# Applying concepts of probability

If we try to apply this same concept of probability to lawyers' predictions about the outcome of specific cases, however, we immediately run into problems. Frequentist probability may play some role in predicting legal outcomes, but it is surely not the predominant concept of probability being used. For example, when taking on a criminal appeal, a lawyer might caution the client that less than ten percent of such cases are reversed on appeal. We would not expect the lawyer to base her own evaluation of the likelihood of reversal solely on the relative frequency of such reversals among all criminal appeals. We would expect her to evaluate the likelihood of success based on all the individual factors relating to that specific case: the nature of the evidence presented at trial, the strength of the legal issues on appeal, the reputation of the trial judge, and the appellate court's prior rulings on similar issues. The frequentist view of probability gives us no understanding of how probability can be applied to the assessment of a single unique event. Unless an event can be categorized as one instance of a general set or class of events, of which outcomes can be accurately measured and counted, the frequentist view of probability is inapplicable. 57 Yet individuals, and especially lawyers and judges, often make probability statements regarding the outcome of unique individual events, particularly lawsuits.58 If such lawyers are not talking about relative frequencies, then what are they talking about?

Most probability theorists would say that such statements reflect a personalist or subjective concept of probability.59 As the latter term implies, probability statements under this concept represent the degree of rational belief that the speaker holds about the likelihood of occurrence of the event in question. 60 Although such statements are not empirically verifiable in the way frequentist concepts are, they do have an objective correlative—the betting odds that the person holding the belief would be willing to give or accept as to the occurrence of the event. Accordingly, the difference between my saying that the Mets have a 10% chance to win the pennant and saying they have a 50% chance is the degree of my subjective belief that the Mets will in fact win the pennant. If I will accept an even-money bet that the Mets will win, then I have a stronger belief than if I demand odds of 9-1.

The subjective concept of probability enables us to make sense of probability statements about individual, nonrepeat events, and provides a mechanism (i.e., betting behavior) for formulating and understanding such probability statements.61 Utilizing the subjectivist concept of probability, we can also prescribe minimal standards of rationality with respect to beliefs about probability.

The subjectivist concept of probability, however, implies that an individual's subjective belief in an event's likelihood of occurrence is, in most instances, the only justification for any statement of probability. That is, if I assert that the Mets have a 99% likelihood of winning the pennant next year, then the statement is true insofar as I actually possess that degree of faith in the ultimate triumph of the Mets. The fact that everyone else thinks the statement highly implausible in no way refutes it, unless, of course, the knowledge that others disagree with me alters my subjective degree of belief. By the same token, the fact that two individuals disagree strongly about a probability judgment creates no inconsistency. Indeed, under a subjectivist view, it is hard to see what the disagreement is even about. If I assert that the Mets have a 99% chance of winning the pennant, and my colleague asserts it is a mere .5% chance (because the Cubs are the team of destiny in his view), then we are merely reporting on our different subjective states of belief, not disagreeing about any objective facts.

How well does the subjectivist concept of probability comport with the lawyer's activity of predicting future case outcomes? Quite well, at least in certain respects. It is certainly plausible to view many of the decisions lawyers make with respect to litigation and settlement as "bets," which reflect their degree of belief about the likelihood of the outcomes of particular, nonrepeat events. The subjectivist concept of probability captures that aspect of legal prediction and permits the application of a sophisticated mathematical analysis to the probabilities of single events.

What the subjectivist view does not provide is any justification, other than subjective belief and certain minimum rationality constraints, for the assignment of particular probabilities to particular events. If I believe that a case has a 10% likelihood of success, and you believe it has a 70% chance, then the subjectivist concept gives us no way of resolving the dispute, or even of explaining why it is a dispute and not merely a disparity of beliefs. Yet, surely two lawyers who reached such disparate conclusions about the likelihood of success on a case would (1) view the simultaneous assertion by two trained lawyers that the same case had a 10% and 70% of success as somehow involving inconsistent judgments, and (2) seek to resolve the inconsistencies through discussion of objective features of the case. In short, they would act as if the probability were to be determined by an analysis of objective features of the case and that consensus as to a "correct" probability were obtainable through such analysis.

The subjectivist view of probability does not deny that people reach their individual probability assessments through an analysis of the objective facts surrounding the event.63 Rather, it takes that as a brute fact of human behavior, and denies only the possibility that one can objectively evaluate the truth of such probability statements.64 The subjectivist view, similarly, does not deny the possibility that most people will agree in their assessments of the probabilities of most events.65 But there is nothing in the theory that would require such consensus to form, nor that provides any basis for criticizing or refuting anyone who held a dissenting view of the probability of the same event.

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