1. Alonso, W.Choosing and Building Models for Prediction. Presented to the Highway Research Board Conference on Urban Models. New Hampshire: Dartmouth College.
2. The Use of Transformations
3. Blalock, H.M. 1961b.Causal Inferences in Nonexperimental Research, 10–10. University of North Carolina Press.
4. Ferber, R. and Verdoorn, O.J. 1962.Research Methods in Business and Economics, 64–64. New York: Macmillan.