Longitudinal Effects of Early Intensive Behavioural Intervention on Adaptive Functioning and Cognitive Development in Children with Autism Spectrum Disorder in South West Nigeria

This doctoral study examines the longitudinal effects of early intensive behavioural intervention on adaptive functioning and cognitive development in children with Autism Spectrum Disorder in South West Nigeria, generating original empirical evidence in a context characterised by near-total absence of published longitudinal intervention data. Early intensive behavioural intervention, typically involving forty or more hours per week of structured applied behaviour analytic instruction, has the strongest evidence base of any autism intervention for children under five in international literature, yet has never been evaluated in Nigerian settings. A randomised waitlist-controlled design is employed across three early intervention sites in Lagos, Ogun, and Oyo States, with sixty-four children randomly assigned to immediate treatment or a six-month delayed treatment condition. Adaptive functioning, cognitive development, language, and autism symptom severity are assessed at baseline, six months, twelve months, and twenty-four months using standardised international assessment tools. Linear mixed-effects models are used to analyse developmental trajectories, with disability severity and socioeconomic status as covariates. The study also documents implementation fidelity, caregiver training outcomes, and programme cost-effectiveness, providing a comprehensive evaluation package. Findings are expected to contribute the first randomised controlled trial data on early intensive behavioural intervention efficacy in Nigeria, with significant implications for national early intervention policy and investment decisions. Recommendations address sustainable delivery models appropriate to Nigerian resource contexts. Keywords: early intensive behavioural intervention, autism, longitudinal study, randomised controlled trial, South West Nigeria.