You expected the sum to be 1 and it is: > a <- hist(Y1, breaks=seq(0, 350, by=35), col="grey80", freq=FALSE) > a$density*35 [1] 0.27923387 0.14717742 0.09979839 0.08064516 0.06955645 0.06350806 [7] 0.05241935 0.05342742 0.05544355 0.09879032 > sum(a$density*35) [1] 1
Note that the first density multiplied by 35 is .279 exactly what you expected and the sum of the densities multiplied by the width of each bar (35) is 1. The height of the bar is not the probability, the area of the bar is the probability. ---------------------------------------------- David L Carlson Associate Professor of Anthropology Texas A&M University College Station, TX 77843-4352 > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] On Behalf Of Rolf Turner > Sent: Monday, March 12, 2012 3:53 AM > To: jpm miao > Cc: r-help@r-project.org > Subject: Re: [R] A question on histogram - area much less than 1 > > On 12/03/12 21:44, jpm miao wrote: > > Hello, > > > > Thanks very much for your kind response. Yes, if I multiply by the > > width "35", the area should be equal to one. > > > > How can I plot the probability bars rather than density bars? That > > is, I would like the height of the first bar to be 0.279, which is > the > > probability that the variable falls between 0 and 35. > > If you want probabilities rather than densities you should be using > barplot() rather > than histogram: > > TBL <- table(Y1) > barplot(TBL/sum(TBL)) > > cheers, > > Rolf Turner > > ______________________________________________ > 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. ______________________________________________ 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.
