1. Abraham, F. P., & Lloyd-Still, J. D. (1984). Chronic constipation in childhood: A longitudinal study of 186 patients. Journal of Pediatric Gastroenterology and Nutrition, 3, 460–467.
2. American Psychiatric Association (APA) (2000). Diagnostic and statistical manual of mental disorders(4th ed., Text Revision). Washington, DC: American Psychiatric Association.
3. Azrin, N. H. (1973). On toilet training the severelyand profoundly retarded. Journal of Research and Training, 1, 9–13.
4. Barr, R. G., Levine, M. D., Wilkinson, R. H., & Mulvihill, D. (1979). Chronic and occult stool retention: A clinical tool for its evaluation in school aged children. Clinical Pediatrics, 18, 674–686.
5. Bellman, M. (1966). Studies on encopresis. Acta Paediatrica Scandinavica, 170(Suppl.), 1–137.