Dangerous Decisions: An Essay on the Mathematics of Clinical Violence Prediction and Involuntary Hospitalization

Abstract

This Article has two major purposes. First, it provides a mathematicaldescription of an ideal procedure for making clinical decisions about patients\u27future violence, a description that provides a context for evaluating clinicians\u27 dangerousness decisions. For purposes of illustration, the Article uses a specific clinical situation-deciding whether to hospitaize involuntarily a patientbased on his risk of harming another. The Article argues that the decisioninvolves balancing potential risks to third parties (often the patient\u27s familymembers) with the massive deprivation of liberty and other potentialharms to the patient that could result from confinement. The mathematicaldescription of the decision procedure consists of a comprehensive method fordescribing the accuracy of predictions or prediction instruments, a methodfor assigning values to correct and incorrect predictions, a method foradjusting predictions based on those values, and-most importantly-an explicit means for expressing uncertainty in those values. Second, the Article evaluates the actual impact of uncertainty on an idealdecision procedure. When we combine our uncertainty about moral valuationsof right and wrong decisions, our uncertainty about base rates, and ouruncertainty about the relevant time periods over which predictions shouldapply, what results is an uncertainty about the correctness of prediction-baseddecisions that makes most criticism of those decisions untenable. ThisArticle shows that our uncertainty about the factors intrinsic to a hypothetical,best-case prediction procedure usually would preclude valid post hoc criticismof wrong decisions about dangerousness; a fortiori, most real-life predictionerrors also should be beyond criticism