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

[Benjamin Caldwell]

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?

Thanks

*Ben Caldwell*

PhD Candidate
University of California, Berkeley