Statistical analysis
dementia, disability, a disability
REGRESSION, SECONDARY
For the primary outcome of difference in disability assessment for dementia score between groups, an analysis of covariance was conducted using stratification variables (site, co-resident carer, and history of falls) and baseline disability assessment for dementia score as covariates. For secondary outcome measures, analyses of covariances were conducted, using the stratification and respective baseline measures as covariates. All analyses were done on an intention-to-treat basis, although data were only available for people who completed the outcome assessment. For the main analysis, multiple imputation using chained equations was used when <40% of the data were missing and data were not missing completely at random. Number of imputations was based on proportion of missing data for the outcome. The imputation models included the randomisation stratification variables, participant’s baseline characteristics, and scores at baseline. Imputation was done overall rather than separately by randomised group. Results for the imputed dataset were pooled using Rubin’s rule. Effect sizes were standardised as Cohen’s d.Multiple sensitivity analyses were conducted: including complete cases; including those who had completed the trial before the covid-19 pandemic; using the interim data collected in the early weeks of the pandemic; correcting for survivor bias, by assigning a disability assessment for dementia score of zero to participants who died; excluding those who terminated the intervention early owing to the pandemic; and excluding three participants who had Montreal cognitive assessment scores at baseline above the upper limit.Falls were analysed as the proportions of participants who fell, the incidence rate ratio using a negative binomial regression, and time to first fall using a Cox proportional hazards regression. We anticipated that any impact of the PrAISED intervention on falls would not be immediate, so our predefined efficacy outcome was rate of falling between months 4 and 15. Only participants with a complete series of calendar returns were included.The statistical analysis plan is available, including further details of imputation methods.