REFERENCES
- Littell , R. , Freund , R. and Spector , P. 1991 . SAS® System for Linear Models, , 3rd ed. Cary , NC : SAS Institute. .
- Littell , R. , Milliken , G. , Stroup , W. and Wolfinger , R. 1996 . SAS® System for Mixed Models Cary , NC : SAS Institute. .