Table 3.

Simulation setup based on IMpassion130³³.

Parameter	Values
Experimental treatment effect: Hazard ratio between experimental and control arms of trial (HRExp)	0.70 (More effective than expected) 0.78 (Target HR, i.e. alternative hypothesis) 0.85 (Less effective than expected) 1.00 (No treatment effect)
Residual bias: Hazard ratio between real-world controls and randomized controls after careful alignment on I/E criteria, covariate balancing, and alignment of endpoints, index dates, and follow-up time (HRRWD) (composite bias)	Range from 0.5 to 2 by 0.1 (i.e. 0.5, 0.6, …, 1.9, 2.0): 0.5 (Extreme): External patients have longer median time-to-event than randomized controls 1 (No bias) 2 (Extreme): External patients have shorter median time-to-event than randomized controls
Expected downweighting factor for external controlsa	0.6
Total number of patients in RCT (control + experimental)	675 (out of 900 planned in IMpassion130)
Number of external patients potentially available to borrow	375 (resulting in an expected 375 * 0.6 = 225 effectively borrowed external patients)
Randomization ratio in trial	2:1 (experimental:control)
Target number of events (control + experimental + downweighted external control)	655
Percent lost to follow-up in both the trial and external data source	5%
Accrual rate in trial	34 patients per month
Significance level for hypothesis test of experimental treatment effect	0.025 one-sided

^aAt the time of study design, the downweighting factor is known with certainty if using a power prior model with fixed power parameter, and is predicted if using a dynamic borrowing method.