radon_chr.stan

data {
  int<lower=0> J;
  int<lower=0> N;
  array[N] int<lower=1, upper=J> county;
  vector[N] y;
}
parameters {
  vector[J] et;
  real mu_eta;
  real<lower=0, upper=100> sigma_eta;
  real<lower=0, upper=100> sigma_y;
}
transformed parameters {
  vector[J] eta;
  vector[N] y_hat;
  
  eta = 0.1 * mu_eta + sigma_eta * et;
  
  for (i in 1 : N) {
    y_hat[i] = eta[county[i]];
  }
}
model {
  et ~ normal(0, 1);
  mu_eta ~ normal(0, 1);
  y ~ normal(y_hat, sigma_y);
}