On Mon, 2009-03-02 at 13:27 +0100, Johannes Elias wrote: > Dear R-Gurus, > > I wonder why 'density' values as shown in hist or plot(density(x)) are > sometimes over 1. How can that be? > > Example > > >hist(rnorm(1000,sd=.5),freq=FALSE) > > The resulting plot shows density values below 1 on the y-axis. However, > > >hist(rnorm(1000,sd=.1),freq=FALSE) > > shows density values over 1. > > How to interpret density values over 1? > > Greetings, > > Johannes
Johannes, Well density is not like probability In histogram with density the area is equal de probability in you example set.seed(123) hist(rnorm(1000,sd=.1),freq=FALSE) The interval of -0.05 and 0 have density=4 but a probability of number in this interval is 4*.05=.2 the fact set.seed(123) hist(rnorm(1000,sd=.1),freq=FALSE)$density [1] 0.09999998 0.28000000 0.94000000 1.98000000 2.60000000 4.00000000 [7] 4.04000000 2.92000000 1.66000000 0.92000000 0.44000000 0.10000000 [13] 0.02000000 set.seed(123) sum(hist(rnorm(1000,sd=.1),freq=FALSE)$density) [1] 1 So the sum of probability is 1 but the sum of density 20 -- Bernardo Rangel Tura, M.D,MPH,Ph.D National Institute of Cardiology Brazil ______________________________________________ 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.
