Detailed statistical analysis plan for a guided self-determination intervention versus an attention control for outpatients with type 2 diabetes in the randomised OVERCOME trial

Background: Autonomy-supporting interventions may be a prerequisite to achieve better long-term management of type 2 diabetes. Evidence suggests that the guided self-determination (GSD) method might improve haemoglobin A1c and diabetes distress in people with type 1 diabetes. The evidence of an effect of a GSD intervention compared with an attention control group in adults with type 2 diabetes is unknown. Methods/design: The trial is designed as a pragmatic, investigator-initiated, dual-centre, randomised, parallel-group, assessor-blinded, superiority clinical trial of persons with type 2 diabetes. A nurse will administer GSD intervention versus an attention control. The primary outcome is diabetes distress, and secondary outcomes are quality of life, depressive symptoms, and non-serious adverse events. Exploratory outcomes are haemoglobin A1c, motivation, and serious adverse events. Participants are assessed at baseline, 5-, and 12-month follow-up. Here, we present a detailed, comprehensive plan of all statistical analyses, including methods to handle missing data, and assessments of the underlying statistical assumptions. The statistical analyses will be conducted independently by two statisticians following the present plan. Discussion: To mitigate the risk of analysis bias and increase the validity of the OVEROME trial, this statistical analysis plan was developed prior to unblinding of the trial results in concordance with the Declaration of Helsinki and the Conference on Harmonization of Good Clinical Practice Guidelines. Trial registration: ClinicalTrials.gov NCT 04601311. Registered on October 2020.