Michal-Smith, H. (1956). Classification of mental retardation. In H. Michal-Smith, The mentally retarded patient (pp. 27-42). Philadelphia, PA, US: J B Lippincott Company.
http://dx.doi.org/10.1037/14749-003
There are many difficulties in classifying mental retardation because of the limitations of our present knowledge as to the exact etiologic factors and pathologic processes involved. Therefore, a completely satisfactory classification of all forms of mental retardation has not yet been devised. At the Clinic for Mentally Retarded Children at Flower and Fifth Avenue Hospitals, we use the following classifications which consider, as completely as possible, both the pathologic and the etiologic aspects of each individual instance of retardation. (PsycINFO Database Record (c) 2016 APA, all rights reserved)