ORIGINAL ARTICLE Autism From 2 to 9 Years of Age

Context: Autism represents an unusual pattern of de-velopment beginning in the infant and toddler years. Objectives: To examine the stability of autism spec-trum diagnoses made at ages 2 through 9 years and iden-tify features that predicted later diagnosis. Design: Prospective study of diagnostic classifications from standardized instruments including a parent inter-view (Autism Diagnostic Interview–Revised [ADI-R]), an observational scale (Pre-Linguistic Autism Diagnostic Ob-servation Schedule/Autism Diagnostic Observation Sched-ule [ADOS]), and independent clinical diagnoses made at ages 2 and 9 years compared with a clinical research team’s criterion standard diagnoses. Setting: Three inception cohorts: consecutive referrals for autism assessment to (1) state-funded community au-tism centers, (2) a private university autism clinic, and (3) case controls with developmental delay from com-munity clinics. Participants: At 2 years of age, 192 autism referrals and 22 developmentally delayed case controls; 172 children seen at 9 years of age