[R] hist() and density
Bill Simpson
wsi at gcal.ac.uk
Fri Nov 17 10:47:20 CET 2000
There were some questions about hist() a couple of days ago which
triggered this post. My question/suggestion is about the y-axis in hist.
There are reasons to prefer making the y-axis density=relative
frequency/bin width. One reason is that the height of the plot does not
depend on the bin width; another is that if your histogram is in density
then you can easily superimpose a smooth theoretical pdf on top--they will
be on the same scale. (BTW the best intro stats book--Freedman et al--only
shows students how to make density histograms)
It doesn't seem easy to make density on the y-axis with the current
hist(). The freq argument only lets you choose counts (TRUE) or relative
frequency (FALSE). I would like to suggest that freq (or some renamed
version of the argument) take on the values
counts
freqs
densities
So that you can easily do a density histogram.
The strange thing to me is that if you do
h<-hist(...)
you get h$intensities, which is the densities. So hist calculates the
densities, but doesn't let you plot them?
May I suggest you call it $densities? I don't know why you call it
intensities--I thought in stats intensity meant the instantaneous rate of
a point process. Also I find the help quite obscure:
intensities
values f^(x[i]), as estimated density values. If
all(diff(breaks) == 1), they are the relative frequencies counts/n and in
general satisfy sum[i; f^(x[i]) (b[i+1]-b[i])] = 1, where b[i] =
breaks[i].
May I suggest:
densities estimated densities calculated by relative frequency/bin
width, where relative frequency is count/n
(I can't figure out why you've got powering ^ in there!)
Bill Simpson
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