Mediation of 6-year mid-childhood follow-up outcomes after pre-school social communication (PACT) therapy for autistic children: randomised controlled trial

Abstract

Background: There are very few mechanistic studies of the long-term impact of psychosocial interventions in childhood. The parent-mediated Paediatric Autism Communication Therapy (PACT) RCT showed sustained effects on autistic child outcomes from pre-school to mid-childhood. We investigated the mechanism by which the PACT intervention achieved these effects.

Methods: Of 152 children randomised to receive PACT or treatment as usual between 2 and 5 years of age, 121 (79.6%) were followed 5-6 years after the endpoint at a mean age of 10.5 years. Assessors, blind to the intervention group, measured Autism Diagnostic Observation Scale Calibrated Severity Score (ADOS CSS) for child autistic behaviours and Teacher Vineland (TVABS) for adaptive behaviour in school. Hypothesised mediators were child communication initiations with caregivers in a standard play observation (Dyadic Communication Measure for Autism, DCMA). Hypothesised moderators of mediation were baseline child non-verbal age equivalent scores (AE), communication and symbolic development (CSBS) and 'insistence on sameness' (IS). Structural equation modelling was used in a repeated measures mediation design.

Results: Good model fits were obtained. The treatment effect on child dyadic initiation with the caregiver was sustained through the follow-up period. Increased child initiation at treatment midpoint mediated the majority (73%) of the treatment effect on follow-up ADOS CSS. A combination of partial mediation from midpoint child initiations and the direct effect of treatment also contributed to a near-significant total effect on follow-up TVABS. No moderation of this mediation was found for AE, CSBS or IS.

Conclusions: Early sustained increase in an autistic child's communication initiation with their caregiver is largely responsible for the long-term effects from PACT therapy on autistic and adaptive behaviour outcomes. This supports the theoretical logic model of PACT therapy but also illuminates fundamental causal processes of social and adaptive development in autism over time: early social engagement in autism can be improved and this can have long-term generalised outcome effects.

Keywords: Autism spectrum disorder; developmental psychopathology; early intervention; mediation; structural equation modelling.

Figure 1

Parsimonious pre‐specified model of partial mediation of PACT therapy. Squares are observed variables, ovals are latent variables, double‐headed arrows indicate correlation and single‐headed arrows are direct effects. Single‐headed arrows lacking an origin indicate measurement errors. Dashed line D is the non‐mediated direct effect of treatment on the outcome at follow‐up, while paths A, B and C fall on paths of indirect effects between treatment and outcome at follow‐up [Color figure can be viewed at wileyonlinelibrary.com]

Figure 2

Standardised structural path coefficients (standard errors): top panel autism symptom behaviours (ADOS CSS), bottom panel adaptive functioning (VABC) (parent reported adaptive functioning at baseline, teacher reported adaptive functioning at endpoint and follow‐up). Squares are observed variables, ovals are latent variables, double‐headed arrows indicate correlation. and single‐headed arrows are direct effects. Dashed line D is the non‐mediated direct effect of treatment on the outcome at follow‐up, while paths A, B and C fall on paths of indirect effects between treatment and outcome at follow‐up. The coefficients for paths A and D from binary treatment a STDY, all others STDXY [Color figure can be viewed at wileyonlinelibrary.com]