[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.


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