/* Multilevel Analysis

MIXED
  score  WITH time
  /FIXED = time
  /METHOD = REML
  /PRINT SOLUTION COVB
  /RANDOM = INTERCEPT time  | SUBJECT(school) COVTYPE(ID)
  /RANDOM = INTERCEPT time  | SUBJECT(school*class) COVTYPE(ID) 
  /RANDOM = INTERCEPT time  | SUBJECT(school*class*student) COVTYPE(ID) .