Re: [R] Fitting a distribution to peaks in histogram

From: Ulrik Stervbo <ulriks_at_ruc.dk>
Date: Thu 20 Jul 2006 - 02:56:32 EST

On 7/19/06, hadley wickham <h.wickham@gmail.com> wrote:
> > I would like to fit a distribution to each of the peaks in a histogram, such
> > as this: http://photos1.blogger.com/blogger/7029/2724/1600/DU145-Bax3-Bcl-xL.png
>
> As a first shot, I'd try fitting a mixture of gamma distributions (say
> 3), plus a constant term for the highest bin. You could do this using
> ML. If the number of peaks is truly unknown, this will be a little
> trickier but still possible and you could use the LRT to chose between
> them.

Can you be a bit more excact? I a biologist and relatively new to R

>
> > Integrate the area between each two peaks, using the means and widths of the
> > distributions fitted to the two peaks. I will be using the integrate
> > function
>
> Why do you want to do this?

I am measureing the amount of DNA in cells, and I need to know the percentage of cells in a part of the cell cycle; that the percentage of cells in the first peak, in the second peak and so on. I want to integrate the area between to two cells, because that apparently is how its none (as far as I can tell from the literature)

>
> >
> > The histogram is based on approximately 15000 events, which makes Mclust and
> > pam (which both delivers the information I need) less useful.
>
> If you have unbinned data, it would be better (more precise/powerful)
> to use that.

It very probably is better, but mclust had no result after running for at least 2 hours (I terminated the function after two hours), and as I generate 50-100 datasets, such as the one used for the histogram, as week, I would like to find a faster solution
>
> Regards,
>
> Hadley
>

Thanks
Ulrik

-- 
Blog: http://ulrikstervbo.blogspot.com

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