Ruminate on this!

No doubt you enjoy puzzles:

There is a group of animals, one third of which are sheep. One animal was examined and found to have four legs. The scientist who did that examination tells us that the result “four legs” was three times more likely if the examined animal was a sheep than if it was not a sheep. What is the probability that the examined animal was a sheep?

Most trial lawyers should be able to correctly answer that almost instantly. I have posted the answer in my comment on my alternative site.


Legitimate presuppositions about guilt and innocence

Before the evidence involving the defendant’s acts in a case is considered an assumption may be made about the likelihood that the defendant is guilty. This is different from the presumption of innocence, which simply means that the prosecutor must prove that the defendant is guilty and that the defendant does not have to prove innocence (see R v Wanhalla 24/8/06, CA321/05, [2007] 2 NZLR 573, (2006) 22 CRNZ 843 at [49], mentioned here on 25 August 2006). But – at least on a mathematical approach to conditional probabilities – there must be some starting assumption about whether the defendant is guilty in order that the effect of evidence can be determined. The ultimate decision, the verdict, will depend on how the evidence has affected the prior likelihood of guilt.

The “priors” can be expressed as a likelihood of guilt compared to a likelihood of innocence, each assessed before the evidence as to what the defendant did is considered. A ratio of probabilities is the same way of expressing this comparison of likelihoods. Are there appropriate numbers for making this comparison?

For some people – in the absence of evidence on the point given at trial – a starting point may be that a probability of guilt of 0.02 (that is, two chances out of a hundred), and a corresponding probability of innocence of 0.98, are a good way of reflecting the need to be fair. Almost certainly innocent, but recognising that there could be room for error about that, seems like a fair starting point. This might be the same likelihood ratio as for anyone chosen at random. Indeed, a criterion of random selection can lead to very small probabilities of guilt, for example if the population of a large city is taken as the reference group.

Other people might say, well, the defendant is either guilty or not guilty, so an equal chance of each alternative is a neutral starting point. For these people a probability of guilt of 0.5, and the same probability of innocence, is a fair starting point. Refusing to start with an inclination either way seems fair.

Currently, it is not routine for this to be mentioned in a trial. This may be because it is by no means clear that a starting point is necessary: why not just listen to the evidence and get on with it? The reason is that logical errors are likely to occur. A fact-finder will naturally ask, how much more consistent with guilt than with innocence is this evidence? This is the same as asking, what is the probability of the evidence existing on the assumption that the defendant is guilty, compared with the probability of that evidence existing on the assumption that the defendant is innocent. Having estimated that ratio, it would be tempting, but wrong, to conclude that the ratio expressed the defendant’s probability of guilt compared to probability of innocence. For example, if the issue to be determined was whether an unseen animal was a sheep, and the evidence was that it had four legs, the probability of getting the evidence that it had four legs if it was a sheep (P = 1) is not the same as the probability that it was a sheep if all that is known is that it was a four-legged animal. The error is called transposing the conditional.

Another reason for the priors not being mentioned at trial may be that there is no need to do so. Some evidence setting the scene, background evidence, is likely to have been given as part of the narrative. For example, if a crime was committed by a person in a building, video surveillance evidence may be that only 10 people were in the building around the relevant time, including the defendant. This supports priors of P'(G) / P'(NG) = 0.1 / 0.9. Another example is where it is conceded by the prosecutor that only one of two people could have committed the crime, the defendant being one. It would be intuitive to think that this gave equal priors of P(G) = P(NG) = 0.5. But the prior likelihood of each suspect being the offender may not be equal, and the question becomes to what extent should the fact-finder be given evidence of the unevenness of the respective prior likelihoods.

To get from the evidential likelihood ratio P(E|G) / P(E|NG) [which is read as: the probability of getting the evidence, given that the defendant is guilty, compared with the probability of getting the evidence, given that the defendant is innocent] to the ultimate issue ratio of P(G|E) / P(NG|E) – that is, to legitimately achieve the transposition – it is necessary to multiply the likelihood ratio for the relevant issue by the priors. The need to do this comes from mathematical logic, in a rule known as Bayes’ Rule or Bayes’ Theorem. A form of the rule useful for lawyers is the “odds form of Bayes’ Rule” described, for example, in Bernard Robertson, GA Vignaux and Charles EH Berger, Interpreting Evidence – Evaluating Forensic Science in the Courtroom (2nd ed, John Wiley and Sons Ltd, Chichester, 2016) at 189, [A.2.7]. The logic applies to all forms of conditional probability evidence, not just to scientific evidence. And anything, the probability of occurrence of which varies according to context, can be expressed in terms of conditional probability.

This ratio of priors is the starting point mentioned above, and the problem is, how should it be assessed? The risk is that individual jurors might choose different starting points and indeed may choose any position between the alternatives mentioned above. This is why sufficient evidence needs to be given to establish the prior probabilities.

People who think that the priors should be P’(G) = P’(NG) = 0.5 have the advantage of being able, without error of logic, to say that P(E|G) = P(G|E) and that P(E|NG) = P(NG|E). This is because, for them, the priors do not affect the calculation. Using Bayes’ formula reveals that to find the defendant guilty, a person who starts by understanding the priors to mean P’(G) = P’(NG) = 0.5 will only need the combined (that is, multiplied) likelihood ratios of the other evidence in the case to be about 50 to 1: meaning that the combined evidence is 50 times more likely to have been obtained if the defendant is guilty than if the defendant is innocent.

But a person who understands the priors to mean P’(G) = 0.02 and P’(NG) = 0.98, will, to find the defendant guilty, require the evidence to be about 2400 times more likely to have been obtained if the defendant is guilty than if the defendant is innocent. Leaving the assessment of the priors to individual jurors has obvious dangers.

In a civil case, for example an action for compensation for wrongful conviction, the ultimate issue must be proved to a probability of at least just over 0.5. Again, the level of proof required of the evidence depends on the priors. In civil cases it is especially tempting to think that priors of 0.5 each way is fair. To succeed in a claim for compensation the former defendant (now, plaintiff) would have to prove that the evidence in the criminal trial was slightly more likely to have been obtained if the defendant had been innocent than it was to have been obtained if the defendant had been guilty. But it still may be objected that the prior assumption of a probability of guilt of 0.5 is too high and that the probability attaching to a randomly chosen person should be used.

So a person who has been found not guilty, even on the assumption that the priors are 0.5 each way, may nevertheless fail to obtain compensation: this is because, although the evidence was less that 50 times more likely to have been found if the defendant was guilty than it was to have been found if the defendant was innocent, it may have still been more likely to have been found if the defendant was guilty than if the defendant was innocent.

The point is that to make presuppositions about the defendant’s guilt or innocence legitimate, those probabilities must be assessed from evidence given at trial.

It is appropriate to ask whether assessment of evidence outside a trial context should attract the same logic. For example, does the logic apply to assessing the sufficiency of evidence to meet a requirement of reasonable grounds to suspect that evidence will be found in a search? As may be illustrated by the case I discussed here on 31 July 2017, some judges might think it does, some that it doesn’t. Judicial explanations do not go far enough for us to be sure.

I should add that when mentioning “guilt” in the above discussion I am referring to single-issue cases (for example, who did it, or was it done intentionally?). Where several issues are at play in a case, guilt on each will need to be considered separately. That will avoid the swamping effect of a large likelihood of evidence being obtained on one issue (for example DNA evidence proving the defendant’s presence) overwhelming proof of another issue (such as the defendant’s state of mind).

Assessing reasonable grounds to suspect

Whether there were “reasonable grounds to suspect” the commission of an offence can be controversial. Recently our Court of Appeal has divided over whether there were reasonable grounds to suspect that the defendant had possession of an offensive weapon. The case is not yet publicly available, but suppression orders have lapsed. For people who have access to the databases the neutral citation is [2017] NZCA 108. When it is available it should be obtainable at (as number 108 in the list).

Reasonable grounds to suspect that a weapon will be found are required by s 27 of the Search and Surveillance Act 2012. Relevant matters were that it was 3 am when the defendant was questioned on a street and his response was “very cagey” as to where he had come from and why he was in the street and not wearing shoes although it was cold, his clothing (shorts and a camouflage jacket) was similar to that of a person who was believed to be involved in stealing from cars, he kept his hand in his jacket pocket and was behaving in an agitated manner (at [17]). These circumstances where held to have given the officer reasonable grounds to suspect that the defendant was in possession of an offensive weapon. Peters J (who delivered the Court’s judgment) recorded her dissent on this point. She did not consider that the circumstances relating to the initial dispatch to the scene suggested violence or a person with a weapon, and although the defendant was agitated nervousness is insufficient, and the defendant had simply kept his hand in his pocket. Further, he had identified himself, and there was nothing to suggest that he was going to use violence, particularly as four constables were present at the time of the search (at [26]).

The difference between the judges may be due to what assumption was be made at the beginning of the analysis. Should the defendant be assumed to have the probability of carrying a weapon that a randomly chosen person would have, or a randomly chosen person of the defendant’s age, and gender (to mention the two morally acceptable groupings), at that time of night? To avoid exaggerating individual facts which will be considered later in the analysis, the most neutral starting point should be chosen: the probability that a randomly chosen person has possession of a weapon.

However, another starting point sounds as if it is fair, but it will often lead to the opposite conclusion. This is that the defendant is just as likely to have a weapon as not to have a weapon. The even balancing here sounds neutral, until one asks, why should the defendant be assumed to have a probability of 0.5 of having a weapon? It may be that only 2 people out of every 100 have possession of weapons, so why not start with a probability for this defendant of 0.02?

Having chosen a starting point, the particular circumstances are examined. The judges may well have agreed on the probative value of each item and on the effect of taking them all into account together. Suppose that they agreed that the occurrence of these combined circumstances was 14 times more likely if the defendant had possession of an offensive weapon than if he did not. A judge who started with an assumption that the defendant was no more likely to have a weapon than would a randomly chosen person, would conclude that the ultimate probability that he had a weapon was around 0.3. This could not be reasonable grounds to suspect. But a judge who started with the assumption that the defendant was just as likely to have a weapon as not to have one, would conclude that the ultimate probability that he had one was over 0.9. This would certainly be equivalent to reasonable grounds to suspect possession of a weapon.

This analysis, which uses Bayes’ Theorem (something I didn’t mention so as not to put off many readers), shows how important the initial assumption is. A judge who started with the 0.5/0.5 assumption (giving Bayesian priors of 1) would think that was a fair starting point, but was it?

The judgment does not mention whether any offensive weapon was found in the defendant’s possession; other specified incriminating things were found, in respect of which he was charged.

The meaning of means: mental elements of drug importation in Australia

To find out what the law is you first look for relevant legislation. When deciding how to explain the law about the state of mind required for proof of unlawful importation into Australia of a border controlled drug, a judge will first look at the Criminal Code (C’th). Relevant sections are s 307.1 and the fault elements defined in ss 5.1 – 5.4.

The High Court of Australia in Smith v The Queen, The Queen v Afford [2017] HCA 19 (10 May 2017) (hereafter “Smith”) at [69] has given guidance as to how to logically apply this legislation to cases where the mental elements of unlawful importation of a narcotic are in issue.

These appeals reached the High Court because of difficulties around how the process of drawing inferences should be explained. Difficulties arose because of the need for intention as to one element but only recklessness as to another. Intention is necessary as to the bringing of a thing (whatever it may be) into Australia, and recklessness is sufficient as to whether it is a border controlled drug.

Inference drawing is a matter of proof. Proof of intention by inference can arise from circumstances which show that the defendant “was aware of the likelihood, in the sense that there was a significant or real chance, that his conduct involved [the prohibited] act and nevertheless persisted in that conduct”: Kural v The Queen (1987) 162 CLR 502, [1987] HCA 16 (and quoted in Smith at [7]). The statutory language changed after Kural, and now the concept of a significant or real chance calls to mind the phrase “a substantial risk” in the definition of recklessness (s 5.4).

The risk of confusing the old common law with the new statutory language no doubt lies behind the joint judgment’s comment in Smith at [68] that “looking to the future it might be preferable if directions given in cases like these were made to align more closely to the language of the Code, and in particular to the statutory definition of intent in s 5.2”.

In s 5.2(1), intention includes meaning to do something, here, to import the substance (at [6]). The Court’s guidance as to appropriate directions on the drawing of inferences include (at [69] para 8(ii)) that it is open to use a proven belief that there was a real or significant chance that the thing was done, to support an inference that it was meant to be done. This comes from the Kural exposition of the law, and needs to be read in the light of the Court’s fuller explanation. The point in Smith is that awareness of a real or significant chance means that “it is open to infer on the basis of all the facts and circumstances of the case that the accused intended to import the substance” (at [60]), and where “a person is aware of a real or significant chance of the presence of an extraneous substance in an object which the person brings into Australia, and does nothing by way of inspection or declaration to avoid the risk of its presence, the circumstances of the case strongly suggest that the person’s state of mind is, in truth, that he or she is prepared to proceed with bringing the object into Australia even if the substance is in the object; and thus that the person means and intends to import the substance” (at [59]).

This is perilously close to recklessness at common law, and one must wonder whether attempts to substitute for the clear language of a statute are necessarily helpful. Did the word “means” in s 5.2(1) really need to be explained in terms of a real and substantial risk?

Knowledge, in law, includes wilful blindness. This is the state of mind of a person who ignores a suspicion because of a determination to remain ignorant of the truth. That person is deemed to know the truth. See R v Briscoe 2010 SCC 13, [2010] 1 SCR 411, and R v Martin [2007] NZCA 386 at [11] where consistency with R v Kural [1986] VR 673 at 676-678 is noted. So, acting with that knowledge is meaning to do that thing, and is intending to do it. This is different from recklessness, where a person simply fails to take the measures that a reasonable person would have taken to investigate whether the suspicion is true.

Interesting decisions pending

As you know by now, much of law involves waiting. Waiting for decisions of appellate courts gives law much of its suspense. Perhaps. Here are some interesting points awaiting determination:

Grounds for search

When the adequacy of grounds for a search are assessed, should illegally or improperly obtained information be disregarded? An appeal from [suppressed] [2015] NZCA 628 is on the way.  [Update: Oops, this escaped my attention; it was decided on 29 March that information that has previously been ruled inadmissible may usually (except in extraordinary circumstances involving torture or violence) be used in an application for a warrant, but when admissibility of evidence consequently discovered is determined the illegality or impropriety will be relevant to the balancing exercise: [2017] NZSC 42. I expect the effect of this will be to reduce the exclusionary effect of s 30 of the Evidence Act 2006 by permitting the admission of improperly obtained evidence of less serious offences than previously.]

Mental elements of unlawful drug possession and related offences

Does the mental element that makes possession of a drug unlawful include recklessness? Related to this, is there a good-faith defence, and if so, when? I’m not sure if there are suppression orders still in effect in this one, but let’s pretend there are: see [suppressed?] [2016] NZSC 87 (leave granted). [Update: on 19 June 2017 the Supreme Court decided that recklessness is sufficient mens rea for drug offences if no more specific state of mind is specified in legislation. There is therefore no need for a separate good-faith defence. Suppression of some details continues so I just mention the citation: [2017] NZSC 89.]

Privacy balancing

When, if ever, is a defendant’s right to privacy diminished by another person’s privacy right that has been breached by the defendant? If breach of another person’s privacy does reduce the defendant’s own privacy right for the purposes of the admissibility balancing exercise, would it be double-counting to also take the breach of the other person’s privacy as increasing the public interest in admitting the evidence? More abstractly, can policy justify compromising the logic of the balancing exercise, and if so, when? See [name suppressed] (CA597/2016) v R [2017] NZCA 118, granting leave for a second pre-trial appeal. [Update: On 17 November 2017 the Court released its judgment in this appeal, [2017] NZCA 522 (publication suppression orders still in force), holding that breach by the defendant of a third person’s privacy is relevant to the seriousness of the offending and weighs in favour of admission of the evidence, and is separate from and independent of the seriousness of the breach of the defendant’s privacy right, which weighs in favour of exclusion of the improperly obtained evidence. The Court cited favourably dicta in R v Patrick 2009 SCC 17, [2009] 1 SCR 579 at [32] per Binnie J for the majority.]

Is an electronic file an object?

The “Dotcom” case continues its slow climb up the judicial hierarchy, but it seems to me that the central point is easy to state (and should be easy to decide): is an electronic file an object in which there can be a copyright? An appeal, or two appeals, from Ortmann v United States of America [2017] NZHC 189 (see [169]-[192]) could settle that.

The Arnold Solution

I ask, just for fun, whether you have read Thurman Arnold’s “The Role of Substantive Law and Procedure in the Legal Process”. It is available courtesy of the Yale Law School’s Faculty Scholarship Series, here, and will also be found in 45 Harvard Law Review 617 (February, 1932). Yes, 1932.

He uses “procedure” in a special sense, rather than its classification as found in the law school curriculum (p 647, fn 44). Also used in a special sense is “substantive law” which is the body of legal precedent that has been established and which has been accorded reverence because of its attributes and those recognised in the legal system, and by society, attaching to courts. Substantive law concerns principles, whereas procedure is entirely practical. Procedure is not tradition-bound but changes in the light of practical requirements. Whereas substantive law may be restated, procedure can be reformed. The difference is only in attitude, “any doctrine may be treated as procedure and the problem discussed, or as substantive law and the principle stated” (p 643).

Given these special definitions of substantive law and procedure it is plain that Arnold is not talking about what we would call substantive law and procedure. So, what is he saying?

His fear is that the multiplication of precedents through increased reporting of cases will reduce the law to confusion and chaos. The way to avoid this, he says, is to reduce access to appeals. The English did this, he further says, in criminal law by requiring that a miscarriage of justice had to be “substantial” before an appeal against conviction would be allowed. This was a barrier which discouraged appeals and minimised disruption to the established body of precedent. (p 638)

“It is this ability of the English to keep an ideal from too close contact with reality which explains the prestige which they are able to throw around their institutions.” (p 640)

He quotes, at p 639 fn 29, the then hot-off-the-press Goodhart, Essays in Jurisprudence and the Common Law (1931) at 57:

“Perhaps the reason why the English Lawyer is not dissatisfied with the present system is that the ‘myriad’ precedents do not exist. The English cases to 1865 are reprinted in the English Reports in about 175 volumes. The semi-official Law Reports from 1865 to the present date occupy about 450 volumes. Thus 625 volumes make up a complete working library.”

Wonderful times indeed, not that I personally remember them. But how different is it today?

The point is not the number of volumes in which the law can be printed, but the ease with which the law can be ascertained. It hardly matters how many millions of precedents there are, if the relevant ones can be obtained from an electronic database almost instantly. Present problems are around applying acquired legal skills to honing down electronic search results to bring into focus the cases that are truly relevant, and keeping those to a minimum. A concentration on cases that have been cited and discussed in recent decisions should assist this focusing process. So instead of having 625 volumes on the shelves, a practitioner need only have a few leading textbooks and a subscription to an appropriate electronic database.

But Arnold, if he were here today, might still be concerned about what is happening, behind the electronics, to the law itself. Is it becoming uncertain because of confusion arising from what is, in effect, the use of legal principles as if they were rules. Multiplication of exceptions and additions of refinements could be moving the fundamentals in a way which makes them less venerable and worthy of the reverence that has, he would say, attached to the law and the courts. Would it be practical to counter this by restricting arguments about the application of precedent to trial courts, and only allow cases that require discussion of principles to go to the appeal courts?

This points to the real question, whether there is something that needs to be countered. Has the digital revolution saved the law from the Arnold solution?

Proving propensity

Propensity evidence is evidence about the defendant’s conduct, not directly connected to the presently alleged offending, but which shows a propensity to act in a way that is relevant to an issue now before the court. To what, if any, standard must propensity be proved before it can be used in the process of determining the facts on the present allegation?

The United Kingdom Supreme Court has held that propensity must be proved beyond reasonable doubt before it can be taken into account in fact-finding: R v Mitchell (Northern Ireland) [2016] UKSC 55 (19 October 2016).

The Court noted that the common law had not settled this question, and legislation only covered admissibility, not standard of proof.

New Zealand common law has taken the position, almost as a mere assumption, that no particular standard of proof of propensity is required, but that instead admissible evidence of propensity is just circumstantial evidence that can be considered with all the other evidence in determining guilt on the present charge. For example, see R v Guy (1996) 13 CRNZ 589 (CA). And if the defendant had been previously charged with offending that would be evidence of a relevant propensity, but had been acquitted, evidence of the facts supporting that earlier allegation can, notwithstanding the acquittal, be given to prove the propensity: R v Degnan [2001] 1 NZLR 280, (2000) 18 CRNZ 319 (CA).

Is there necessarily an inconsistency here with Mitchell? That case only requires the propensity, not the evidence of it, to be proved beyond reasonable doubt. Its effect is that the method for determining facts if propensity evidence is relied on is to consider all the admissible evidence of propensity, to assess it and to decide whether propensity is proved beyond reasonable doubt. If it is, then it may be taken into account with the evidence of the present allegation. If it is not proved to that standard it must be ignored. It is not mixed with the other evidence in the case when the fact-finder is deciding whether there is a propensity.

This is inconsistent with the New Zealand approach. See for example R v Holtz [2003] 1 NZLR 667, (2002) 20 CRNZ 14 (CA), discussed here on 14 October 2004, where no standard of proof is required except for an ultimate conclusion of guilt. It is sufficient (at [39]) that the fact-finder “conclude” or be “satisfied” that the evidence of propensity establishes the relevant propensity. There the Court “rejected a general requirement that pattern or the like must be found beyond reasonable doubt before similar fact evidence may be used”.

The Mitchell rule requires the fact-finder to ignore evidence that is in reality highly probative. The judicial consideration of a variety of solutions to this problem in HML v The Queen [2008] HCA 16 (discussed here on 26 April 2008) was not mentioned in Mitchell. In Mohammed v R [2011] NZSC 52, [2011] 3 NZLR 145, (2011) 25 CRNZ 223 (discussed here) the focus was on other aspects of how juries should be directed on propensity evidence, so this point may still be open.