1. 1. Luckasson R, Borthwick-Duffy S, Buntinx WHE, Coulter DL, Craig EM, Reeve A, Schalock RL, Snell ME, Spitalnik DM, Spreat S, Tasse, MJ. Mental retardation: Definition, classification, and systems of supports (10th Ed.). Washington, DC: American Association on Mental Retardation, 2002.
2. 2. Heber R. A manual on terminology and classification in mental retardation. Am J Ment Defic. 1959 Sep; Suppl 64(2): 1-111.
3. 3. Heber R. Modifications in the manual on terminology and classification in mental retardation. Am J Ment Defic. 1961 Jan; 65: 499-500.
4. 4. World Health Organization. ICD-10 Classification of Mental and Behavioural Disorders: Diagnostic Criteria for Research. Geneva, Switzerland: World Health Organization, 1993.
5. 5. National Alliance on Mental Illness (NAMI). Early Psychosis and Psychosis. Taken from the webpage: https://www.nami.org/earlypsychosis on 02/06/2017.