Update ch9 models

Author: Andrew Johnson

ARM/Ch.9/electric_inter.stan

@@ -5,14 +5,15 @@ data {
   vector[N] pre_test;
 }
 transformed data {
-  vector[N] inter;           // interaction
-  inter = treatment .* pre_test;
+  // interaction
+  vector[N] inter = treatment .* pre_test;
+  matrix[N,3] x = [treatment', pre_test', inter']';
 }
 parameters {
-  vector[4] beta;
+  real alpha;
+  vector[3] beta;
   real<lower=0> sigma;
 }
 model {
-  post_test ~ normal(beta[1] + beta[2] * treatment + beta[3] * pre_test
-                     + beta[4] * inter, sigma);
+  post_test ~ normal_id_glm(x, alpha, beta, sigma);
 }

ARM/Ch.9/electric_supp.stan

@@ -4,10 +4,14 @@ data {
   vector[N] supp;
   vector[N] pre_test;
 }
+transformed data {
+  matrix[N,2] x = [supp', pre_test']';
+}
 parameters {
-  vector[3] beta;
+  real alpha;
+  vector[2] beta;
   real<lower=0> sigma;
 }
 model {
-  post_test ~ normal(beta[1] + beta[2] * supp + beta[3] * pre_test, sigma);
+  post_test ~ normal_id_glm(x, alpha, beta, sigma);
 }

ARM/Ch.9/electric_tr.stan

@@ -3,10 +3,14 @@ data {
   vector[N] post_test;
   vector[N] treatment;
 }
+transformed data {
+  matrix[N,1] x = [treatment']';
+}
 parameters {
+  real alpha;
   vector[2] beta;
   real<lower=0> sigma;
 }
 model {
-  post_test ~ normal(beta[1] + beta[2] * treatment, sigma);
+  post_test ~ normal_id_glm(x, alpha, beta, sigma);
 }

ARM/Ch.9/electric_trpre.stan

@@ -4,10 +4,14 @@ data {
   vector[N] treatment;
   vector[N] pre_test;
 }
+transformed data {
+  matrix[N,2] x = [treatment', pre_test']';
+}
 parameters {
-  vector[3] beta;
+  real alpha;
+  vector[2] beta;
   real<lower=0> sigma;
 }
 model {
-  post_test ~ normal(beta[1] + beta[2] * treatment + beta[3] * pre_test, sigma);
+  post_test ~ normal_id_glm(x, alpha, beta, sigma);
 }