Tull, D. S., & Hawkins, D. I. (1987). Marketing research: Measurement and method : a text with cases (4th ed.). Macmillan Pub. Co. ; Collier Macmillan.

Tull, Donald S., and Del I. Hawkins. Marketing Research: Measurement and Method : A Text with Cases. 4th ed. New York : London: Macmillan Pub. Co. ; Collier Macmillan, 1987.

Tull, Donald S., and Del I. Hawkins. Marketing Research: Measurement and Method : A Text with Cases. 4th ed. Macmillan Pub. Co. ; Collier Macmillan, 1987.