Bail reform is gaining momentum nationwide. Reformers aspire to untether pretrial detention from wealth (the ability to post money bail) and condition it instead on statistical risk, particularly the risk that a defendant will commit crime if he remains at liberty pending trial. The bail reform movement holds tremendous promise, but also forces the criminal justice system to confront a difficult question: What statistical risk that a person will commit future crime justifies short-term detention? What about lesser restraints, like GPS monitoring? Although the turn to actuarial risk assessment in the pretrial context has engendered both excitement and concern, the debate so far has largely ignored this foundational question. One way of think...