model
{    
  for( year in 1 : N ) {
       D[year] ~ dpois(mu[year])    
       log(mu[year]) <- b[1] + step(year - changeyear) * b[2]    }
  for (j in 1:2) {b[j] ~ dnorm( 0.0,1.0E-6)}
  changeyear ~ dunif(1,N) 
}