Role of trier of fact
evaluate the facts and determine what to make of them
Role of witnesses
provide facts
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Role of trier of fact
evaluate the facts and determine what to make of them
Role of witnesses
provide facts
Witness should only state the facts that
are within their knowledge, observation, and experiences
Opinon evidence
evidence given by a witness that is based on conclusions or inferences drawn from both facts or observations
Starting point of opinion evidence
not admissible unless helpful for a clear understanding of testimony or it is expert opinion
Layperson’s opinion
given by ordinary witness on matter of everyday experience
When is opinion evidence permitted
where the opinion does not unnecessarily encroach on the trier of fact’s role
Leading case on opinion evidence
R v Graat
R v Graat: facts
police officers gave their opinion into the state of intoxication of the accused
Opinion Evidence Factors set out in Graat
witness has personal knowledge of observed facts
witness is in better position than trier of fact to draw inference
witness has necessary experiential capacity to draw the inference
opinion is compendious mode of speaking
Compendious mode of speaking
testimony where witness mixes opinion into their narrative in order to express themseives
Why is compendious mode of expression allowed
sometimes it is difficult for witness to express information w/o stating the opinion
Expert opinion
testimony given by properly qualified person with specific expertise in an area that is in issue before the court
Why is expert opinion allowed
to assist trier of fact in coming to conclusion of facts in that area
Expert opinion rule
permitted if specialized knowledge will permit trier of fact to better understand the facts or evidence before it
Leading case on expert opinion evidence
Mohan
Mohan facts
pediatrician charged with SA of 4 female patients
defence wanted to call evidence that perpetrator had certain characteristics and Mohan did not fit those characteristics
psychiatrist testified in a voir dire
evidence excluded by trial judge
Mohan criteria
relevance
necessity in assisting trier of fact
absence of any exclusionary rule
properly qualified expert
Mohan factors: relevance
simple, logical relevance
probative value vs prejudicial effect
Mohan factors in assessing PV vs PE using 3 criteria
connection between expert opinion and facts proven
strength of expert evidence
importance of the evidence
What factors does court consider in assessing prejudicial effect of opinion evidence
unwanted negative effect on the trial
effect of the evidence is out of proportion to its reality
probability of too much information overwhelming or confusing the trier of fact
Mohan factors: necessity - must be needed to allow fact finder to
appreciate technical nature of facts
form correct judgment on a matter if ordinary person are unlikely to do so w/o assistance
Mohan factors: absence of exclusionary rule
can’t admit evidence that would normally be rejected if presented directly
Mohan factors: properly qualified expert
witness must have acquired special or peculiar knowledge through study or experience in respect of the matters on which they undertake to testify
Case of White Burgess Langille Inman v Abbott and Haliburton Co involved
professional negligence of former auditors
2 step analysis adopted in White Burgess
party leading evidence must establish the threshold requirements of inadmissibility
court must decide whether the potential benefits justify the risks of admitting the evidence
Exceptions to Rule against Oath Helping
child SA cases
Trauma experts to testify why someone with PTSD looks like they are untruthful