'stretching' a binomial variable
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. ================================================================ Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: ral at lcfltd.com Least Cost Formulations, Ltd. URL: http://lcfltd.com/ 824 Timberlake Drive Tel: 757-467-0954 Virginia Beach, VA 23464-3239 Fax: 757-467-2947 "Vere scire est per causas scire"