Challenges in reaching patients with severe mental illness for trials in general practice—a convergent mixed methods study based on the SOFIA pilot trial

Background Patients with severe mental illness (SMI) die prematurely due to undetected and inadequate treatment of somatic illnesses. The SOFIA pilot study was initiated to mend this gap in health inequity. However, reaching patients with SMI for intervention research has previously proven difficult. This study aimed to investigate the recruitment of patients with SMI for the SOFIA pilot study in 2021. Methods We used a mixed-method convergent design. The qualitative material comprised 20 interviews with general practitioners (GPs) and staff, during patient recruitment. The quantitative data consisted of process data on baseline characteristics, GPs reported reasons for excluding a patient, reported reasons for patients declining participation, and registered data from a Danish population of patients with SMI. We used thematic analysis in the qualitative analysis and descriptive statistics for the quantitative analysis. Pillar integration was used for integrating the material. Results Our findings show that selection bias occurred in the pilot study. We describe four main themes based on the integrated analysis that highlights selection issues: (1) poor data quality and inconsistency in defining severity definitions troubled identification and verification, (2) protecting the patient and maintaining practice efficiency, (3) being familiar with the patient was important for a successful recruitment, and (4) in hindsight, the GPs questioned whether the target population was reached. Conclusions In the light of theories of professions and street-level bureaucracy, we find that the main drivers of the patient selection bias occurring in the SOFIA pilot study were that 1) GPs and staff mended eligibility criteria to protect certain patients and/or to minimize workload and maintain efficiency in the practice 2) the data from the GP record systems and the digital assessment tool to assist recruitment was not optimal. Interventions targeting this patient group should carefully consider the recruitment strategy with a particular focus on professionals' discretionary practices and information technology pitfalls. Trial registration The pilot trial protocol was registered on the 5th of November 2020. The registration number is NCT04618250. Keywords: Trial recruitment, Severe mental illness, Pilot and feasibility studies, General practice, Mixed methods study