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

Abstract

BackgroundThere 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.MethodsOf 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.ResultsGood 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.ConclusionsEarly 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.

Debate: Neurodiversity, autism and healthcare

“…This could enable early triage into discussion of evidenced pre-emptive support prior to formal diagnosis. Optimising the child's early dyadic social communication and engagement within the family proves to be the intervention effect that best mediates subsequent long-term benefits in autistic child development (Carruthers et al, 2023). Intervention science now shows how this can reliably be done.…”

Mediation of meaningful outcomes in early intervention: a commentary on Carruthers et al. (2023)

“…However, if we apply a developmental lens, it is appropriate to look for intervention effects on skills that are developmentally first in line for change before we can expect movement in more distal developmental outcomes. We see this logic applied by Carruthers et al (2023), where increases in children's initiations (an indicator of children's social communicative development) in the context of a parent-child interaction is examined as the candidate mediator of change in the distal broader assessment of social communication and social skills obtained from the severity score of the ADOS-2. Although this theory of change that moves from parent behavior to change in child behavior in the context of parent-child interaction and then to broader child behavior is hypothesized across many caregiver-mediated intervention approaches, few have empirically tested this theory.…”

“…As noted by Carruthers et al. (2023), the use of a diagnostic assessment (ADOS‐2) as an outcome measure can be viewed as a focus on deficits and it is also not clear how such a measure captures skill growth. Building social communication skills is a common goal across early intervention approaches but difficult to measure.…”

“…Carruthers et al. (2023) place an important focus on the generalization of children's skills to other contexts and people. A question emerges regarding the degree to which we can expect to see an impact of a brief intervention on measures that capture relevant but distal outcomes.…”

“…Carruthers et al. (2023) also explore another novel aspect of mediation by proposing candidate moderators of the intervention mechanism. Candidate moderators included baseline nonverbal age‐equivalent scores of cognition from the visual reception and fine motor subscales of the Mullen Scales of Early Learning, scores of parent‐reported communication and symbolic development from the Communication and Symbolic Behavior Scales Developmental Profile, and insistence on sameness from the Autism Diagnostic Interview‐Revised.…”