Statistical methods
The rate of disagreement between site assessments and central assessments of PFS was calculated, and the sensitivity of analysis results to switching between site-assessed versus centrally assessed PFS was assessed by evaluating the magnitude of the change to the estimated hazard ratios (HRs).A series of simulations were performed to explore what effect measurement error may have on a trial with similar characteristics. A set of 10,000 simulated trials were generated for a range of scenarios, which differed according to the specified magnitude of the underlying treatment effect and the type (non-differential/differential) and intensity of the measurement error imposed. Each simulated trial comprised 150 participants randomly allocated in a 2:1 ratio active drug (ACTIVE) versus placebo (PBO), who were followed until all observations of PFS were complete (i.e. no censored observations).PFS times in each simulation were generated from an exponential distribution with a median of 4 weeks for the PBO group. The median PFS for the ACTIVE group was calculated by applying a series of hypothetical HRs to the PBO exponential distribution. Separate simulations used hypothetical HRs of 0.6, 0.67 or 0.75.Non-differential measurement error was introduced into each simulation by shifting the true PFS time of a random proportion of Differential measurement error was imposed by adding 4 weeks to the true PFS time for a random proportion (q) of participants in the ACTIVE group and subtracting 4 weeks from the true PFS time for a random proportion of 