Knapp, Brian J.
Longman, 1992
Buku Teks
Ashby, Eric
Stanford University Press, 1978
Buku Teks
Information Dynamic, Inc. , 1981
Buku Teks
proposed by Centre for Research of Human Resources and the Environment
University of Indonesia, 1990
Buku Teks
Meyer, Evelyn E.
World Health Organization, 1975
Buku Teks