[R] 'stretching' a binomial variable

[Robert A LaBudde]

At 06:49 AM 3/27/2009, imicola wrote:

>Hi,
>
>Im carrying out some Bayesian analysis using a binomial response variable
>(proportion: 0 to 1), but most of my observations have a value of 0 and many
>have very small values (i.e. 0.001).  I'm having troubles getting my MCMC
>algorithm to converge, so I have decided to try normalising my response
>variable to see if this helps.
>
>I want it to stay between 0 and 1 but to have a larger range of values, or
>just for them all to be slightly higher.
>
>Does anyone know the best way to acheive this?  I could just add a value to
>each observation (say 10 to increase the proportion a bit, but ensuring it
>would still be between 0 and 1) - would that be ok?  Or is there a better
>way to stretch the values up?
>
>Sorry - i know its not really an R specific question, but I have never found
>a forum with as many stats litterate people as this one :-)
>
>Cheers - any advice much appreciated!
>
>nicola

Work with events instead of proportions, and use a Poisson model.

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Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral at lcfltd.com
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