Proportionate action requires a decision rule

The recent Editorial on youth suicide prevention in the Americas argues that emerging evidence is no reason to postpone proportionate action.1 We agree. Proportionality, however, remains to be specified as a decision rule. This matters because youth suicide exemplifies an evidence paradox: the populations at greatest risk are often those in whom definitive trials are hardest to conduct.2 The unresolved question is therefore what evidentiary threshold should justify action when both intervention and inaction can cause harm.