The name is absent

Autism prodrome 14 of 89

tea-set, doll play, object substitution) and joint attention behaviors, pointing for
interest (in combination with eye contact) and following gaze, by parental report and
health practitioner observation through direct testing.

The first study tested the effectiveness of the CHAT as a screening instrument
in a genetic high-risk sample of forty-one 18-month-old younger siblings of children
diagnosed with autism or with ASD (Baron-Cohen, 1992; see Table 2). An often
overlooked point is that this study was, in essence, the first ‘high risk sibling’ study of
ASDs. Whilst none of 50 comparison 18 month olds failed all 5 key items, four of the
children in the high-risk sibling group did so. A year later, when the children were 30
months old, a follow-up was carried out. None of the comparison children had been
diagnosed with ASD. The four children in the high-risk group who had failed the five
key items were diagnosed with autism.

To test whether the CHAT could prospectively identify ASD cases from a
large general population, community practitioners in the South Thames region of the
UK used the questionnaire with 16,235 18-month-olds as part of routine health
surveillance (Baron-Cohen et al., 1996; Baird et al., 2000). On the basis of the high
risk pilot it was predicted that those children who at 18 months failed all five key
items would be at the greatest risk for ASD and children who failed both items
measuring protodeclarative pointing (pointing for interest) would be at next greatest
risk. In order to minimize false positives, a two-stage screening procedure was
adopted so that screen positive children received a second administration of the screen
one-month later, via a telephone follow-up. Used in this 2-stage way, the positive
predictive value of the screening instrument was high (83% for ASD using the high-
risk threshold). This study found that failing a combination of joint attention and
pretend play items (by both parental report and health practitioner observation, and on

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