References

Kish, Leslie. 1987. Statistical Design for Research. New York: John Wiley and Sons.

Singleton, Royce A., Jr. and Bruce C. Straits. 1999. Approaches to Social Research (3rd Edition). New York: Oxford University Press.

Wooldridge, Jeffrey M. 2003. Introductory Econometrics: A Modern Approach. Mason, Ohio: South-Western Publishers.