Sutton, Kelso
McGraw-Hill, 1949
Buku Teks
The Lancet, 1928"
Buku Teks
Atkinson, Lucky Jo
Mosby , 1995
Buku Teks
prepared by the Committee on Marketing Research Techniques of the American Marketing Society ; Ferdinand C. Wheeler, chairman
McGraw-Hill, 1937
Buku Teks
Nesbitt, Alexander
Dover Publications , 1957
Buku Teks