[R] hist() basic question
Thomas Lumley
tlumley at u.washington.edu
Sat Mar 8 19:31:45 CET 2003
On Sat, 8 Mar 2003, juli g. pausas wrote:
> Hi,
> This is a very basic question, but I would like to undestand hist(). I
> thought that the hist( , freq=FALSE) should provide the relative
> frequencies (probabilities), and so they should sum 1, however:
No, it provides probability *densities*, which *integrate* to 1.
That is, the height of the bar is the relative frequency divided by the
width of the interval. This is important because
- it means histograms with different cutpoints are comparable
- it means histograms are comparable with mathematical densities such as
a Normal, and with kernel density estimates
- it means that the bars don't have to have the same width.
If histograms plotted relative frequencies there would be no need to
distinguish them from barplots.
-thomas
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