speech-maturity-tests/model.stan

data {
    int N;
    vector<lower=0>[N] age;
    vector<lower=0,upper=1>[N] ratio;
}

transformed data {
    int M = 500;
    real lambda = -log(M);
    vector<lower=0,upper=5>[M] c;

    for (i in 1:M) {
        c[i] = i*5.0/(1.0*M);
    }
}

parameters {
    real<lower=0,upper=1> mu_low;
    real<lower=0,upper=1> mu_up;
    real<lower=1> eta;
}

transformed parameters {
  vector[M] lp;
  lp = rep_vector(lambda, M);
  
  for (m in 1:M) {
    for (n in 1:N) {
      lp[m] = lp[m] + beta_proportion_lpdf(ratio[n] | age[n] < c[m] ? mu_low : mu_up, eta);
    }
  }
}

model {
    mu_low ~ uniform(0, 1);
    mu_up ~ uniform(0, 1);
    eta ~ pareto(1,1.5);
    
    target += log_sum_exp(lp);
}