Schaefer, Robert L. Dr. <schaefrl <at> muohio.edu> writes: > I've just started using R and am still a neophyte, but I found the following curious result. I'm using the > current version of R (2.5.1 (2007-06-27) ). > > Why are the results for the third quartile different in the output from the summary and fivenum commands? > For the following data set > > 457 514 530 530 538 560 687 745 745 778 786 790 792 821 821 822 822 > 828 845 850 886 886 886 913 1050 1050 1065 1065 1065 1065 1090 1130 > > Summary yields: > > Min. 1st Qu. Median Mean 3rd Qu. Max. > 457.0 745.0 822.0 825.4 947.2 1130.0 > > While fivenum yields: > > [1] 457.0 745.0 822.0 981.5 1130.0 > > The third quartile is being correctly calculated in the fivenum command and incorrectly in the summary command. > > Bob
If you look in ?boxplot.stats, it says: 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. Where 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. I got here by looking a summary.default and seeing that it uses the quantile function and then looking at fivenum to see that it did not. Looking at the help for fivenum led me to boxplot.stats where I was that it w as not necessarily doing the same thing. HTH -- Ken Knoblauch Inserm U846 Institut Cellule Souche et Cerveau Département Neurosciences Intégratives 18 avenue du Doyen Lépine 69500 Bron France ______________________________________________ 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.
