Cooper, D. R., & Schindler, P. S. (2006). Business research methods (9th ed.). McGraw-Hill.

Cooper, Donald R., and Pamela S. Schindler. Business Research Methods. 9th ed. New Delhi: McGraw-Hill, 2006.

Cooper, Donald R., and Pamela S. Schindler. Business Research Methods. 9th ed. McGraw-Hill, 2006.