libname data "C:\Documents and Settings\ejohnson\My Documents\MultilevelModels";

proc contents data=data.cognitive;
run;

data data;
set data.cognitive;
calorie = (trt=1);
meat = (trt=2);
milk = (trt=3);
run;

** OLS regression **;
proc glm data=data;
model ravens = calorie meat milk / solution;
run;quit;

** 3-level random intercept model **;
** these proc mixed take a bit to run;
proc mixed data=data;
class schoolid id;
model ravens = calorie meat milk / solution;
random intercept schoolid / subject=id;
run;

** Add the other variables to the model for ravens score;
proc mixed data=data;
class schoolid id;
model ravens = calorie meat milk age_at_time0 gender ses1 head_circ readtest writetest / solution;
random intercept schoolid / subject=id;
run;

** Linear time effect;
** Variable rn is the time in weeks;
proc mixed data=data;
class id;
model ravens = rn calorie meat milk age_at_time0 gender ses1 head_circ readtest writetest / solution;
random intercept / subject=id;
run;
 
** random intercept and slope;
proc mixed data=data;
class id;
model ravens = rn calorie meat milk age_at_time0 gender ses1 head_circ readtest writetest / solution;
random intercept rn / subject=id type=un;
* Note, these variance and covariance of the random effects are listed in the output;
* according to the order listed in the random statement!;
run;