Accounting for guilty pleas – justice, not economics

Whereas South Australia v Totani (last note) illustrated the error of a legislature in depriving a court of its judicial function, Hessell v R [2010] NZSC 135 illustrates a departure by a court (here, the lower appellate court) from its judicial function.

This is only hinted at obliquely. The Court was highlighting the inappropriateness of a formulaic approach to the level of sentence discount to be awarded for entry of a plea of guilty. The Court of Appeal in this case had issued a guideline judgment on discounts for guilty pleas, setting out a sliding scale according to the stage of the proceedings at which the plea was entered. The Supreme Court overruled that:

"[67] The law reform agencies in the United Kingdom and New Zealand saw valid reasons to move to a more prescriptive and structured approach to giving credit for guilty pleas in sentencing. The Court of Appeal was persuaded by their reasoning. But in giving effect to their proposals, the Court of Appeal has underestimated the complexity of the issue including the potential of the changes to impact on the protected rights of persons charged with criminal offending. It is also inappropriate for a court to make changes in sentencing policy that would restrict the capacity of judges to determine sentences that are considered to fit all the circumstances of the case. Where the development of sentencing policy is motivated by a utilitarian calculus it may not be appropriate for judicial decision. Judges should show restraint in moving beyond the area mandated by existing legislation when exercising their sentencing powers. The ultimate difficulty we have with the Court of Appeal's approach is that it is not mandated by the Sentencing Act." [emphasis added]

The Supreme Court's approach recognises the need to avoid coerced guilty pleas, and to protect the defendant's right to dispute the facts and to challenge the admissibility of evidence.

Sentencing involves the consideration of a range of circumstances, one of which may be a guilty plea, and the significance of such a plea has to be assessed in all the relevant circumstances of the case. However, the Court added that discounts for guilty pleas should not exceed 25%, as remorse is a separate consideration for which more credit may be due.

The Australian approach (R v Wong [2001] HCA 64, (2001) 207 CLR 584 at [76] per Gaudron, Gummow and Hayne JJ; R v Markarian [2005] HCA 25, (2005) 228 CLR 357 at [37] per Gleeson CJ, Gummow, Hayne and Callinan JJ) was preferred to that in the United Kingdom, although New Zealand uses more of an "instinctive synthesis" of gravity and culpability than does Australia: Hessell at 55.

Fundamentally, the Court of Appeal had addressed the question from a point of view that was distorted by non-judicial concern with administrative efficiency.

When laws go crazy

People interested in whether a legislature may require a court to act unjustly may get some pointers from French CJ's judgment in South Australia v Totani [2010] HCA 39 (11 November 2010).

This case was decided in the context of Australia's constitutional arrangements, but some fundamentals of interest to everyone are evident.

French CJ began by referring to the assumption of judicial independence which underlies the constitution [1] and which has its origin in English law [59], where fairness and impartiality were recognised as characteristics of proceedings in courts of justice [60]. While the characteristics of a court cannot be defined in a single all-embracing statement, an essential is the conduct of an adversarial trial by an independent and impartial tribunal [62]:

"At the heart of judicial independence, although not exhaustive of the concept, is decisional independence from influences external to proceedings in the court, including, but not limited to, the influence of the executive government and its authorities [footnote: As to the multiple location of judicial decisional independence in separation-of-powers protections providing for "judicial independence" and within the rubric of "due process" and "the rule of law", see Gerangelos, The Separation of Powers and Legislative Interference in Judicial Process, (2009) at 8]. Decisional independence is a necessary condition of impartiality. Procedural fairness effected by impartiality and the natural justice hearing rule lies at the heart of the judicial process [footnote: For a recent discussion of the natural justice hearing rule in this context, see International Finance Trust Co Ltd [2009] HCA 49; (2009) 240 CLR 319 at 379-384 [139]- [150] per Heydon J.]. The open-court principle, which provides, among other things, a visible assurance of independence and impartiality, is also an "essential aspect" of the characteristics of all courts, including the courts of the States [footnote: Russell v Russell [1976] HCA 23; (1976) 134 CLR 495 at 520 per Gibbs J; see also at 505 per Barwick CJ, 532 per Stephen J; [1976] HCA 23]."

Important for this case, but also of potential general application, is the idea that a legal system cannot require a court to act in a way which impairs its "institutional integrity". In the context of Totani, this idea appears as [69(3)]:

"The institutional integrity of a court requires both the reality and appearance of independence and impartiality [Footnote: Forge [2006] HCA 44; (2006) 228 CLR 45 at 77 [66] per Gummow, Hayne and Crennan JJ, citing Ebner v Official Trustee in Bankruptcy [2000] HCA 63; (2000) 205 CLR 337 at 345 [7]- [8] per Gleeson CJ, McHugh, Gummow and Hayne JJ]."

And the fundamental nature of that requirement - the reality and the appearance of independence and impartiality - is historical, pre-dating Australia's federation [72]:

"...Forms of external control of courts "appropriate to the exercise of authority by public officials and administrators" are inconsistent with that requirement [Footnote: Gypsy Jokers Motorcycle Club Inc v Commissioner of Police [2008] HCA 4; (2008) 234 CLR 532 at 553 [10] per Gummow, Hayne, Heydon and Kiefel JJ ]. The requirement is not a judicially generated imposition. It derives from historically based assumptions about courts which were extant at the time of Federation."

This form of argument is potentially a powerful weapon against those who would support the idea that a sovereign legislature may enact any law it wishes. I have a written a brief note on this sort of thing in "Criminal Equity" [2000] New Zealand Law Journal 427. By "criminal equity" I mean the pursuit of fairness in the criminal context by looking beyond the black-letter law. Since then, we have enacted a potential cause of unfairness in s 21 of the Evidence Act 2006[NZ] which is absolute in its terms. It is wide enough to prevent admission of the exculpatory parts of a defendant's statement to the police unless he gives evidence at his trial. In cases where this would operate unfairly, the court has to, in effect, disregard s 21, but, since the court does not have the power to rule the legislation unconstitutional, this is done under the guise of recognising an implicit power to require the prosecution to lead the exculpatory statement to prevent unfairness. In a case that seems to be currently subject to a suppression order, [2009] NZCA 607, (2009) 24 CRNZ 527, the Court of Appeal has said, at [19]:

" ... such a power must be implicit in s 25 of the New Zealand Bill of Rights Act 1990. In the event of an unfair decision by a prosecutor not to lead evidence as to what an appellant said at a police interview, it would thus be open to the Court to require that evidence to be led. As to this, see Illingworth and Mathias “The Admissibility of Hearsay Statements and Opinion Evidence” in Young and Chambers Evidence Act 2006 (NZLS Intensive June 2007) at 50 – 51."

Essentially this is using the inherent power to prevent an abuse of process to qualify the statutory language in the interests of trial fairness. The jurisdiction to prevent an abuse of process is inherent in the function of the court.

Fair multiplicity

A routine point of criminal law was the reason for the unopposed allowing of the appeal in Mason v R [2010] NZSC 129 (3 November 2010): s 329(6) of the Crimes Act 1961 provides that "Every count shall in general apply only to a single transaction." Here, the transaction covered two assaults, and these should have been charged separately to avoid unfairness: the accused may have had a defence to one assault, and on sentencing it would be necessary to know what had been proved beyond reasonable doubt especially because the assaults varied in seriousness.

The conviction was quashed and the Crown did not seek a retrial.

This rather elementary point had been overlooked in the Court of Appeal, where the appellant had represented himself and the Court had misunderstood his argument as applying only to the determination of facts for sentencing.

Mr Mason will no doubt be pleased he did not have to go to the trouble and expense of trying to appeal to the Privy Council. This was a minor case, alleging punching in the face and ear-pulling, committed against one of the accused's sons. It was only interesting because of the huge attention that the use of force in domestic discipline has recently received, and this was regarded as a test case for new legislation, s 59 Crimes Act 1961.

There are occasions where a count can allege offending over an extended period, and there may be many alleged incidents which a complainant cannot be specific about. In those cases (often, but not necessarily, alleging sexual misconduct) the jury must, before it can find guilt, agree on at least one incidence of the alleged offence.

A leading authority is R v Accused (CA160/92) [1993] 1 NZLR 385; (1992) 10 CRNZ 152 (CA), where the judgment of the Court of Appeal was delivered by Cooke P (later, Lord Cooke of Thorndon). On the requirement of trial fairness, his Honour said

"The basic ingredients of a fair trial remain. There are limits to custodial interrogation and in some circumstances Bill of Rights protections; the accused is entitled to know the substance of that with which he is charged; he has statutory and common law rights regarding the disclosure of certain information; he has detailed notice before the trial of the evidence to be called by the prosecution; he has the right at the trial of cross-examining the Crown witnesses, subject to some reasonable restraints; he has the right to give evidence himself, so that the jury may compare his evidence with that of the complainant or his other accusers; and he has the benefit of the doubt, invariably underlined by trial Judges in emphatic directions that the prosecution must establish its case beyond reasonable doubt. In the event of a conviction the accused has the right of appeal on grounds including the basic one, miscarriage of justice. There is the safety net for exceptional cases of the Royal prerogative and s 406 Crimes Act: see Burt v Governor-General unreported, 16 July 1992, CA175/88.

"On the general question of the fairness of criminal trials in New Zealand it is not to be overlooked that other developments, some of them with no particular bearing on sexual charges, have also moved the balance towards the prosecution. These include statutory provisions for electronic surveillance; DNA testing; a more liberal judicial attitude to "similar fact" evidence and hearsay evidence. But they have been accompanied, at least since Police v Hall [1976] 2 NZLR 678  and R v Hartley [1978] 2 NZLR 199, with affirmation of the Court's inherent jurisdiction to prevent unfair trials; and that jurisdiction would be available if truly needed in a case in the present field.

"It is possible to imagine a case in which allegations of sexual misconduct are so vague or relate to a time so long ago, without justification for the delay, that it would be unfair to place an accused on trial upon them. Then the possibility of exercising the protective inherent jurisdiction would fall for consideration in all the circumstances of the particular case."

This comes down to the avoidance of vagueness and the avoidance of prejudicial or unconscionable delay. Logical difficulties may persist, as mentioned in the discussion of the use of specimen or sample counts in Tyack v. The State (Mauritius) [2006] UKPC 18 (29 March 2006) at 18-21. The problem is one of framing legislation that permits inclusion of more than one occurrence of an offence in one count, while still complying with the right to a fair trial. The New Zealand provision, s 329(6) above, is not absolute, but applies "in general" to a single "transaction". In Mason the Supreme Court said of this:

" [9] ... The qualification "in general" and the relatively indefinite word "transaction", which can encompass both a single event or a course of conduct, recognise the difficulty of application of any precise rule to the charging of the many different fact situations in which acts of offending may occur. They indicate the need for some flexibility. The essential requirement emerging from case law is that, if particular acts of alleged offending can sensibly be charged separately without undesirably lengthening the indictment (overcharging), then that should be done. It is necessary that distinctly identifiable acts of alleged offending be the subject of separate charges where the accused may be prejudiced either at trial or on sentencing if they are combined in a single count. On the one hand, the use of a multiplicity of counts is to be avoided where fewer would suffice for the interests of justice. On the other, overly complex counts may prejudice the defence or make it difficult to frame fair and accurate directions to the jury. If necessary trial Judges should intervene if either problem arises.

"[10] We repeat what Anderson J said for this Court in R v Qiu [[2007] NZSC 51, [2008] 1 NZLR 1 at [8] ].The Court endorsed the practice of not charging as separate offences a continuing course of conduct which it would be artificial to characterise as separate offences. But the Court said that it was another thing to charge as a single count repetitive acts which can be distinguished from each other in a meaningful way, even if they relate to more than one act of a certain class or character. The Court added something which the present case vividly illustrates:

'Separate counts facilitate fairness in the conduct of the trial by focusing attention on matters of fact and law which can and need to be distinguished for the purposes of different counts. In the event of conviction, they assist the sentencing Judge by indicating the extent of culpability.'"

Some delicate calculations may need to be made, as appears to have been the position in Mason, where experienced defence counsel had not sought severance of the count. Presumably this was because the chances of a successful defence to the lesser allegation were thought to be low, and that even if successful, splitting off the lesser allegation would merely highlight the more serious one and would prevent a sentencing submission that the facts should be assessed as less serious than they could have been. Fairness to the defence is not always easy for the defence to accept, as was seen earlier in these notes in relation to leaving alternative counts to the jury: "Fairer than you may want" .

Good character direction

An addition to our collection of cases illustrating when absence of a good character direction requires the quashing of a conviction: Campbell v R [2010] UKPC 26 (3 November 2010).

Here the omission of the direction was not the result of a tactical decision by the defence, and the case involved a contest between an eyewitness and the accused who gave evidence. In such cases the direction would be "of greatest potential significance" (para 45).

The Board also summarised the requirements for an eyewitness identification direction (para 28), and began with an extended discussion of when the Board can grant special leave to appeal to it where the lower court has refused leave (para 5-25).

W(h)ither Weiss?

Usually only one side in a criminal case appeals, but in R v Nguyen [2010] HCA 38 (3 November 2010) the Crown appealed against the Court of Appeal of the Supreme Court of Victoria's quashing of convictions for murder and attempted murder and its entry of acquittals, and the accused (DQN) appealed on the basis of an alleged misdirection by the trial judge by way of failure to leave to the jury the alternative of manslaughter on each count. DQN's appeal point had been raised in the Court of Appeal but was not addressed in its judgment.

The High Court therefore had to consider, on the Crown's appeal, whether the Court of Appeal had been correct in holding that the verdicts had been unreasonable, and on DQN's appeal, whether there had been an error of law.

Both these appeals had to be decided: it would have been insufficient to simply dismiss the Crown's appeal because there had been a substantial miscarriage of justice, because that would leave standing the Court of Appeal's entry of acquittal.

In the result, the Crown was entitled to a retrial because the verdicts were not unreasonable and the Court of Appeal should not have allowed DQN's appeal on that ground. There had to be a retrial because DQN's appeal also had to be allowed: there had been a substantial miscarriage of justice at trial.

Do these two grounds of appeal – reasonableness of verdict, and error of law giving rise to a miscarriage of justice – require different approaches by the appellate court? Both are subject to the proviso that the appeal may be dismissed if no substantial miscarriage of justice had actually occurred.

What is interesting about the High Court's judgment is its absence of reference to Weiss v R (2005) 224 CLR 300. Weiss requires the appellate court, upon finding that there was an error at trial giving rise to a miscarriage of justice, to determine whether the miscarriage was "substantial" by examining the whole of the record to assess whether the prosecution case was proved beyond reasonable doubt. Should you wish, you may locate my earlier comments on this by searching this site on the word Weiss.

In Nguyen the Court applied M v R [1994] HCA 63, (1994)181 CLR 487. This involves asking "was it open to the jury" to convict? It differs from the Weiss question, "is the appellate court satisfied of guilt"?

Plainly, the High Court could not apply Weiss because that would involve saying that it was satisfied of guilt, and also that there had been a substantial miscarriage of justice arising from failure to leave the jury with the alternative of manslaughter. The implications of this appeal highlight how inappropriate the Weiss approach can be.

Classic probability conundrums

There are many examples online of probability conundrums. I have mentioned some in my draft paper on propensity evidence, linked on this page. I mention two of them here.

The first problem is, if you are told that a stranger to you has two children, at least one of whom is a boy, what is the probability that the other is also a boy?

Note that neither child has been singled out, so this is a problem about the probability of having two boys. Given that one child will have been born before the other (even if a twin), the two children can have arrived as BB, BG, GB. The other combination, GG does not count in this example. So, one out of three eligible combinations gives two boys, and the probability of that occurring is 0.33.

If one child had been singled out, the problem would have been about the gender of one child (the other one). You might have been able to see one child, and were asked about the other. For one child, the probability of it being a boy is 0.50.

This problem illustrates how important it is to ascertain exactly what the issue is. The seemingly endless argument about this problem in the discussion to the above NY Times article exemplifies this.

Some people wonder why the combinations BG and GB are counted separately. They would say that the relevant combinations are just two: BB and (B and G). The error here is in thinking (B and G) will occur just as frequently as BB. This overlooks the way in which the data can arise. (B and G) will occur in two ways (namely, BG and GB) whereas BB will occur in only one way.

So the two lessons from this problem are: ascertain the issue, and examine how the data arises.

The other problem is known most commonly as the Monty Hall problem, after a game show host. The task is to pick which of three doors, A, B and C, will when opened reveal a prize. You pick one door, say A. The host, who knows where the prize is, then tells you it is not behind door C. Should you change your guess to door B?

When you choose door A, you divide the doors into two groups or classes: the chosen and the not-chosen. The probability of the prize being behind door A is 0.33. The probability of it being in the not-chosen class is 0.67. Once the host eliminates one member of the not-chosen class, the class probability for that class attaches to the only remaining member, door B. You should change your guess.

Some people object that each door always has the same probability of concealing the prize, and that there is no reason to change your guess from A. This ignores the new information the host gives you. Changing the probability distribution among members of one class does not affect the probability distribution among member(s) of another class. The constant probabilities are wrongly linked to the individual doors, rather than to the classes.

The lessons from this example are: use all the relevant information, and recognize when the issue is about members of one class as distinct from members of another class.

Another look at the right to legal advice

The relationship between the right to legal advice and the right to a fair hearing, discussed here in commentary on R v Sinclair, 15 October 2010, was again a central theme in yesterday's United Kingdom Supreme Court decision, Cadder v HM Advocate [2010] UKSC 43. In this case the law of Scotland was brought into line with the law in other jurisdictions that apply the European Convention on Human Rights.

I suggested that Sinclair will have to be applied in a way that preserves the defendant's absolute right to a fair hearing. This too is a requirement of Cadder. All members of the Court agreed with the two leading judgments (although technically Lord Mance agreed with Lord Hope but through him also agreed with Lord Rodger). Lord Rodger put the relationship between the non-absolute right to legal assistance and the absolute right to a fair trial this way (95):

"First, as the European Court recognises, [in Salduz v Turkey] 49 EHRR 421, 437, para 55, since the right to legal assistance at the stage when a suspect is to be questioned is an implied right, it is not absolute and must be subject to exceptions when, in the particular circumstances, there are compelling reasons to restrict it. It is not suggested that there would have been any such reasons in this case. But the circumstances in which section 15 of the 1995 Act envisages delaying intimation to a solicitor (the interest of the investigation or the prevention of crime or the apprehension of offenders) could perhaps constitute compelling reasons to restrict the right of access in an appropriate case. It has to be remembered, however, that even a justified restriction may deprive an accused of a fair hearing and so lead to a violation of article 6: 49 EHRR 421, 436, para 52."

Key concepts are the "compelling reasons" needed before the right to legal assistance can be restricted, and the nature of the "fair hearing". Neither of those called for detailed consideration in Cadder.

I doubt that in practice the correct application of Sinclair will produce different outcomes in Canadian courts from those in Scottish courts under Cadder.

Lord Rodger at 100-103 also dealt with the argument that changing the law of Scotland now would create a need to revise all the decisions that had applied the earlier law, by applying dicta in A v The Governor of Arbour Hill Prison [2006] 4 IR 88, per Murray CJ at paras 36-38.

Lord Hope referred to Gafgen v Germany (a case discussed here on 3 July 2008, 3 December 2008, and 25 June 2010, and also in Part 3 of the overview of these notes posted on 14 January 2010). He held at 48 that Gafgen turned on it's facts and was not a limitation of Salduz.

With there now being less wriggle-room concerning rights compliance, attention will focus on whether waiver of the right to legal advice had been constituted by the defendant's continuing cooperation with police questioning.

Provoking nostalgia

I recall that some of the better law students used to laugh at judges' efforts to elucidate the acts reus of attempts, especially impossible attempts, and also at their efforts to explain what provocation is. The latter has remained problematic, as can be seen from today's High Court of Australia decision in Pollock v R [2010] HCA 35. The case illustrates how even Bench Book directions derived from appellate judgments can be held by a higher court to be wrong.

In New Zealand we have repealed the statutory defence of provocation, as it is no longer thought to be necessary since the penalty for murder can in exceptional cases be less than life imprisonment. I am sure that, once the question of provocation is explored in sentencing hearings, the old difficulties will be revived.

Now that the questions concerning liability for impossible attempts have been solved, and provocation has diminished in importance, law students will be starved for intellectual stimulation in criminal law. Is there really anything worth puzzling over as far as the ingredients of offences and defences are concerned? Surely the focus of interest has shifted to admissibility issues, especially those involving rights.

So there is some nostalgia in reading Pollock - those old familiar authorities, those old familiar errors.

The right to legal advice

The requirement that a confession must be voluntary has several components. One is the right to silence, and waiver of this right must be informed and freely exercised (another requirement of voluntariness). The need for "informed" waiver of the right to silence is the reason that a caution has to be administered before a suspect is interviewed. The caution also contains information about the right to legal advice. This right to legal advice protects the "informed waiver" component of the right to silence, but it also extends to protect the ongoing requirement of voluntariness that continues throughout an interview. It should ensure that the suspect knows that he can exercise the right to silence at any time during questioning. The suspect is entitled to advice which will inform him of the significance of the questioning that will occur: its importance for potential proof of criminal liability. That means that the legal adviser needs to know what offences might be charged and the way in which liability for them might arise from the suspect's answers if he is to be questioned.

When one asks what the right to legal advice entails, this context of the right in relation to voluntariness of a potential confession needs to be remembered. Does this context make the operation of the right to legal advice in any particular case a matter for balancing against other interests, such as the public interest in the bringing of offenders to justice? Or is the right to legal advice an absolute right because of its being a component of the voluntariness of a confession?

This latter position, absoluteness, was taken by LeBel, Fish and Abella JJ in R v Sinclair [2010] SCC 35 (8 October 2010) and again in a companion case decided the same day, R v McCrimmon [2010] SCC 36. They said that what needs to be justified is a limitation on the right to legal advice, not the exercise of the right (McCrimmon at 39). Their concern with the power imbalance inherent in a police interview led them to repeat the dissent they had issued in Sinclair.

I should say, parenthetically, that it was illegal for those judges to repeat the dissent: since the matter was decided by the majority in Sinclair, they were obliged to follow the law and apply Sinclair. They could have still in McCrimmon reached the same conclusion as they did, by turning attention to the requirement of voluntariness. Unfortunately, the splitting of issues on appeal has led to the right to legal advice being considered in detail but without its important context of voluntariness. There was necessarily some mention of voluntariness, but this was more by way of aside (see, for example, the majority in Sinclair at 62).

The majority in Sinclair (McLachiln CJ and Charron J, with Deschamps, Rothstein and Cromwell JJ concurring) held that the right to legal advice involves an initial informing and a reasonable opportunity to exercise the right. It does not include a right to have counsel present throughout the interview. There may, during the course of an interview, be a need for a further opportunity for legal advice, but this arises only where it objectively appears that the initial advice could have been inadequate or where a new issue makes an opportunity for advice appropriate. It is not enough that the suspect merely wishes to interrupt an interview, as the suspect can exercise the right to silence. Fundamental to the majority's approach is the view that ascertaining the contours of the right to silence requires consideration of societal interests in the investigation and solving of crimes (Sinclair at 58, 63).

One would have to think very carefully before venturing to disagree with Charron J on a point of the law of evidence. Whether or not one agrees with the majority reasoning should depend on whether one accepts that qualifying the right to silence, by qualifying the right to legal advice, risks jeopardising the absolute quality of the requirement that a confession is made voluntarily. The majority's reasoning seems to be that qualifying those subsidiary rights may be acceptable as long as the voluntariness of any confession remains absolute. That would be analogous to reasoning that has been used in relation to rights associated with the accused's absolute right to a fair trial (see, for example, R(Ullah) v Special Adjudicator noted here, and with reference to judicial difficulties, 3 September 2004).

The Sinclair majority's reasoning is anchored to an appreciation of the "broad sense" of voluntariness required for confessions (Sinclair at 62), but unfortunately these cases have no detailed discussion of voluntariness. The majority makes great claims for the role of the voluntariness requirement (Sinclair at 64: "If anything, our reasons broaden the protection available to suspects, and narrow the ambit of police questioning"), and there will be many who read that sceptically. A consequence of finding no breach of the right to legal advice if there was no impact on the voluntariness of a confession is that there would be no need for the balancing exercise to determine the admissibility of the confession (in Canada, the Grant balancing) in such cases. Of course, if there was an impact on voluntariness, exclusion would be automatic. But cases of lesser police impropriety would be immune from judicial criticism in the form of exclusion. A very "broad" sense of voluntariness would be needed to address those.

Also decided the same day was R v Willier [2010] SCC 37, in which the Court unanimously held that on the facts there was no breach of the right to legal advice. Each of the approaches, so different in philosophy, can still lead to agreement on particular facts.

There is a brief but interesting discussion of the relevance of foreign law (here Miranda) to the question of the meaning of the right to legal advice, in Sinclair at 38-42.

See also my discussion of R v Singh, 2 November 2007. And for the position in Europe, see Salduz v Turkey [2008] ECHR 1542 at para 50-55.

Interpreting positive drug tests in cyclists

I am not a great follower of the sport of cycling. Apparently it is bad for the health of male genitals, and I can see why. But recently a successful cyclist, Alberto Contador, has tested positive for a minute trace of a substance that is banned. His explanation is that it must have been in meat he innocently ate. Farmers do use that drug to improve the muscle mass of their cattle. It seems to be thought that the controversy will be resolved by a second test of Mr Contador's body fluid samples.

 Nonsense. The occurrence of the drug in people who eat meat from the same source as Mr Contador's meal must be examined. The probability of getting Mr Contador's test result, on the assumption that he is guilty of deliberately taking the drug, must be compared with the probability of getting his test result on the assumption that he is innocent. This latter is the proportion of people who have a similar test result who got that result innocently from eating.

Scientific reasoning is comparable to legal reasoning. In science the method of investigation involves attempting to disprove a null hypothesis. For example, if the null hypothesis was “this drug test result could not have been caused by food”, scientific inquiry would involve looking for an instance where the relevant sort of food consumption caused the same test result. Falsification of the null hypothesis was the criterion for scientific advance recognised in the scientific community and famously described by Karl Popper.

In legal reasoning applicable to criminal trials, the prosecution’s hypothesis is the null hypothesis (“this drug test result could not have been caused by food”). But it is not for the defence to disprove the null hypothesis. Of course, the defence could seek to do so, and would win if it did produce evidence that the null hypothesis was false. But generally it is for the prosecution to prove that there is nothing to falsify the null hypothesis. “Progress” in this legal context occurs where there can be no disproof of the null hypothesis, whereas in science progress is disproof of the null hypothesis. Obviously, whereas disproof of the null hypothesis occurs by a specific event, the prosecution’s task of showing there is no disproof of its hypothesis can only be a matter of likelihood.

A disadvantage of the scientific method is that disproof may be a long time coming, and this will slow down progress. Disproof has, in recent times, been complemented by another technique: asking what is the most likely hypothesis behind given observations. Given the drug test result, what is the most likely explanation? Law is similar: given the evidence, is the defendant’s guilt the most likely (to the necessary high standard) explanation? On this approach, conditional probabilities come into play. Hypotheses are compared as explanations for the observations or for the evidence. Bayes’ Theorem is a means of assessing the likelihood of an hypothesis as an explanation for an observed fact.

Mistakes in logic can be identified using Bayes’ Theorem, and it is not necessary for this that actual probabilities are known. A common error in logic is to say that the probability of A, given B, is the same as the probability of B, given A. Using the example of a (any) cyclist, the error would be in saying that the probability of this test result, given that the drug was taken deliberately, is the same as the probability that the drug was taken deliberately, given this test result. Another error of logic is to suppose that the likelihood of the cyclist having cheated can be derived directly from the likelihood of the drug having been in his food. This error is that of ignoring the other probabilities of the cyclist having cheated, taking into account all the relevant facts. A Bayesian approach avoids both these sorts of errors.