TULL DONALD S. (1987). MARKETING RESEARCH: MEASUREMENT AND METHOD (4.). MACMILLAN.
Lua i Stíl Chicago (17ú heag.)TULL DONALD S. MARKETING RESEARCH: MEASUREMENT AND METHOD. 4. NEW YARK: MACMILLAN, 1987.
Lua MLA (9ú heag.)TULL DONALD S. MARKETING RESEARCH: MEASUREMENT AND METHOD. 4. MACMILLAN, 1987.
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