Laurence Tribe: Maths on Trial (4)

Tribe’s reaction to standard objections to math on trial

In the last post we gave a description of the first part of Tribe’s seminal article:

Firstly, a description of the kind of use of mathematics at trial that he is specifically going to discuss, with examples.

Today we will summarize his arguments in the second part.

Secondly, a review of the traditional arguments that judges have used against mathematics at trial, together with Tribe’s reaction to these arguments;

He lists objections that have been made by judges to the introduction of statistical evidence at trial, some of which has actually been written into law.

Objection 1: At first glance, probability concept might appear to have no application in deciding precisely what did or did not happen on a specific prior occasion: either it did or it didn’t – period.

Tribe’s reaction: Although this is true in itself, the statistical knowledge can be very useful in cases where it is used in conjunction with sufficient further information.

Objection 2: Making use of the mathematical information available first requires transforming it from evidence about the generality of cases to evidence about the particular case; some feel that no such translation is possible.

Tribe’s reaction: this kind of information is important for the trier of fact to come to a decision about the likelihood of certain events, for instance the “4/5” probability that the blue bus that hit the plaintiff belonged to the defendant who was responsible for operating 4/5 of the blue buses in town.

Objection 3: In very few cases, if any, can the mathematical evidence, taken alone and in the setting of a completed lawsuit, establish the proposition to which it is directed with sufficient probative force to prevail.

Tribe’s reaction: But the fact that mathematical evidence taken alone can rarely, if ever, establish the crucial proposition with sufficient certitude to meet the applicable standard of proof does not imply that such evidence – when properly combined with other, more conventional, evidence in the same case – cannot supply a useful link in the process of proof…The real issue is whether there is any acceptable way of combining mathematical with non-mathematical evidence. If there is, mathematical evidence can indeed assume the role traditionally played by other forms of proof.

Now, it is a fact that many mathematicians and statisticians have proposed a way to integrate mathematics and traditional evidence, based on Bayes’ theorem. In fact, Tribe’s whole article actually was written as a response to an article on the use of Bayes’ theorem at trial, authored by Finkelstein and Fairley (we’ll investigate this and similar articles in future posts). In the third part of Tribe’s article, he briefly summarizes the point of view of those who advocate using Bayes’ theorem at trial. This will be the subject of the next post