Eligible studies needed to include preschool children with a diagnosis of ASD or pervasive developmental disorder (PDD). Interventions were those that focused on applied behaviour intervention approaches to behavioural management and could be directed at the parents, caregivers or the child. Special educators, teachers, speech pathologists, psychologists or other allied professional students could deliver the intervention. Studies needed to be of preschool children (18 months to six years of age). Outcomes included cognitive, language or adaptive behaviour. Eligible study designs were trials (defined as systematic reviews [sic]), randomised controlled trials (RCTs), quasi-randomised controlled trials and controlled trials). Study duration was between 12 and 48 months. Intensity of the intervention varied between 18 and 39 hours weekly over one to three years. Where stated, intensity ranged between five hours and 31 hours weekly in the control groups.
Two authors assessed whether studies met the inclusion criteria.