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

[Rolf Turner]

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