BOYD HARPER W. (1990). MARKETING RESEARCH (7.). RICHARD D.IRWIN INC.
Lua i Stíl Chicago (17ú heag.)BOYD HARPER W. MARKETING RESEARCH. 7. ILLINOIS U.S.A: RICHARD D.IRWIN INC, 1990.
Lua MLA (9ú heag.)BOYD HARPER W. MARKETING RESEARCH. 7. RICHARD D.IRWIN INC, 1990.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.