Okun, Barbara F., author
Cengage Learning, 2015
Buku Teks
edited by Ray Woolfe, Windy Dryden, Sheelagh Strawbridge
Sage Publications, 2003
Buku Referensi
Arbuckle, Dugald S., author
Allyn and Bacon, 1961
Buku Teks
The British Psychological Society, 2018
Majalah, Jurnal, Buletin
The British Psychological Society, 2018
Majalah, Jurnal, Buletin