Effectiveness and experiences of early intensive behavioral and naturalistic developmental behavior interventions for autism spectrum disorders: a mixed-methods systematic review and meta-analysis

Background: Autism spectrum disorder (ASD) is a neurodevelopmental condition marked by social communication deficits and restricted, repetitive behaviors. Among evidence-based practices (EBPs), interventions grounded in applied behavior analysis (ABA) principles—including Early Intensive Behavioral Intervention and naturalistic developmental behavioral interventions—are widely used. While the evidence suggests potential benefits, the findings are inconsistent, most studies carry a high risk of bias, and the quality of evidence is generally low to very low. Gaps also remain in comparisons with treatment as usual (TAU) and across intervention intensities. Aims: This mixed-methods systematic review and meta-analysis evaluated the quantitative effectiveness and qualitative experiences of ABA-based interventions for children and adolescents with ASD, addressing the methodological limitations of earlier studies, and examining comparisons with TAU. Methods: Seven databases were searched up to August 2023 following the PRISMA guidelines. Twenty-five studies met the inclusion criteria (16 randomized controlled trials, 9 qualitative). The quantitative outcomes included adaptive behavior, cognitive ability (IQ/DQ), language, daily living skills, socialization, joint attention, and autism symptom severity. Qualitative studies explored parents’ and practitioners’ experiences. Random-effects models were used, with subgroup analyses by intervention intensity and TAU comparisons. Results: The meta-analysis revealed significant improvements in adaptive behavior (SMD = 0.31, 95% CI: 0.04–0.59, GRADE = low), daily living skills (SMD = 0.36, 95% CI: 0.08–0.64, GRADE = low), language skills (SMD = 0.42, 95% CI: 0.24–0.60, GRADE = moderate), and joint attention behavior (SMD = 0.27, 95% CI: 0.04–0.49, GRADE = low) compared with the controls. High-intensity interventions had a notably greater effect on language skills (SMD = 0.72, 95% CI: 0.42–1.01) than low-intensity interventions (SMD = 0.34, 95% CI: 0.13–0.55). Comparisons with TAU revealed significant effects on adaptive behavior (SMD = 0.34, 95% CI: 0.02–0.66), daily living skills (SMD = 0.39, 95% CI: 0.07–0.71), and language skills (SMD = 0.51, 95% CI: 0.24–0.78). Qualitative findings highlighted perceived family and practitioner benefits but also barriers such as financial constraints and variability in training quality. Conclusion: This study confirms the effectiveness of ABA in improving developmental and behavioral outcomes in children with ASD. However, systemic challenges and variability in outcomes underscore the need for targeted policy initiatives, enhanced training programs, and further research on the impact of ABA on core ASD symptoms.