R help - May 2011 - How to fit a random data into Beta distribution?

Hi,
I have some random data and i want to find out the parameters of Beta
distribution ( a and b) such that this data approximately fits into
this distribution. I have tried by plot the histograms and graph, but
it requires lot of tuning and i am unable to do that. can anyone tell
me how to do it programmitically in R?

Regards,
Som Shekhar

library(MASS)
fitdistr(x,"beta",list(shape1=1,shape2=1))



On Tue, May 3, 2011 at 9:44 PM, Shekhar <shekhar2581 at gmail.com>
wrote:
>
> Hi,
> I have some random data and i want to find out the parameters of Beta
> distribution ( a and b) such that this data approximately fits into
> this distribution. I have tried by plot the histograms and graph, but
> it requires lot of tuning and i am unable to do that. can anyone tell
> me how to do it programmitically in R?
>
> Regards,
> Som Shekhar
>
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On May 11, 2011, at 11:17 PM, MikeK wrote:
> I am also trying to fit data to a beta distribution.
>
> In Ang and Tang, Probability Concepts in Engineering, 2nd Ed., page  
> 127-9,
> they describe a variant of a beta distribution with additional  
> parameters
> than the standard beta distribution, enabling specification of a max  
> and min
> value other than 0,1. This would be very useful for my purposes.
>
> Any thoughts on how to fit a distribution directly to this variant  
> of the
> beta distribution, without starting from scratch?
>
Scale your data to [0,1], fit, predict, invert the scaling.

xscaled <- (x-min(x))/max(x)
....
xrescaled <- max(x)*xscaled + min(x)

(Better check that I made the correct order of those operations. The  
first attempt was wrong ... I think.)

-- 
David Winsemius, MD
West Hartford, CT