In New Mexico and many other jurisdictions, judges may detain defendants pretrial if the prosecutor proves, through clear and convincing evidence, that releasing them would pose a danger to the public. However, some policymakers argue that certain classes of defendants should have a “rebuttable presumption” of dangerousness, shifting the burden of proof to the defense. Using data on over 15,000 felony defendants who were released pretrial in a 4-year period in New Mexico, we measure how many of them would have been detained by various presumptions, and what fraction of these defendants in fact posed a danger in the sense that they were charged with a new crime during pretrial supervision. We consider presumptions based on the current charge, past convictions, past failures to appear, past violations of conditions of release, and combinations of these drawn from recent legislative proposals. We find that for all these criteria, at most 8% of the defendants they identify are charged pretrial with a new violent crime (felony or misdemeanor), and at most 5% are charged with a new violent felony. The false-positive rate, that is, the fraction of defendants these policies would detain who are not charged with any new crime pretrial, ranges from 71% to 90%. The broadest legislative proposals, such as detaining all defendants charged with a violent felony, are little more accurate than detaining a random sample of defendants released under the current system, and would jail 20 or more people to prevent a single violent felony. We also consider detention recommendations based on risk scores from the Arnold Public Safety Assessment (PSA). Among released defendants with the highest risk score and the “violence flag,” 7% are charged with a new violent felony and 71% are false positives. We conclude that these criteria for rebuttable presumptions do not accurately target dangerous defendants: they cast wide nets and recommend detention for many pretrial defendants who do not pose a danger to the public.

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审前危险性的可反驳推定有多准确？来自新墨西哥州的自然实验

在新墨西哥州和许多其他司法管辖区，如果检察官通过明确和令人信服的证据证明释放被告会对公众构成危险，则法官可以在审前拘留被告。然而，一些政策制定者认为，某些类别的被告应该有危险性的“可反驳推定”，将举证责任转移给辩护方。使用新墨西哥州 4 年内获释的 15,000 多名重罪被告的数据，我们衡量其中有多少人会因各种推定而被拘留，以及这些被告中有多少实际上构成了危险，即他们在审前监督期间被指控犯有新的罪行。我们考虑基于当前指控、过去的定罪、过去未能出庭、过去违反释放条件的推定，以及从最近的立法提案中得出的这些的组合。我们发现，对于所有这些标准，他们确定的被告中最多 8% 在审前被指控犯有新的暴力犯罪（重罪或轻罪），最多 5% 的被告被指控犯有新的暴力重罪。假阳性率，即这些政策将拘留的被告中没有被指控犯有任何新的预审罪行的比例，在 71% 到 90% 之间。最广泛的立法建议，例如拘留所有被控犯有暴力重罪的被告，比拘留随机抽样的在现行制度下获释的被告更准确，并且会监禁 20 人或更多人以防止单一的暴力重罪。我们还根据阿诺德公共安全评估 (PSA) 的风险评分考虑拘留建议。在风险评分最高和“暴力旗帜”的获释被告中，7% 被指控犯有新的暴力重罪，71% 是误报。我们的结论是，这些可反驳推定的标准并没有准确地针对危险的被告人：他们广撒网并建议拘留许多不会对公众构成危险的审前被告人。