Hierarchical logistic regression

[Anonymous]

Hi,

I am currently learning to use JAGS with rjags. I am starting by trying to
replicate some of the WinBUGS code and results from Royle and Dorazio's
Hierarchical Modeling and Inference in Ecology. The current model I am trying
to fit is a fairly simple hierarchical logistic regression. I am getting
stumped by an error message:

Error in node y

Observed node inconsistent with unobserved parents at initialization

At other times the error has occured in y or y, but these three nodes are the
first 3 non-zero nodes in the y variable. The model specification I am using
is:

model{
        for(i in 1:M){
            z[i]~ dbern(psi[i])
            psi[i] <- ilogit( b0+b1*elev[i]+b2*elev2[i]+b3*forest[i])
            y[i]~dbin(z[i]*p,J[i])
            }
        p~dunif(0,1)
        b0~dnorm(0,.001)
        b1~dnorm(0,.001)
        b2~dnorm(0,.001)
        b3~dnorm(0,.001)

    }

I have posted my r code and the data here:
https://public.me.com/pokey54

Any help in interpreting or troubleshooting this error is appreciated.

Thanks!

[Martyn Plummer]

In your code you are randomly initializing the latent variable z to be 0 or 1.
But if z = 0 then y = 0. The problem arises because you've got some non-zero y
values with zero z.

To fix the code, modify your initial values for z from this

z=rbinom(M,1,.4)

to this

z=ifelse(y>0, 1, rbinom(M, 1, 0.4))