Subjects were recruited from 2 sources: general community referral (eg, Web site) and a general population-based screening method called the 1-Year Well-Baby Check-Up Approach (K.P., C. Carter, PhD, M. Weinfeld, PhD, J.D., R.H., R. Bjork, MD, N. Gallagher, BA, unpublished data, 2006-2009). Using this method, toddlers at risk for an ASD, language delay, and DD as young as 12 months were identified with a broadband screening instrument, the Communication and Symbolic Behavior Scales Developmental Profile Infant-Toddler Checklist,41,42 and were recruited and tracked every 6 months until their third birthday. This method thus allowed for the prospective study of autism beginning at 12 months of age. Typically developing controls were obtained from community referrals. All toddlers participated in a series of tests across multiple 2-hour sessions that included the Autism Diagnostic Observation Schedule–Toddler Module (ADOS-T), newly validated for use with infants as young as 12 months,43 and the Mullen Scales of Early Learning.44 Parents were also interviewed with the Vineland Adaptive Behavior Scales.45 Toddlers participated in additional behavioral (eg, play) and biological (eg, magnetic resonance imaging) tests as part of a larger study. (For more information, see www.autismsandiego.org.) All standardized assessments were administered by 2 highly experienced
PhD-level psychologists with more than 10 years' combined experience in autism.