Hi Sebatiano, Take a look at
> require(MCMCpack) > ?MCpoissongamma HTH, Jorge On Wed, Sep 21, 2011 at 5:25 AM, Sebastiano Putoto <> wrote: > Good afternoon/morning readers. This is the first time I am trying to run > some Bayesian computation in R, and am experiencing a few problems. > > I am working on a Poisson model for cancer rates which has a conjugate > Gamma > prior. > > 1) The first question is precisely how I work out the parameters. > > #Suppose I assign values to theta with seq() > theta<-seq(0,1,len=500) > > #Then I try out the parameters that seem to fit with a certain prior idea > on > theta (see next) > a=182 > b=3530 > gaprior<-dgamma(theta,a,b) > > It should work by trial-and-error (according to "Bayesian Computation with > R") , but how can I check the parameters turned out well: should I just > look > at the plot, or evaluate it through the 1 - pgamma(x,a,b) function, having > knowledge of the 5th percentile (data from US Cancer Statistics)? > > 2) Then, the next problem I have regards the likelihood distribution. > > #Having the react table, I name the columns (with y=deaths, and > x=exposures) > react > x y > 1 6 15 > 2 5 16 > 3 3 12 > 4 4 6 > 5 27 77 > 6 7 17 > 7 4 11 > 8 5 10 > 9 23 63 > 10 11 29 > > yr <- react[,2] > xr <- react[,1] > > > > #I then compute the likelihood > poislike=dpois(yr, theta*xr) > > #And this is what I come up with, which I really don't understand. > poislike > [1] 0 0 0 0 0 0 0 0 0 0 > > The values shouldn't be all null, otherwise my posterior cannot be computed > properly. Does anyone have any idea on where I could possibly have messed > it > up? > > Thank you very much for your attention. > > Regards, > > Sebastiano Putoto (University of Pavia, Italy) > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
