Look at ?quantile, especially the detail section on "type" and the second reference (and the see also section). There are many different definitions of quantiles/quartiles and different functions use different versions.
-- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.s...@imail.org 801.408.8111 > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] On Behalf Of Lewis Berman > Sent: Thursday, February 24, 2011 8:38 AM > To: r-help@R-project.org > Subject: [R] Boxplot not doing what I think it should > > My box plot below is drawing its upper whisker all the way to the last > point, instead of showing the point as an outlier. Am I > misunderstanding, or is it a bug? > > Help(boxplot) states for the parameter "range" that "this determines > how far the plot whiskers extend out from the box. If range is > positive, the whiskers extend to the most extreme data point which is > no more than range times the interquartile range from the box. A value > of zero causes the whiskers to extend to the data extremes." > > To my understanding, the code below, which drew the boxplot, should > have drawn the right-hand whisker only to 387 and shown 496 as an > outlier point. But it didn't. Using a range of 1.3 does. Horizontal > versus vertical does not matter. > > Also, the right edge of the box does not show the same 3rd Quartile as > does "summary." Explain, please. > > > > sort(t5g24times) > [1] 111 135 201 234 283 283 284 285 300 370 387 496 > > summary(t5g24times) > Min. 1st Qu. Median Mean 3rd Qu. Max. > 111.0 225.8 283.5 280.8 317.5 496.0 > > iqr <- 317.5 - 225.8 > > iqr > [1] 91.7 > > 317.5 + 1.5 * iqr > [1] 455.05 > > pdf() > > boxplot(c(t5g24times), horizontal=1, range=1.5) > > > R version info: > platform x86_64-apple-darwin9.8.0 > arch x86_64 > os darwin9.8.0 > system x86_64, darwin9.8.0 > status > major 2 > minor 12.0 > year 2010 > month 10 > day 15 > svn rev 53317 > language R > version.string R version 2.12.0 (2010-10-15) ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.