prior probability

Not that Holmes. This one. In our previous blog post (11/14/14), we promised to explain why our defense of Bayesian methods is relevant to law. After all, how is probability theory generally or any of the foregoing specifically — i.e. Hájek’s analysis of the reference class problem, his critique of radical subjectivism, and our critique of Hájek’s critique — relevant to law? In short, probability theory, Hájek’s paper, and our critique of Hájek are relevant to law in many ways.

Consider, for example, the close relation between the reference class problem and legal reasoning, especially the doctrine of binding precedent and the legal principle that “like cases should be treated alike.” A general principle in common law legal systems is that similar cases should be decided the same way so as to give similar and predictable outcomes, and the doctrine of precedent is the mechanism by which this goal is attained. A precedent is thus a principle or rule established in a previous legal case that is binding on a court or other tribunal when deciding subsequent cases with similar issues or facts.

But in order to determine whether the facts of one case are substantially similar to those in a previous case, we must engage in reasoning by analogy, and the reference class problem infects legal reasoning or reasoning by analogy because no two cases or sets of cases will be identical in all their particulars. In other words, if we are asked to determine whether case A is similar to case B, we must first determine whether case A and case B are in the same reference class. The problem, however, is that any given case may be incorporated in many possible reference classes. Continue reading →