Canadian Law of Evidence/Utility of Evidence

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Evidence provides a means of allowing facts to be proved for the purpose of litigation. Evidence is only admissible if it is both material and relevant. Evidence can often have the side-effect of creating prejudice, and if the prejudicial effect is more significant than the probative value, it might be ruled inadmissible for that reason.

[edit] Relevance and Materiality

Evidence can only be used in a trial if it is relevant. Relevant evidence has a tendency to make the existance of a fact more/less probable than it would without the evidence. For example, the existence of fact A makes fact B more/less likely, than if A did not exist. Relevance depends on the purpose for which the evidence is tendered. Thus,it might be admitted for one purpose but not for another. For example, the criminal record of an accused can be tendered for the purpose of establishing, say, character, but it cannot be used to consider the probability that he or she committed a crime. The judge decides if tendered evidence is relevant. The test is largely pragmatic and based on the judge's appreciation of the issues in dispute. A decision as to the relevance of evidence is a decision on a matter of law.

In addition, relevant evidence must be "material". Its relevance must go towards proving a fact that is of consequence to the trial. That is, there must be a relationship between the evidence and a legal issue put to the court.

That said, all evidence can be material in one of two ways. It can be either "direct" or "circumstantial". Direct evidence is evidence that supports a proposition directly at issue in case. For example, finger prints at a murder scene in a criminal trial, or a signed contract in a civil trial. Circumstantial evidence, however, is evidence that can be used to infer a conclusion. For example, a sighting of the accused in the neighbourhood at the time of the crime. One type is not necessarily stronger than the other.

Circumstantial evidence is the result of combining seemingly unrelated facts that, when considered together, can be used to infer a conclusion.

[edit] Probative value

The degree of relevance is called "probative value" of the evidence. The "probative value" becomes important when issues immerge around the appropriateness of the evidence. Given the limited time allocated to a case, less probative evidence will often be overlooked in order to present more valuable evidence. Probabtive value of evidence is often of particular importance when a particular piece of evidence is also prejudicial to the accused. Certain evidence can inappropriately influence triers of fact as it appeals to their emotions or baises. The positive value of evidence must be weighed against the potential hostility or sympathy that it may create.

The case of R. v. Morris illustrates the relation between relevance and probative value. The issue was whether a newspaper clipping on the heroin trade, found at the bedside of the accused, should be admitted as evidence. The Court allowed it, stating that all relevant evidence must be admitted. It is up to the trier of fact to determine its probative value.

Admissibility of evidence must not be confused with weight. If the article had concerned the heroin trade in Hong Kong, it would of course have greater probative value. If the article had been a manual containing a step-by-step guide to importing heroin in to Vancourver from Hong Kong, the probative value would be greater still."

When selecting evidence several questions should come to mind:

• Does fact X make proposition Y more/less likely? (eg. is a person wearing a lampshade as a hat relevant to determine if that person is drunk?)
• If so, to what degree? (eg. would there be any other reasons outside of intoxication that a person would wear a lampshape?)
• Does proving proposition Y help decide legal issue Z? (eg. is a person's state of drunkeness an issue in a case of assault?)

[edit] Prejudicial effect

Although the first rule of evidence is to admit all relevant evidence there are certain types of relevant evidence that should not be admitted as it will have a prejudicial effect on the fairness of the trial. It is said that there are three grounds of excluding evidence on the basis of it prejudice: "moral", "logical", and "time".

First, there is evidence of moral prejudice which has the potential of creating outrage in the jury and could influence them to make their decision based on emotion. For example, a jury may get the urge to punish an accused for past bad acts even though they are not at issue in the trial. Second, there are logical prejudices that suggest to the jury to make improper inferences, such as relating the accused race with a particular disposition. Last, there is evidence that is prejudicial to time and resources. The jury should not have their time wasted with minor evidence that will waste their time and confuse them from the real issues.

All judges have a discretion to exclude any evidence on the basis that its prejudicial effect will out-weigh the probative value.