1. Block S. Browning S. & McGrath G. Humor in group psychotherapy. Br J Med Psychol 1983; 56:89-97.
2. Darwin C. The expression of emotion in man and animal. Chicago: University of Chicago Press 1965.
3. DeWane C. Humor in therapy. Social Work 1978; 23(6):508-510.
4. Freud S. Jokes and their relation io the unconscious (8th ed.). London: Hogarth Press 1960. (Original work published 1923).
5. Greig J. The psychology of laughter and comedy. New York: Cooper Square Publishers Inc. 1969. (Original work published 1923 New York: Dodd-Mead).