there are outliers, and the most extreme data point within 1.5 *IQR of Q1 
or Q3 is less than 1.5 IQRs, and the wisker may "end earlier" than 1.5*IQR, 
but the data point at which it ends may NOT be max(x) or min(x).

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