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From the “main GUSTO cohort” (n = 1162), a subsample of participants were invited for more detailed follow-up neurocognitive phenotyping and neuropsychological assessments at regular intervals, the “GUSTO Neurodevelopmental Cohort”.
At 18 months, 431 toddlers and their caregivers participated in the scheduled neurocognitive follow-up; at 24 months, 514 caregiver-toddler pairs participated.
Finally, twin and other studies investigating autistic traits in the general population and in those with ASD have shown that the etiology of autistic traits is likely to be more similar than different to that of ASD (see  for a review).
Sensitivity, specificity, cutoff values, or the Q-CHAT’s factor structure were not examined.So far, the Quantitative-Checklist for Autism in Toddlers (Q-CHAT) is one of very few measures developed for use with toddlers as young as 18 months, but little is known about its measurement properties and factor structure.The present study examined internal consistency, factor structure, test-retest stability, and convergent validity of the Q-CHAT in a sample of toddlers in Singapore whose caregivers completed the Q-CHAT at 18 (n = 368) and 24 months (n = 396).Adopting a dimensional-quantitative approach, each Q-CHAT item is scored on a 5-point scale which allows respondents to report the relative frequency, typicality, or severity of observed autistic traits rather than their absolute presence or absence, as in the dichotomous yes/no ratings of the original Checklist for Autism in Toddlers (CHAT) , from which the Q-CHAT was developed.In the first study to employ and report on the Q-CHAT involving caregivers of 754 toddlers aged 18–24 months in the UK, the Q-CHAT total scores were normally distributed, had an internal consistency α value of .67, and excellent test-retest reliability after 1 month (r = .82) .