Apart altogether from fixed rules of exclusion, judges have the discretion to exclude relevant and material evidence where its probative value is outweighed by its "prejudice." In considering the exclusionary discretion, a judge must determine the value of the evidence, based on both its believability and the strength of the inferences it leads to, against the costs presented by such evidence, including things as diverse as the practicalities of its presentation, the fairness to the parties and to witnesses, and the potentially distorting effect the evidence can have on the outcome of the case. Because of full answer and defence considerations, defence evidence
should be excluded solely where the risks of prejudice substantially outweigh its probative value.
Even in the absence of an exclusionary rule requiring its rejection, logically relevant evidence may be excluded through the exercise of judicial discretion. The extent to which the Supreme Court of Canada has endorsed the existence of this discretion has varied over time. For most of the past century judges were considered to have little or no discretion to exclude technically admissible evidence.29This was because the "rule of law" and common law theory are intrinsically wary of discretion. Discretion imports choice, and it is better that persons be ruled by law and not by the choices of other people. Moreover, discretion can confuse the roles of the trier of law and the trier of fact.
In spite of these concerns, for the reasons described above,30we are currently in an era of strong discretion in which the judge is often given a vital role to play in evaluating evidence as a prelude to admissibility. The law has now come to recognize two, sometimes overlapping, kinds of exclusionary discretion.
One gives judges the discretion in criminal cases "to exclude evidence obtained in circumstances such that it would result in unfairness if the evidence was to be admitted at trial."31This discretion gained its feet in Canada through the influence of the Charter and is now said to be grounded both in the constitution and the common law. Since this discretion is most likely to be invoked where evidence has been unfairly or illegally obtained,32it is discussed in this book along with the exclusionary remedy.33The other form of discretion, more intimately linked to questions of relevance, permits judges to exclude otherwise technically admissible evidence in criminal, civil,34and administrative law cases,35where the benefits of its admission cannot justify the negative effects its admission will cause. In R. v. Mohan, Sopinka J. spoke of a "cost-benefit analysis" - "that is ‘whether its value is worth what it costs,’"36with the
"costs" concept describing the vast array of negative implications admission can cause. In the language of the cases, evidence can be excluded as a matter of discretion where its prejudice (or costs) outweighs its probative value, even where that evidence otherwise complies with the rules of admissibility.37Judges even retain the discretion to exclude evidence that satisfies the technical requirements of statutory rules of admissibility, such as section 71538(providing for the admission of prior testimony) and section 715.1 of the Criminal Code39(providing for the admission of videotaped statements by children about sexual offences), and section 12 of the Canada Evidence Act40(providing for the convictions of a witness to be proved).
At common law, there had been no recognized discretion to exclude technically admissible defence evidence.41In R. v. Seaboyer, the Supreme Court of Canada changed the law by recognizing that such discretion exists, but emphasized that it is to be applied in an extremely guarded fashion. The Court noted that defence evidence should not be excluded simply because its probative value is outweighed by the prejudice it could cause. It can be excluded solely where its probative value is substantially outweighed by the prejudice it could cause.42The more imposing standard for excluding defence evidence is related to the long-standing belief that it is better to produce an inaccurate acquittal than a wrongful conviction. This requires that the accused be given the benefit of every doubt, including in the application of rules of proof. As Justice Rosenberg explained in R. v. Clarke, the protection of the innocent and the right to present full answer and defence depend on the ability to call evidence.43While there is discretion to exclude otherwise admissible evidence, the law of evidence furnishes no "inclusionary" discretion. In other words, if evidence does not satisfy the rules of admissibility, a judge is
not empowered to receive it. Having said this, the exclusionary rules are, in some cases, applied more leniently in order to allow the admission of important defence evidence. Martin J.A. recognized in R. v. Williams that "a court has a residual discretion to relax in favour of the accused a strict rule of evidence where it is necessary to prevent a miscarriage of justice and where the danger against which an exclusionary rule aims to safeguard does not exist."44To be clear, this is not to say that the rules of proof do not apply to accused persons. They do. It is just that there will be cases where we can reduce the risk that we will convict innocent people by applying the rules of evidence loosely rather than strictly.
In R. v. Felderhof45Justice Rosenberg raised the interesting possibility that while the law of evidence does not allow technically inadmissible evidence to be received, the Charter might. He suggested that inadmissible defence evidence could perhaps be admitted by way of Charter remedy, if doing so would remedy state action that made a trial unfair. A possible example might be if state action were to deprive the accused of the testimony of a defence witness. A court in such circumstances might be prepared to accept hearsay evidence as a substitute, even where that hearsay evidence would not otherwise have been admissible. In appropriate cases this could be a preferable remedy to staying the proceedings entirely.
To decide whether the costs outweigh the benefits, or whether the probative value of evidence outweighs its prejudice, a judge must come to some appreciation of the probative value of the evidence. This evaluation presents the risk in jury trials that the judge will do the jury’s job. As indicated, the weight to be given to evidence has generally been considered as a matter for the trier of fact or the jury. What is a judge to consider, then, in assessing the probative value of evidence? Can the trial judge evaluate both the "believability" and the "informativeness" of the evidence?
There is no controversy that the judge is to assess how "informative" the evidence is. If it does not address a live issue or its cogency is questionable, or even if the evidence is redundant, exclusion is more likely. The controversy...