The association between, and stability of, clinical diagnosis and diagnosis derived
from the Autism Diagnostic Interview-Revised (ADI-R; Lord, Rutter, & Le Couteur, 1994) was
examined in a sample of prospectively identified children with childhood autism and other
pervasive developmental disorders assessed at the age of 20 months and 42 months. Clinical
diagnosis of autism was stable, with all children diagnosed with childhood autism at age 20
months receiving a diagnosis of childhood autism or a related pervasive developmental
disorder (PDD) at age 42 months. Clinical diagnosis of childhood autism was also
reasonably sensitive, with all children who went on to receive a clinical diagnosis of
childhood autism at 42 months being identified as having autism or PDD at 20 months.
However, clinical diagnosis for PDD and Asperger's syndrome lacked sensitivity at 20
months, with several children who subsequently received these diagnoses at 42 months
receiving diagnoses of language disorder or general developmental delay, as well as in two
cases being considered clinically normal, at the earlier timepoint. The ADI-R was found to
have good specificity but poor sensitivity at detecting childhood autism at 20 months;
however, the stability of diagnosis from 20 to 42 months was good. In addition, the ADI-R
at age 20 months was not sensitive to the detection of related PDDs or Asperger's syndrome.
The continuity and discontinuity between behavioural abnormalities identified at both
timepoints in the three domains of impairment in autism was examined, both in children who
met final clinical criteria for an autistic spectrum disorder, and for children with language
disorder who did not, as well as for a small sample of typically developing children.