We evaluated the clinical and cost-effectiveness of manualised sensory integration therapy (SIT) for autistic children with sensory processing difficulties in a two-arm randomised controlled trial. Trial processes and contextual factors which may have affected intervention outcomes were explored within a nested process evaluation. This paper details the process evaluation methods and results. We also discuss implications for evaluation of individual level, tailored interventions in similar populations.
The process evaluation was conducted in line with Medical Research Council guidance. Recruitment, demographics, retention, adherence, and adverse effects are reported using descriptive statistics. Fidelity of intervention delivery is reported according to the intervention scoring manual. Qualitative interviews with therapists and carers were undertaken to explore the acceptability of the intervention and trial processes. Qualitative interviews with carers explored potential contamination.
Recruitment, reach and retention within the trial met expected thresholds. One hundred thirty-eight children and carers were recruited (92% of those screened and 53.5% of those who expressed an interest) with 77.5% retained at 6 months and 69.9% at 12 months post-randomisation. The intervention was delivered with structural and process fidelity with the majority (78.3%) receiving a ‘sufficient dose’ of intervention. However, there was considerable individual variability in the receipt of sessions. Carers and therapists reported that trial processes were generally acceptable though logistical challenges such as appointment times, travel and COVID restrictions were frequent barriers to receiving the intervention. No adverse effects were reported.
The process evaluation was highly valuable in identifying contextual factors that could impact the effectiveness of this individualised intervention. Rigorous evaluations of interventions for autistic children are important, especially given the limitations such as limited sample sizes and short-term follow-up as faced by previous research. One of the challenges lies in the variability of outcomes considered important by caregivers, as each autistic child faces unique challenges. It is crucial to consider the role of parents or other caregivers in facilitating access to these interventions and how this may impact effectiveness.
This trial is registered as ISRCTN14716440. August 11, 2016.

© 2024. The Author(s).