The PD COMM trial: a protocol for the process evaluation of a randomised trial assessing the effectiveness of two types of SLT for people with Parkinson's disease.

Background: The PD COMM trial is a phase III multi-centre randomised controlled trial whose aim is to evaluate
the effectiveness and cost-effectiveness of two approaches to speech and language therapy (SLT) compared with
no SLT intervention (control) for people with Parkinson’s disease who have self-reported or carer-reported problems
with their speech or voice. Our protocol describes the process evaluation embedded within the outcome evaluation
whose aim is to evaluate what happened at the time of the PD COMM intervention implementation and to provide
findings that will assist in the interpretation of the PD COMM trial results. Furthermore, the aim of the PD COMM process
evaluation is to investigate intervention complexity within a theoretical model of how the trialled interventions might
work best and why.
Methods/design: Drawing from the Normalization Process Theory and frameworks for implementation fidelity, a mixed
method design will be used to address process evaluation research questions. Therapists’ and participants’ perceptions
and experiences will be investigated via in-depth interviews. Critical incident reports, baseline survey data from therapists,
treatment record forms and home practice diaries also will be collected at relevant time points throughout the running
of the PD COMM trial. Process evaluation data will be analysed independently of the outcome evaluation before the two
sets of data are then combined.
Discussion: To date, there are a limited number of published process evaluation protocols, and few are linked to trials
investigating rehabilitation therapies. Providing a strong theoretical framework underpinning design choices and being
tailored to meet the complex characteristics of the trialled interventions, our process evaluation has the potential to
provide valuable insight into which components of the interventions being delivered in PD COMM worked best (and
what did not), how they worked well and why.