1. American Psychiatric Association. Diagnostic and statistical manual of mental disorders. 4th ed. Washington, DC: American Psychiatric Association, 1994: 39–46
2. American Association on Mental Retardation. Mental retardation: definition, classification, and systems of supports. 9th ed. Washington, DC: American Association on Mental Retardation, 1992: 5–9
3. Accardo PJ, Capute AJ. Mental retardation. In: Oski FA, DeAngelis CD, Feigin RD, et al, eds. Principles and practices of pediatrics. 2d ed. Philadelphia: Lippincott, 1994:673–8