Opinion Evidence at Trial

When an individual testifies as a witness their primary job is to testify about facts that are within their knowledge. Generally speaking, the court is not interested in a witness’s opinion on particular facts.
That is because, in general, witnesses are not experts capable of making an informed opinion on a particular matter. Moreover, statement by witnesses based on their opinion alone can be very confusing for the jury.
The jury may be tempted to substitute the witness’s opinion on the value of facts presented at evidence for their own opinion or inferences. Because of this, opinion evidence is generally inadmissible at trial. This means that witnesses are prohibited by the rules of evidence from asserting their own opinion as part of their oral testimony.
There are two exceptions to the rule against opinion evidence. The first exception pertains to everyone and the second exception pertains only to individuals who are testifying as recognized experts on a particular topic of interest to the court.
The rule governing opinion expert by a non-expert, or “lay person” was first articulated by the Supreme Court of Canada in the case of Graat v. R. Mr. Graat was charged with impaired driving.
The main issue at trial was whether or not Mr. Graat was, in fact, impaired at the time he was pulled over and apprehended by the police. During Mr. Graat’s trial, the Crown called a number of officers to testify that Mr. Gaat was impaired.
The court took issue with the fact that these officers were not experts in determining whether or not an individual is impaired. In the end, the court concluded that the officer’s were allowed to express their opinion that Mr. Graat was intoxicated because their use of the term “intoxicated” was really just a “short-form” way of expressing a set of observations (slurred speech, lack of balance or coordination, impaired motor skills, etc.)
However, the court took the opportunity in Graat to place limits on the type of opinion evidence a person who is not an expert may express in a court of law.
The court ruled that a lay person cannot give opinion evidence on a legal issue. For example, a lay person could not express the opinion that a defendant was “negligent” because the term “negligent” has a specific legal meaning and it is the role of the judge to determine a legal issue such as negligence in the course of a person’s trial.
Whether or not an individual is intoxicated, on the other hand, is not a legal question because there is no special legal definition for the term “intoxicated”.
Rather, this is a concept that is in the everyday knowledge and experience of the average person, and, as such, a lay person should posses the requisite knowledge and experience to express an opinion on the topic of intoxication.
The court was also careful to caution that since the police are only using the term “intoxicated” to indicate a number of observations usually consistent with intoxication and are not using this term because they are experts at determining when an individual is intoxicated, their testimony should be given no more weight than the testimony of an average person who is not a police officer.
Graat tells us that lay persons can give opinion evidence on a matter which is within their knowledge and experience so long as the jury knows that their opinion is not to be given any special weight.
The jury should treat the witness’ opinion as if they are using a short form that denotes a number of observations. The matter on which the witness is giving opinion evidence should also be within the knowledge and experience of the jury.
In other words, these are matters of common knowledge. When the witness says “the defendant was drunk”, what he or she means is “when I encountered the witness I observed several things that people commonly associate with drunkenness”. It is still open to the defence to question the witness’ opinion by attacking its reliability.
For example, the defendant’s criminal defence lawyer could suggest that the witness themselves was intoxicated at the time so that their opinion is unreliable.
Or, they may suggest that the indicia of intoxication relied upon by the witness could be explained by other circumstances- nervousness, or a physical handicap. In this way, the criminal defence lawyer suggests to the witness other innocent explanations for the accused’s apparent intoxicated demeanor.
In Sherrard v. Jacob the court identified a number of issues, other than intoxication, that a lay person could give opinion evidence in relation to in court.
These include: identification of handwriting, persons and things, (ii) apparent age of a person, (iii) the bodily plight or condition of a person, including death or illness, (iv) the emotional state of a person, e.g., whether distressed, angry, aggressive, etc., (v) the condition of things, e.g., worn, shabby, used or new, (vi) certain questions of value, e.g., how much something is worth, and (vii) the estimation of speed and distance.
These are all matters which can be said to be of common knowledge, and which the jury and the witnesses would likely have knowledge and experience.
Experts are often called to give their opinion at criminal trials on a number of matters within their field of expertise. For example, psychiatrists are asked to give their opinions as to the mental state of an individual involved in the crime, pathologists are called to give their opinion on the results of the autopsy, and crime scene experts are called to give their opinion on the inference to be drawn from evidence at the crime scene.
Experts can be called as a witness in almost any subject that is beyond the knowledge and experience of the average person if their assistance clarifies any of the legal matters in issue and will be of assistance to the trier of fact. Expert evidence can be an essential aspect of a criminal trial. It can also be a very dangerous type of evidence.
The danger in expert evidence lies in the fact that the expert witness can sometimes come very close to usurping the role of the jury. In a criminal trial, the jury is charged with making factual determinations regarding all questions of fact that arise in the course of the trial.
This means that the jury, after listening to all the evidence tendered before it, is supposed to make the final decision on issues such as the mental state of the parties involved, the time of death, the series of events at the crime scene, etc.
When an expert testifies, the jury may fall into the trap of uncritically accepting what the expert has to say. This could happen because the jury is blown away by the expert’s credentials and are of the opinion that a person who has studied the topic so thoroughly cannot possibly be wrong.
However, this can also happen because expert witnesses tend not only to be experts in their field of study but also experts at being witnesses. Most expert witnesses are in court frequently. As a result, they present very well to the jury.
Moreover, as the opposing lawyer is probably not an expert in the field, it is quite difficult for the opposing lawyer to cross-examine the expert witness in any meaningful way.
As a result, the testimony of expert witnesses often goes into the record unquestioned. Since the ladies and gentlemen of the jury are not experts in the field it is nearly impossible for them to recognize mistakes or holes in the expert’s evidence.
Another problem with expert evidence is that the Crown has an overwhelming advantage when it comes to obtaining the services of an expert.
The Crown has a list of expert witnesses who they use regularly. Moreover, expert witnesses are very expensive. While the Crown has unlimited resources to pay expert witnesses, individual defendants often have trouble affording expert witnesses.
Nevertheless, expert evidence is admissible in court. However, the dangers of expert evidence forced the Supreme Court to come up with a test to determine when expert evidence should be admitted at trial.
In R. v. Mohan the court said that admission of expert evidence depends on the application of four criteria:1. Relevance: evidence that is otherwise logically relevant may be excluded if (i) the evidence would cause the jury to be unduly prejudiced against the defendant and this concern undermines any value that may be added by the evidence, (ii) the evidence involved would take an inordinate amount of time to present and that this time is not justified by its value, and (iii) the evidence is misleading in the sense that its effect on the jury is misleading. 2. Necessity in Assisting the Jury: the court must consider whether the evidence is likely to assist the jury or confuse the jury and whether the jury is likely to evaluate it critically or be so overwhelmed by the credibility of the expert that they accept his or her testimony at face value. 3. The Absence of an Exclusionary Rule: the court must ensure that the evidence is not prohibited by any other rule of evidence. 4. The Expert Must Be a Properly Qualified Expert: an expert must adduce proof that he or she is properly qualified as an expert. An expert can become an expert not only through education but also through working in a field for a number of years.
When an expert testifies about their opinion in court they will generally be basing their opinion on a scientific theory. For example, psychologists after use tests or look for specific indicators to determine whether a person suffers from a particular mental disorder.
However, some scientific theories are more reliable than others. A good example is evidence gathered through a process of hypnosis.
There is no general scientific agreement about whether hypnosis is effective or valuable. Before admitting a expert’s opinion in court, the court must be satisfied that the scientific theory on which the expert bases his or her opinion is sound. In Daubert v. Merrell Dow Pharmaceuticals Inc., the United States Supreme Court generated a test to determine whether a scientific theory or technique is sound. In R. v. J. (J.-L.) the Supreme Court of Canada adopted this test, known as the Daubert test, as part of Canadian law.
As a result, all courts use the Daubert test to decide whether or not to admit evidence based on a particular scientific theory at trial. In order to admit evidence based on a particular scientific the court must consider:(i) whether the theory or technique has been tested by other experts, (ii) whether the theory or technique has been subject to peer review and verification, (iii) if there is a known or potential error rate and the existence or maintenance of standards controlling the technique’s operation (in other words, whether scientists have tested the theory and determined what percentage of the time it is successful), and (iv) whether the theory is generally accepted by the scientific community. Only a well tested theory that is generally accepted by scientists will be admissible in court.
Despite the safeguards the Supreme Court has placed on expert evidence, the danger of this type of evidence remains, as we saw in the recent scandal surrounding Dr. Charles Randall Smith. Dr. Smith was a Toronto doctor who testified in a number of cases as an expert on “shaken baby syndrome”.
Shaken baby syndrome is a common cause of death in infant homicide cases. It occurs where an adult aggressively shakes a baby and that shaking leads to the baby’s death. At some point, Dr. Smith crossed a line where he stopped forming objective opinions on whether or not the baby had died from shaken baby syndrome and began testifying that shaken baby syndrome was the cause of death in cases where the signs of the syndrome were not there. Instead of maintaining a scientifically neutral position, Dr. Smith became a professional advocate and his opinion became tainted by a desire to ensure that abusive parents were punished. In 2009 a coroner’s review found that Dr. Smith made questionable conclusions that the cause of death was shaken baby syndrome in at least 20 cases, 13 of which likely resulted in wrongful convictions.
Though Dr. Smith was no doubt driven by compassion, his zealous desire to hold someone responsible for the death of these babies resulted in grave injustice. The story of Dr. Smith exemplifies the real danger of expert testimony if used improperly in the courtroom.
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