Effectiveness of large-scale community-based Intensive Behavioral Intervention: A waitlist comparison study exploring outcomes and predictors

File review data were used to explore the impact of a large-scale publicly funded Intensive Behavioral Intervention (IBI) program for young children with autism. Outcomes were compared for 61 children who received IBI and 61 individually matched children from a waitlist comparison group. In addition, predictors of better cognitive outcomes were explored (n = 142). Although random assignment did not take place, a standardized waitlist management system was used that did not include any prioritization other than time of referral. Groups did not differ significantly on available measures at intake. The treatment period tended to be longer than the waitlist period and this difference was controlled in analyses. At exit, the IBI group had better outcomes in all measured areas, with milder autism severity, higher adaptive functioning, and higher cognitive skills. Younger initial age predicted better cognitive outcomes in the IBI group but not the Waitlist group. Higher initial adaptive skills predicted better outcomes similarly in the two groups. Results support the effectiveness of community-based IBI and suggest that earlier age at treatment onset may increase the likelihood of better outcomes relative to comparison conditions.