Somebody sent this through as a comment. I hope Don Mathias doesn't mind me using it, I will remove it if so. It deals with the misapprehension abroad that Ian Binnie wouldn't have looked at the evidence as a complete picture, but also in isolation where in his report he put some issues aside. It would not be possible to not look at the complete 'picture' in over 10,000 pages it would have been a repetitive theme and something needed to be taken into context when considering individual points. It also highlights that Fisher did not comment on whether Binnie's decisions were right or wrong.
Bain, Binnie, Fisher, Bayes – how should judges reach conclusions?
Posted on December 15, 2012 by Don Mathias
Once again out little nation is divided over the Bain case and its consequences. The current controversy is over whether the report by retired Canadian Supreme Court Justice Ian Binnie should be accepted or whether its review by retired New Zealand High Court judge Dr Robert Fisher QC has cast doubt on its conclusions.
We have seen here recently how appellate judges on the same court can differ sharply over what conclusions can be drawn from the evidence in a case. Is there a right way to arrive at conclusions from facts?
In trials juries are given little guidance on how to reason, other than being told that the drawing of inferences is a process of using logic and common sense, something people do all the time in their daily lives. It is assumed that people have an innate ability to reach proper conclusions. This assumption must be correct. We tend to be right more often than we are wrong, but without examining why.
Judges have to give reasons for their decisions. The process of articulating reasons imposes a discipline on judicial thinking, and until that process is completed a judge may not know what conclusion is going to be reached. An echo of this is the instruction to jurors to keep an open mind while evidence is being given.
Bayesian analysis is useful in revealing or guarding against errors of logic when inferences are drawn from facts. Dr Fisher has used this in his report. This does not mean that Ian Binnie was wrong to not use it in his. Most people have no idea what Bayes’ Theorem is and they infer correct conclusions without using it. The interesting question is whether Dr Fisher has revealed any error of logic that was sufficient to make Ian Binnie’s conclusions wrong.
My assessment is that the only candidate for being an error of this significance is Dr Fisher’s claim that Ian Binnie failed to consider the evidence cumulatively as opposed to by taking each item at a time. Ian Binnie has denied, in an email to the Minister of Justice that has been published, that he made this error.
It would be astonishing if Ian Binnie had made this mistake. Judges habitually stand back after evaluating the probative value of particular facts and look at the overall picture. That is done to enable a conclusion to be drawn from the combination of the probative values of the facts. This process is what is done instinctively when people exercise their judgment.
There are all kinds of influences, revealed by psychologists, which can cause people to make mistakes. A Bayesian approach to inference drawing can counteract those, but its best application requires extensive statistical information, far beyond what is usually available in court cases.
Nearly all judicial decisions are made only on the balance of probabilities. This standard recognises that we can seldom be certain we are right, and that in the interests of finality a decision on the balance of probability is good enough. Hugely important decisions are regularly made in the courts on that basis.
It is significant that Dr Fisher has not endeavoured to decide whether Ian Binnie’s conclusions were right or wrong, but that he correctly restricted his report to Ian Binnie’s method. Plainly, if Dr Fisher were to go further in a subsequent report, he would apply the Bayesian approach. But that should lead to the same conclusions that Ian Binnie reached unless radically inappropriate assessments of likelihood were made by Ian Binnie over critical facts to such an extent as to influence the result of considering the combined probative values of all the relevant facts.
I was surprised when reading Ian Binnie’s report at how he treated the evidence of the luminol footprints. Depending on the length of those footprints, they could have removed the case from being an exercise in assessing probabilities and made this a case of direct evidence of innocence. That was recognised in the Privy Council hearing, as both sides agree. However Ian Binnie has been generous to the prosecution by recognising some doubt over the accuracy of the measurement made by the police officer of the footprints on the carpet at the scene. Whether the measurement could really have been susceptible to error to an extent sufficient to cast doubt on who left it there is a matter of judgment for those who have looked at the evidence that was given on this point.
