Likert, Rensis
McGraw-Hill, 1961
Buku Teks
by James J. Nora [and others]
[publisher not identified], [date of publication not identified]
Buku Teks
James J. Nora [and others]
Lea & Febiger , 1993
Buku Teks
Barker, D.J.P., author
Churchil Livingstone, 1976
Buku Teks
edited by L.G. Whitby and Walter Lutz
Churchill Livingstone, 1971
Buku Referensi