Observational study and trial designs
The observational study in all scenarios was simulated to be 5 years long with a baseline visit and annual follow-up visits.The trials were simulated to randomise participants in a 1:1 ratio to treatment or control. After a baseline visit, follow-up was by annual visits for either 5 years or 3 years, depending on the simulation scenario. All 5 years of the observational study were used to estimate the parameters for the sample size calculation, regardless of whether the proposed trial was 5 years or 3 years in length.In addition, the average variances and co-variances from the simulated observational studies from certain scenarios were used to consider samples sizes calculated for 2, 4, 6 and 7-year trials with annual visits.