Stability of the ADI-R
14
such as repetition effects and differences in administration/scoring of the ADI-R by different examiners
over the 4 time points. The present sample was older when first seen (3.5 vs. 2.5 years in the Charman
study) with some participants as old as 4 years at T1, thus greater stability might be expected.
However, an examination of ADI-R trajectories in children from 3 to 7 years in the Charman et al.
study still indicated considerably more change, with 11 out of that sample of 26, changing from ADI-R
autism-positive ratings at age 3 to “non-autistic” ratings at age 7. One child moved from “non-autistic”
to “autistic” over the same period. Although differences in the age range between the Charman et al.
study and the current sample may account for some of the differences in overall stability, the reasons
for this apparent discrepancy are not entirely clear and indeed, given the wide spread of intellectual and
verbal ability in the present sample (initial IQ 16-130+; only 9 verbal participants at T1) one might
have expected considerably less stability than was actually recorded. The methodological factors
outlined in the Charman et al. study are unlikely to have played a role in the current study given the
longer time period between assessments, the small number of interviewers involved and the fact that
inter-rater reliability for ADI-R scoring was very high at FU.
At the domain level, however, the findings generally parallel those of Charman et al. (2005) and a
number of other studies (Boelte & Poutska 2000; Fecteau et al., 2003; Piven et al., 1996; Seltzer et al,
2003; Shattuck et al., 2007; Starr et al., 2003) indicating improvements in symptom severity over time,
especially on scores in the RSI and NVC domains of the ADI-R. Total ADI-R scores also decreased
significantly. These results indicate that such improvements in the severity of autism-specific
behaviours can occur in children who fall within the moderate-severe range of intellectual impairment
as well as those of higher verbal and cognitive ability.