The Law Commission’s 2013 Review
Tuesday, October 08, 2019
Probative value and prejudicial effect: when weighing is not balancing
Weighing probative value against unfairly prejudicial effect
Section 8 of the Evidence Act 2006 sets out a generally applicable exclusionary rule:
8 General exclusion
(1) In any proceeding, the Judge must exclude evidence if its probative value is outweighed by the risk that the evidence will—
(a) have an unfairly prejudicial effect on the proceeding; or
(b) needlessly prolong the proceeding.
(2) In determining whether the probative value of evidence is outweighed by the risk that the evidence will have an unfairly prejudicial effect on a criminal proceeding, the Judge must take into account the right of the defendant to offer an effective defence.
The weighing exercise in subsection (1) was introduced into our evidence legislation by the Evidence Amendment Act (No 2) 1980. This stated in s 18:
18 Court may reject unduly prejudicial evidence
Notwithstanding sections 3 to 8 of this Act [the Evidence Act 1908], where the proceeding is with a jury, the Court may, in its discretion, reject any statement that would be admissible in the proceeding under any of those sections, if the prejudicial effect of the admission of the statement would outweigh its probative value, or if, for any other reason, the Court is satisfied that it is not necessary or expedient in the interests of justice to admit the statement.
Obvious differences are the elimination of the description of the weighing exercise as a discretion, and the introduction of the word “unfairly” to qualify “prejudicial effect”. Another change is the omission of the reference to the interests of justice.
In relation to the current provision, the Law Commission said of probative value:
Probative value will depend on such matters as how strongly the evidence
points to the inference it is said to support, and how important the evidence
is to the ultimate issues in the trial.
As to unfair prejudice, the Commission said:
There must be an undue tendency to influence a decision on an improper or illogical basis, commonly an emotional one; for instance, graphic photographs of a murder victim when the nature of the injuries is not in issue. Evidence will also be unfairly prejudicial if it is likely to mislead the jury; for example, if it appears far more persuasive than it really is, as is occasionally the case with some types of expert and statistical evidence. The judge will need to consider whether any misleading tendency can be countered by other evidence that is likely to be available, or by a suitable direction to the jury. Whether evidence has an unfairly prejudicial effect must be considered in terms of the proceeding as a whole, and not just from the point of view of a particular party or a defendant.
A similar weighing exercise applies to propensity evidence pursuant to s 43(1) of the Evidence Act 2006. This was brought to attention recently in Brooks v R, where, in refusing leave to appeal, the Supreme Court quoted from its earlier decision, the leading authority:
“ When a judge is considering the extent of any unfair prejudicial effect on the defendant [under s 43], the judge should examine whether the fact that the propensity evidence is prior acquittal evidence gives rise to any, or any additional, unfair prejudice. To the extent that it does, the judge should consider how that additional dimension affects the overall balance between probative value and unfair prejudice ...”. [emphasis added]
It is this “overall balance” that is, I suggest, a misuse of the metaphor of weighing. The section uses the word “outweighs”, and the only rational interpretation in context is that it means that the risk of an unfairly prejudicial effect on the defendant is negligible; it is contextually insignificant insofar as there is no real risk of trial unfairness. Unfortunately, outweigh also means to be greater or more significant than, and this tempts the reader to invoke a balancing metaphor. Although this weighing exercise is cemented in legislation, and therefore must be applied when it is relevant, it is appropriate to note that, when understood as necessitating balancing, it has been criticised as requiring a comparison of things that are not comparable. While it is easy to accept that probative value can have metaphorical weight, unfair prejudice is something that either exists or it doesn’t, and it is not apt to think of it as having weight.
The origins of this weighing exercise are in the common law, as applied to New Zealand indirectly via the Privy Council’s decision in Noor Mohamed v R (British Guiana):
“... the judge ought to consider whether the evidence which it is proposed to adduce is sufficiently substantial, having regard to the purpose to which it is professedly directed, to make it desirable in the interests of justice that it should be admitted. If, so far as that purpose is concerned, it can in the circumstances of the case have only trifling weight, the judge will be right to exclude it. To say this is not to confuse weight with admissibility. The distinction is plain, but cases must occur in which it would be unjust to admit evidence of a character gravely prejudicial to the accused even though there may be some tenuous ground for holding it technically admissible. The decision must then be left to the discretion and the sense of fairness of the judge.”
This is not a balancing exercise. It reflects what had been said in R v Christie, about there being a “practice of a very salutary nature” that had “long existed” (although there is apparently no confirmation of that in the law reports)of the judge inviting the prosecutor not to persist in adducing evidence that, although legally admissible, would operate unfairly against the defendant. Lord Moulton said:
“Under the influence of this practice, which is based on an anxiety to secure for everyone a fair trial, there has grown up a custom of not admitting certain kinds of evidence which is so consistently followed that it almost amounts to a rule of procedure.”
Christie is often referred to as the source of this exclusionary common law evaluative judgement, but it was not expressed there as a weighing exercise. Nevertheless, evidence legislation internationally often adopts the weighing formula, although the United Kingdom legislation now avoids a weighing model in favour of a requirement that evidence must not be admitted if admission would have “such an adverse effect on the fairness of the proceedings that the court ought not to admit it.”
Our Law Commission has, in a report in 2008, had more to say about this:
“7.55 The so called “weighing” of probative value and risk of prejudicial effect required by these provisions needs some elucidation. It is something of a shorthand expression, picked up and carried forward from the common law into the statute. As a matter of logic, probative force and prejudice are incommensurables. The comparison is not one of like with like. What really occurs is that the judge evaluates the probative strength in the trial of the evidence, and also the degree of risk of an unfair trial through prejudice if it is admitted. The effect of each on the fair trial process then is evaluated, and a value judgement is made based on the interests of justice....
“7.56 ...What matters in the “weighing” exercise is whether the evidence carries a risk of prejudice relative to probative value which goes beyond the bounds of the legitimate by creating an unacceptable degree of risk of an unfair trial. ... will the propensity evidence be given greater force than it could properly warrant, bolstering an otherwise weak Crown case? It is the risk of “illegitimate” prejudice which is the concern; and at which the weighing exercise is directed.”
This amounts to acknowledging that the legislation is not to be applied literally. It is “so called” weighing, needing “some elucidation”, it is “something of a shorthand expression”, “carried forward from the common law”. The Commission seems to be wishing that courts could “elucidate” the legislation in the same way they can alter the common law by explaining it. This explanation of the weighing exercise (“what really occurs”) amounts to a new model for the decision process. Although perhaps acceptable – but that may be being generous - for the time in which it was made, it needs to accommodate the recognition in the Supreme Court of decisions which the Commission does not cite, upholding the absolute nature of the right of the defendant to a fair trial.
The Law Commission’s 2013 Review
When it reviewed the working of the Evidence Act in 2013, the Law Commission appears not to have received submissions on whether the balancing model should be retained or amended. The issues relating to propensity evidence that were considered were in effect a repetition of the discussions in Mahomed v R. The Commission did not criticise the Court’s view that there is little difference between the “balancing” exercises in s 8 and s 43(1),while noting that there is “at least [a] theoretical” difference if the balance is determined to be equally poised. Importantly, the Commission concluded that it was not prepared to countenance any approach that would give rise to a risk of unfair trials, and this governing principle led it to reject submissions that were directed at linking (by a so-called “tit for tat” rule) the permitting of a defendant to cross-examine a complainant in a sex case about previous sexual history with permission to lead evidence of a defendant’s past sex offence convictions.
In dealing with the hypothetical example of the balance being “equally poised” while at the same time upholding the need to avoid giving rise to a risk of unfair trials, the Commission overlooked the level of risk to trial fairness posed by an equal balance. A likelihood of unfairness of 50% would be regarded as too great a risk of unfairness. The decision should be exclusion when the likelihood of unfairness is much lower. The hypothetical example really asked what happens when the balance is on the boundary between admission being fair and not fair.
In assessing this risk of unfairness the judge will have regard to the likely efficacy of any instruction that the jury may be given about the proper use of the evidence and any warning about avoiding its improper use.
Prior acquittal evidence
Acquittal does not mean innocence. It could be consistent with proof of guilt but only to the insufficient standard of the balance of probabilities. When finding facts in a criminal trial, the balance of probabilities will be sufficient in deciding what evidence to accept and what to reject. Of course, the combined effect of the evidence that is accepted is the basis for the verdict, and a verdict of guilty requires the combined effect to be proof beyond reasonable doubt.
This means that evidence given at a defendant’s earlier trial where the verdict was not guilty can be adduced if it is relevant as propensity evidence in a subsequent trial for a different offence. This does not infringe the rule against double jeopardy because at the subsequent trial the defendant is not in jeopardy of conviction for the conduct that was the subject of the earlier trial. Brooks and Fenemor (above) were cases of this sort. The focus is on what the defendant claims to be prejudice that is unfair: there must be “something about the circumstances of or leading to the acquittal which gives rise to prejudice that is unfair”.
The split in the Court of Appeal in Brooks over whether there was unfair prejudice, is an indication of how difficult this evaluative judgement can be. The majority, Miller and Simon France JJ, said this about unfair prejudice in this context, and held that none had been demonstrated:
“ Following Fenemor, a defendant may be able to point to something about a previous acquittal which makes the admission of evidence tending to prove the same allegation unfairly prejudicial for purposes of s 43. That may arise where admission of the evidence forces the defendant to adduce evidence showing how the acquittal came about.
“ By way of illustration, the defendant may have offered a successful alibi, as noted above, and will need to re-establish it. Defence witnesses may now be unavailable. The record of the first trial may establish that the evidence was seriously deficient in some way, [citing RPG v R 2015] NZCA 275] or a key witness lacked credibility. [citing Blackburn v R  NZCA 365 and R v Edwards  2 All ER 266 (Crim App)] (If that witness is to give the propensity evidence, the evidence may also be of low probative value for s 43 purposes.) The defendant may also show that the need to call evidence bearing on the acquittal contributes to a risk that the propensity evidence will overwhelm the trial, unduly influencing the fact-finder.
“ We accept that in such a case unfair prejudice may result where a police or trial file is unavailable and the relevant evidence cannot be established in another way. That conclusion is consistent with the authorities. [...] However, following Fenemor , the court will not assume that the mere absence of a file is prejudicial. The defendant must both point to something about the acquittal that is relevant and show that the absence of the file is prejudicial.”
However, Peters J was unable to agree that there was no unfair prejudice in this case. Effective cross-examination was not possible because of passage of time and the absence of a proper record:
“ First, there is the matter of delay and its adverse effects on the accuracy of memory [, at  and ; and at .] The fact that this Court noted Mr Brooks' inability to recall details of his earlier trial is significant to me.
“ Secondly, almost all relevant contemporaneous information was unavailable, that is, the information from the police investigation and trial. Of course, this could occur in respect of any documents relevant to propensity evidence, but in this case it comprised the notes of evidence, police job sheets, notebook entries and (subject to what is said below) witness statements and/or briefs of evidence. [The Detective], the officer in charge of J's trial, gave evidence that these documents would have existed, but could not now be found or that (former) [another detective], the officer in charge of the S trial, had advised that the documents had been destroyed. Also, the video of Mr Brooks' own police interview was unavailable and a transcript of it which appeared to have been prepared was also unavailable. In fact, the only available contemporaneous information of consequence comprised the witness statements and briefs of evidence of S and a related witness, D. The Crown provided these documents to S and D prior to trial to refresh their memory. Even then, each was unable to recall matters of detail when giving evidence.”
At least there was no suggestion here that if propensity evidence had a high probative value it could only be outweighed by prejudice that had an even greater value. Unfairly prejudicial evidence is evidence which gives rise to an unacceptable risk of trial unfairness, regardless of how much probative value it may have.
Evidence Code and Commentary (NZLC R55 Vol 2 1999) at C58.
Compare McHugh J in Pfennig v R  HCA 7, (1995) 182 CLR 461 at 528, , almost making the same point: “...The use of the term ‘outweigh’ suggests an almost arithmetical computation. But prejudicial effect and probative value are incommensurables. They have no standard of comparison. The probative value of the evidence goes to proof of an issue, the prejudicial effect to the fairness of the trial. In criminal trials, the prejudicial effect of evidence is not concerned with the cogency of its proof but with the risk that the jury will use the evidence or be affected by it in a way that the law does not permit. In no sense does the probative value of evidence disclosing propensity, when admitted, outweigh its prejudicial effect. On the contrary, in many cases the probative value either creates or reinforces the prejudicial effect of the evidence. In my view, evidence that discloses the criminal or discreditable propensity of the accused is admitted not because its probative value outweighs its prejudicial effect but because the interests of justice (181 cf. Lord Morris in Boardman (1975) AC at 439) require its admission despite the risk, or in some cases the inevitability, that the fair trial of the charge will be prejudiced.” The reason given in this last sentence is now not correct if the defendant’s right to a fair trial is absolute.
R v Christie  AC 545.
Condon v R  NZSC 62,  1 NZLR 300 at . The Report was published in May 2008 yet does not cite Condon. Subsequently in Mohamed v R  NZSC 52,  3 NZLR 145, (2011) 25 CRNZ 223 at  per McGrath and Tipping JJ it was said that under s 43(1) ‘the only relevant prejudicial effect which logically needs to be considered is the likely impact on the fairness of the trial from the point of view of the defendant.”
Aside from that point, the Commission agreed that if this theoretical situation were to occur, s 8 would require admission (as the probative value was not outweighed), while for propensity evidence s 43(1) would require exclusion (as the probative value did not outweigh the risk of unfairness).
 Brooks v R  NZCA 280 (the post-trial CA judgment, not currently freely available online).