Re: [R] graphs of gamma, normal fit to a histogram are about half as large as they should be

From: Benjamin Caldwell <btcaldwell_at_berkeley.edu>
Date: Sun, 15 May 2011 22:01:50 -0700

Hmm; still missing something - hist defaults to frequencies, not prob. densities; and, I thought I'd scaled the fitted lines to the values in the data frame. Just going with it, I specified freq=FALSE, and the prob density was of course at a different order of magnitude than the lines.

What are you trying to hint at?

On Fri, May 13, 2011 at 6:05 PM, Rolf Turner <rolf.turner_at_xtra.co.nz> wrote:

> On 14/05/11 10:00, Benjamin Caldwell wrote:
>
>> Hello,
>>
>> I'm trying to compare the fit of two distributions, normal and gamma, to a
>> histogram of my response variable.
>>
>>
>> rate<-mean(na.omit(rwb$post.f.crwn.length))/var(na.omit(rwb$post.f.crwn.length))
>> shape<-rate*mean(na.omit(rwb$post.f.crwn.length))
>> hist((rwb$post.f.crwn.length), main="rwb$post.f.crwn.length")
>>
>> lines(seq(0.01,70,0.01),length(rwb$post.f.crwn.length)*dgamma(seq(0.01,70,0.01),shape,rate))
>>
>> lines(seq(0,70,0.1),length(na.omit(rwb$post.f.crwn.length))*dnorm(seq(0,70,.1),mean(na.omit(rwb$post.f.crwn.length)),sqrt(var(na.omit(rwb$post.f.crwn.length))))
>>
>> However, the height of the two curves are about 1/3 to 1/4 the height that
>> they should be compared to the histogram. Any ideas?
>>
>
> Yes. Read the help on "hist"! (Hint: Pay particular attention to the
> "freq" and/or "probability" arguments.)
>
> cheers,
>
> Rolf Turner
>

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