R help - Oct 2002 - how to overlay the histogram with fitted gamma density plot (emergent!!)

For a real data column X value ranged between (56.4521,32317.9) with missing
values, I need to overlay 2 plots: histogram & fitted gamma density.

I use following to generate histogram.

xbk_seq(50,33000,by=100)

hist(x,breaks=xbk)

But I don't know how to get "fitted gamma density"?

In SAS proc capability, I got Shape=2.59, Scale=3481).

But when I do

plot(dgamma(x, shape=2.59, rate=1,scale=3481)), it gives me a flat densed line
close to 0, which does not look correct.

Would anybody help me on this?

Thanks!

Shelton



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xiaodong jin <jin_xiaodong at yahoo.com> writes:
> For a real data column X value ranged between (56.4521,32317.9) with
missing values, I need to overlay 2 plots: histogram & fitted gamma density.
> 
> I use following to generate histogram.
> 
> xbk_seq(50,33000,by=100)
> 
> hist(x,breaks=xbk)
> 
> But I don't know how to get "fitted gamma density"?
> 
> In SAS proc capability, I got Shape=2.59, Scale=3481).
> 
> But when I do
> 
> plot(dgamma(x, shape=2.59, rate=1,scale=3481)), it gives me a flat densed
line close to 0, which does not look correct.
> 
> Would anybody help me on this?
First of all, you need to make sure that your histogram is on "density
scale" (i.e. not raw bin counts) by using prob=TRUE. Then comes the
issue of checking that SAS and R agree on the parametrization of the
gamma distribution. 

The MASS library has fitdistr() which might be helpful.

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