[R] Question about histogram

Greg Snow Greg.Snow at imail.org
Thu Jan 13 21:22:01 CET 2011

Densities allow you to then plot a reference distribution, or the result of a call to density, or other density based lines on top of your histogram and everything is appropriately scaled and is fairly easy.

Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Longe
> Sent: Thursday, January 13, 2011 11:37 AM
> To: r-help at r-project.org
> Subject: [R] Question about histogram
> Dear list,
> I'm new to R, please bear with my silly questions.  I'm trying to get
> an
> understanding of why the results I get from a call to hist() are not as
> I thought I would get.  When I use the parameter freq=FALSE, I think
> the
> plot will contain bars that none of them is larger than 1, because
> they're probabilities.  But for my code, the bars exceeded 1.
> The actual data seems immaterial.  I tried with dummy data:
>  > hist(runif(1000), freq=FALSE)
> and the histogram includes bars well over 1 in height.  The man page
> says that freq=FALSE produces densities, so that the total area is 1.
> Clearly if all the values are between 0 and 1, as is the case here,
> some
> of the bars stand out above 1, for the area to be 1.  I thought that it
> is the sum of the bar heights that would be 1, so that the bars reflect
> probabilities for each interval, rather than densities.  So, the answer
> to my question would be "because it's densities, not probabilities",
> but
> then the question is, why densities and not probabilities?
> Regards,
> L.
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