Process evaluation of a New psychosocial goal-setting and manualised support intervention for Independence in Dementia (NIDUS-Family)

Introduction We report a process evaluation embedded within a UK Randomised Controlled Trial (RCT), which demonstrated that New Interventions for independence in Dementia Study (NIDUS)-Family (a manualised, multimodal psychosocial intervention), was effective relative to usual care, on the primary outcome of Goal Attainment Scaling (GAS) over one year. We aimed to test and refine a hypothesised theory of change model delineating key causal assumptions for impact mechanisms. Methods In 2021-22, intervention-arm dyads completed an acceptability questionnaire developed to test causal assumptions. We interviewed dyads and their intervention facilitators, purposively selected for diverse follow-up GAS scores and sociodemographic diversity. Matching observational data were collected from intervention session recordings, using a checklist developed to test causal assumptions. We thematically analysed data, then integrated qualitative and quantitative data. Results 174/204 (85.3%) dyads allocated to NIDUS-Family, fully completed the intervention, 18 partially completed it, while 12 received none. 47/192 (24.5%) of carers receiving any sessions completed the acceptability questionnaire. 27/58 (47%) dyads purposively selected, and 9/10 facilitators participated in qualitative interviews; and we observed 12 sessions. We identified four themes: A) Someone to talk to helps dyads feel supported; B) NIDUS-Family helps carers change their perspective; C) Personalisation helps people living with dementia maintain their identity; and D) Small steps help dyads move forward. Conclusion Key causal pathway mechanisms were: regular sessions with a consistent facilitator providing space to discuss priorities, supporting carers to consider new perspectives and approaches to personalising care; and planning small actionable steps towards goals. Findings will support NIDUS-Family implementation. ### Competing Interest Statement The authors have declared no competing interest. ### Clinical Trial ISRCTN11425138; IRAS project ID: 271363 ### Funding Statement This work is carried out within the UCL Alzheimers Society Centre of Excellence (grant 300) for Independence at home, NIDUS programme ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethical approval was received from Camden & Kings Cross Research Ethics Committee (REC). Study reference: 19/LO/1667 I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors