Recent evidence suggests that the structure of autistic traits varies along more than one single underlying continuum.
To evaluate the dimensional structure of a revised version of the Checklist for Autism in Toddlers (the Quantitative - Checklist for Autism in Toddlers [Q-CHAT]) in the general population.
The Q-CHAT was sent to parents of 18 – 24 months olds from two general populations in the Eastern Region, UK. Exploratory Factor Analysis (EFA) (using MPlus) was run on the first sample (N=754) to obtain the factor structures with up to six factors using the robust Weighted Least Squares Mean and Variance (WLSMV) estimator. Poorly and negatively loading items were dropped until all remaining items loaded ≥0.35 on each factor. EFA was re-run on the second sample (N=819), followed by Confirmatory Factor Analysis (CFA) on the remaining 17 items to confirm the factor structure.
The EFA revealed two possible factor structures. The two factor solution separated social from non-social items (RMSEA=0.095). The three factor solution reflected the domains of social interaction, communication and repetitive and stereotyped behaviours (RMSEA=0.051). The CFA confirmed that the three factor solution (CFI=0.92, TLI=0.93, RMSEA=0.055, WRMR=1.338) marginally fit the data better than the two (CFI=0.838, TLI=0.855, RMSEA=0.077, WRMR=1.759) factor structure. The social and non-social factors in the two factor solution were only weakly correlated (r=0.14, p=0.001), indicating that these domains are largely independent. In the three factor solution, the social interaction factor was not correlated with the repetitive and stereotyped behaviour factor.
No evidence was found to support a single continuum of autistic traits; rather the data support at least a bi-dimensional approach underlying autistic traits in toddlers. Ongoing work is testing the sensitivity and specificity of the Q-CHAT in a total population.