BACKGROUND
The PD COMM trial is a phase III multi-centre randomised controlled trial that aims to evaluate the effectiveness and cost-effectiveness of two approaches to speech and language therapy (SLT) compared to no SLT intervention (control) for people with Parkinson’s disease who have self-reported or carer-reported problems with their speech or voice [1]. A process evaluation is underway alongside the PD COMM trial which aims to evaluate what went on at the time of the delivery of the trial interventions and to provide findings that will assist in the interpretation of the PD COMM trial results. This process evaluation will: 1) Investigate therapists’ experiences of delivering the PD COMM interventions, identifying the actual practices and likely tailoring that took place within the working context. 2) Investigate therapists’ familiarity with LSVT and NHS standard SLT, their methods and procedures. 3) Identify therapists’ learning over time and its potential impact on outcomes. 4) Explore therapists’ expectations in terms of intervention impacts and their research role.

METHODS
Drawing from the Normalization Process Theory [2] a mixed method design will be used to answer process evaluation research questions. Therapists’ perceptions, experiences and familiarity with the PD COMM interventions will be investigated via an online questionnaire and in-depth interviews. The interviews will be carried out at two time points: midway through therapists’ involvement in the trial and at the end of their involvement, once they have treated their last PD COMM participant. This will be essential in order to unpick the impact that learning over time might have on therapists’ role in delivering the PD COMM interventions. Also, all therapists will be asked to record key reflections in the form of ‘critical incident reports’. Treatment record forms and copies of therapy notes will also be collected at relevant time points throughout the running of the PD COMM trial.

RESULTS
The PD COMM trial is registered with the National Institute for Health Research Health Technology Assessment programme (HTA 10/135/02). ISRCTN: 12421382 (Registered 18 April 2016). To date 17 sites have opened. Participant recruitment and process evaluation data collection is underway.

CONCLUSION
This process evaluation will provide a valuable insight into how PD COMM therapists go about their everyday job whilst carrying out their research role. By developing a clear account of the challenges and experiences of therapists involved in complex interventions rehabilitation trials process evaluations can play a vital role in increasing the researcher’s understanding on why a complex intervention works or fails.