Objectives: To examine the occurrence rate of these early signs over the first years of life in children with typical development (TD), in children with developmental delay (DD) and in children with ASD by comparing their developmental trajectories in amount of early signs of ASD.
Methods: Child care workers in day-care centres filled out the CESDD (Dereu et al., in preparation) for all children in their facility (N= 7007, age range 2 – 39 months). Children suspected of developmental problems, were assessed with the MSEL and ADOS and if necessary referred for clinical diagnosis and treatment. There were 43 children with ASD (M = 24 months, range 7 – 38) and 61 children with DD (M = 19 months, range 3 – 38).
Results: First, the occurrence of signs of ASD over time in typically developing children (n = 6909, M = 16 months, range 2 – 39) was analyzed. The total amount of early signs of ASD is very low but slightly increases over time (R² = .009, F(1, 6901) = 64.918, p < .0001; Total signs = 0.083 + 0.014*Age).
Secondary, the developmental trajectories of the amount of ASD symptoms was compared across diagnostic groups (TD, DD and ASD) using ANCOVA. Age was defined as ‘months from youngest ASD age’ (myda; see Thomas et al., 2009). The amount of early signs of ASD significantly differed at the youngest age across groups (F(2,7001) = 52.775, p < .001). Also, for the total sample the amount of signs increased over time (F(1,7001) = 165.125, p < .001). We also found a Group x Age interaction (F(2, 7001) = 74.863, p < .001) indicating that the increase in amount of signs of ASD significantly differed across diagnostic groups. The intercepts and slopes of the regression equations showed that at the youngest age children with DD had the most signs of ASD, but the increase in signs of ASD was about four times higher in the ASD group compared with the DD group.
Conclusions: Screening for ASD in young children should be done cautiously. The younger the children, the more likely it seems, based on the developmental trajectories found in this study, that cases of ASD will be missed and the more false positives will be generated by children with DD.