Data
====

1. electric_gradeX.data.R, where X = 1, 2, 3, 4
Data from an educational experiment performed around 1970 on a set of
elementary school classes.
The treatment was exposure to a new educational television show called The
Electric Company.
  - N        : number of observations
  - grade    : one of four grades
  - pre_test : reading test score at the beginning of the school year
  - post_test: reading test score at the end of the school year
  - treatment: 1 if the class was exposed to the television show

2. electric_gradeX_supp.data.R, where X = 1, 2, 3, 4
  - N        : number of observations
  - grade    : one of four grades
  - post_test: reading test score at the end of the school year
  - pre_test : reading test score at the beginning of the school year
  - treatment: 1 (only classes exposed to the television show)
  - supp     : 1 if the teacher chose to supplement the regular reading program
             0 if the teacher chose to replace the regular reading program

Models
======

1. One predictor
  electric_tr.stan: lm(post_test ~ treatment)

2. Multiple predictors without interaction
  electric_trpre.stan: lm(post_test ~ treatment + pre_test)
  electric_supp.stan : lm(post_test ~ supp + pre_test)

3. Multiple predictors with interaction
  electric_inter.stan: lm(post_test ~ treatment + pre_test + treatment:pre_test)