Classification rules for basic phonological processing disabilities and nonverbal learning disabilities: formulation and external validity.
Rules for the classification of two subtypes of learning disabilities (LD), namely, Basic Phonological Processing Disabilities (BPPD) and Nonverbal Learning Disabilities (NLD), are reported. These rules (refined as a result of application to two separate samples of children with LD) were used to select children from an entirely new sample who could be classified as having "definite" or "probable" BPPD or NLD. As a first step in the external validation of these rules, the patterns of psychosocial functioning exhibited by these two subtypes of LD were determined. As predicted, the vast majority of the BPPD subtype exhibited a pattern most consistent with normal or relatively normal psychosocial adjustment, and no appreciable increase in the incidence of significant psychosocial disturbance with advancing years. Also, as predicted, an increasing incidence of internalized psychosocial dysfunction (a form of significant psychosocial disturbance) was evident in the NLD subtype with advancing years. It is clear that children classified as having BPPD or NLD using these rules exhibit quite different, and predicted, relative patterns of psychosocial functioning. Thus, in this sense, the rules have concurrent validity. Finally, sets of rules/criteria for classification are presented that reflect their actual incidence in the two subtypes of LD generated for use in the validation phase of this investigation. These rules would appear to be useful for clinical purposes. It is also clear that they should be subjected to further validation studies in a broader age range for clinical and research purposes.