References
- Holland , P. W. 1986 . Statistics and causal inference . Journal of the American Statistics Association , 81 : 945 – 70 .
- Schneider , B. , Carnoy , M. , Kilpatrick , J. , Schmidt , W. H. and Shavelson , R. J. 2007 . Estimating Causal Effects Using Experimental and Observational Designs , Washington DC : American Educational Research Association .