Dimensional approach to infantile autism in mentally retarded adults.

By use of latent trait models, a 7-item autism rating scale was established, based on the Medical Research Council's Schedule of Handicaps, Behaviours and Skills. Data from a community-based sample of 302 mentally retarded adults were assigning good internal validity to the autism scale, and revealing a distribution of symptoms consistent with dimensional, rather than categorical, distribution of infantile autism. A total of 23 (7.6%) of the sample were earlier diagnosed as suffering from infantile autism. Using this clinical diagnosis as a reference, the autism rating scale, with a cut-off point at greater than or equal to 2, established diagnoses with a sensitivity of 0.83 and specificity of 0.89.