Supplementary Material for: Statistical Analysis Plan for the INTEnsive ambulance-delivered blood pressure Reduction in hyper-ACute stroke Trial (INTERACT4).

Introduction: Recruitment is complete in the fourth INTEnsive ambulance-delivered blood pressure Reduction in hyper-ACute stroke Trial (INTERACT4) is a multicenter, prospective, randomized, open-label, blinded endpoint assessed trial of pre-hospital blood pressure (BP) lowering initiated in the ambulance for patients with a suspected acute stroke and elevated BP in China. According to the registered and published trial protocol and developed by the blinded trial Steering Committee and Operations team, this manuscript outlines a detailed statistical analysis plan for the trial prior to database lock. Methods: Patients were randomized (1:1) to intensive (target systolic BP [SBP] 130-140 mmHg within 30 minutes) or guideline-recommended BP management (BP lowering only considered if SBP >220 mmHg) group. Primary outcome is an ordinal analysis of the full range of scores on the modified Rankin scale at 90 days. A modified sample size of 2320 was estimated to provide 90% power to detect a 22% reduction in the odds (common odds ratio of 0.78) of a worse functional outcome using ordinal logistic regression, on the assumption of 5% patients with missing outcome and 6% patients with a stroke mimic. Conclusion: The statistical analysis plan for the trial has been developed to ensure transparent, verifiable, and prespecified analysis, and to avoid potential bias in the evaluation of the trial intervention.