TABLE 1.

Operating characteristics used in this paper and their definitions

Name	Definition
PCP	“Per‐Cohort‐Power,” the ratio of the sum of true positives among the sum of truly efficacious cohorts (i.e., the sum of true positives and false negatives) across all platform trial simulations, that is, the probability of a true positive decision for any new cohort entering the trial. This is a measure of how wasteful the trial is with superior therapies.
PCT1ER	“Per‐Cohort‐Type‐1‐Error,” the ratio of the sum of false positives among the sum of all truly not efficacious cohorts across all platform trial simulations, that is, the probability of a false positive decision for any new cohort entering the trial. This is a measure of how sensitive the trial is in detecting futile therapies.
FWER	“Family‐wise type 1 Error Rate”, the proportion of platform trials, in which at least one false positive decision has been made (i.e., probability of at least one false positive decision across all cohorts), where only such trials are considered, which contain at least one cohort that is in truth futile. Formal definition: $\frac{1}{\mid I_0^{*}\mid }{\sum }_{i\in I_0^{*}}\text{𝟙}\left\{{\mathit{FP}}_i>0\right\}$, where $I_0^{*}=\left\{i\in \left\{1,\dots \mathit{\text{iter}}\right\}:n_i^{H0}>0\right\}$, where iter is the number of platform trial simulation iterations, FP i denotes the number of false‐positive decisions in simulated platform trial i and $n_i^{H0}$ is the number of not efficacious cohorts in platform trial i.
FWER BA	“Family‐wise type 1 Error Rate Bayesian Average”, the proportion of platform trials, in which at least one false positive decision has been made (i.e., probability of at least one false positive decision across all cohorts), regardless of whether or not any cohorts which are in truth futile exist in these trials. Formal definition: $\frac{1}{\mathit{\text{iter}}}{\sum }_{i=1}^{\mathit{\text{iter}}}\text{𝟙}\left\{{\mathit{FP}}_i>0\right\}$, where iter is the number of platform trial simulation iterations and FP i denotes the number of false‐positive decisions in simulated platform trial i. This will differ from FWER in scenarios where—due to a prior on the treatment effect—in some simulation runs, there are by chance only efficacious cohorts in the platform trial (see Appendix A.3 for more details on the different treatment efficacy scenarios).
Disj Power	“Disjunctive Power”, the proportion of platform trials, in which at least one correct positive decision has been made (i.e., probability of at least one true positive decision across all cohorts), where only such trials are considered, which contain at least one cohort that is in truth superior. Formal definition: $\frac{1}{\mid I_1^{*}\mid }{\sum }_{i\in I_1^{*}}\text{𝟙}\left\{{\mathit{TP}}_i>0\right\}$, where $I_1^{*}=\left\{i\in \left\{1,\dots \mathit{\text{iter}}\right\}:n_i^{H1}>0\right\}$, where iter is the number of platform trial simulation iterations, TP i denotes the number of true‐positive decisions in simulated platform trial i and $n_i^{H1}$ is the number of efficacious cohorts in platform trial i.
Disj Power BA	“Disjunctive Power Bayesian Average”, the proportion of platform trials, in which at least one correct positive decision has been made (i.e., probability of at least one true positive decision across all cohorts), regardless of whether or not any cohorts which are in truth superior exist in these trials. Formal definition: $\frac{1}{\mathit{\text{iter}}}{\sum }_{i=1}^{\mathit{\text{iter}}}\text{𝟙}\left\{{\mathit{TP}}_i>0\right\}$, where iter is the number of platform trial simulation iterations and TP i denotes the number of true‐positive decisions in simulated platform trial i. This will differ from Disj Power in scenarios where—due to a prior on the treatment effect—in some simulation runs, there are by chance no efficacious cohorts in the platform trial (see Appendix A.3 for more details on the different treatment efficacy scenarios).