Better Outcomes for Older people with Spinal Trouble (BOOST) Trial: statistical analysis plan for a randomised controlled trial of a combined physical and psychological intervention for older adults with neurogenic claudication

Neurogenic claudication is a common spinal condition affecting older adults that has a major effect on mobility and implicitly independence. The effectiveness of conservative interventions in this population is not known. We describe the statistical analysis plan for the Better Outcomes for Older people with Spinal trouble (BOOST) randomised controlled trial. BOOST is a pragmatic, multicentre, parallel, two-arm, randomised controlled trial. Participants are community-dwelling adults, 65 years or older, with neurogenic claudication, registered prospectively, and randomised 2:1 (intervention to control) to the combined physical and psychological BOOST group physiotherapy programme or best practice advice. The primary outcome is the Oswestry Disability Index at 12 months. Secondary outcomes include the Short Physical Performance Battery, Swiss Spinal Stenosis Scale, 6 Minute Walk Test, Fear Avoidance Beliefs Questionnaire, and Tilburg Frailty Indicator. Outcomes are measured at 6 and 12 months by researchers blinded to treatment allocation. The primary statistical analysis is by intention to treat. Further study design details are published in the BOOST protocol. The planned statistical analyses for the BOOST trial aim to reduce the risk of outcome reporting bias from prior data knowledge. Any changes or deviations from this statistical analysis plan will be described and justified in the final study report. This study has been registered in the International Standard Randomised Controlled Trial Number registry, reference number ISRCTN12698674 . Registered on 10 November 2015.