[R] Question about histogram

[Greg Snow]

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
801.408.8111


> -----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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