We tested whether developmental coordination disorder (DCD) and mixed receptive expressive language disorder (RELD) are valid diagnoses by assessing whether they are separated from each other, from other childhood disorders, and from normality by natural boundaries termed zones of rarity. Standardized measures of intelligence, language, motor…

We assessed whether the stereotyped movements (SM) that are a defining characteristic of autism are discriminable from those observed in other disorders, and whether stereotyped self-injurious movements, which are excluded as exemplars of SM in DSM-IV, differ from other SM in severity or in kind. We used the Stereotyped and Self-Injurious Movement…