* random intercept model .
MIXED
  hamd  WITH week
  /FIXED = week  
  /METHOD = ML
  /PRINT = SOLUTION TESTCOV
 /RANDOM INTERCEPT | SUBJECT(id)  .

* random trend model .
MIXED
  hamd  WITH week
  /FIXED = week  
  /METHOD = ML
  /PRINT = SOLUTION TESTCOV
 /RANDOM INTERCEPT week  | SUBJECT(id) COVTYPE(UN) .

* random trend model with group effects .
MIXED
  hamd  WITH week endog endweek
  /FIXED = week  endog endweek
  /METHOD = ML
  /PRINT = SOLUTION TESTCOV
 /RANDOM INTERCEPT week  | SUBJECT(id) COVTYPE(UN) .

* compute time squared .
COMPUTE week2 = week*week .
EXECUTE . 

* random quadratic trend model .
MIXED
  hamd  WITH week week2
  /FIXED = week  week2 
  /METHOD = ML
  /PRINT = SOLUTION TESTCOV
 /RANDOM INTERCEPT week week2  | SUBJECT(id) COVTYPE(UN) .

* getting predicted values from random trend model .
MIXED
  hamd  WITH week
  /FIXED = week  
  /METHOD = ML
  /PRINT = SOLUTION TESTCOV
 /RANDOM INTERCEPT week  | SUBJECT(id) COVTYPE(UN)
  /SAVE = PRED .

* plotting predicted values across time . 
EXE.
IGRAPH /VIEWNAME='Scatterplot' /X1 = VAR(week) TYPE = CATEGORICAL /Y = VAR
 (PRED_1) TYPE = SCALE /PANEL =  VAR(id) /SCATTER COINCIDENT = NONE.