Chapter 9: Opinion Evidence

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Role of trier of fact

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evaluate the facts and determine what to make of them

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Role of witnesses

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provide facts

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27 Terms

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Role of trier of fact

evaluate the facts and determine what to make of them

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Role of witnesses

provide facts

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Witness should only state the facts that

are within their knowledge, observation, and experiences

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Opinon evidence

evidence given by a witness that is based on conclusions or inferences drawn from both facts or observations

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Starting point of opinion evidence

not admissible unless helpful for a clear understanding of testimony or it is expert opinion

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Layperson’s opinion

given by ordinary witness on matter of everyday experience

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When is opinion evidence permitted

where the opinion does not unnecessarily encroach on the trier of fact’s role

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Leading case on opinion evidence

R v Graat

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R v Graat: facts

police officers gave their opinion into the state of intoxication of the accused

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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

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Compendious mode of speaking

testimony where witness mixes opinion into their narrative in order to express themseives

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Why is compendious mode of expression allowed

sometimes it is difficult for witness to express information w/o stating the opinion

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Expert opinion

testimony given by properly qualified person with specific expertise in an area that is in issue before the court

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Why is expert opinion allowed

to assist trier of fact in coming to conclusion of facts in that area

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Expert opinion rule

permitted if specialized knowledge will permit trier of fact to better understand the facts or evidence before it

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Leading case on expert opinion evidence

Mohan

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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

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Mohan criteria

relevance

necessity in assisting trier of fact

absence of any exclusionary rule

properly qualified expert

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Mohan factors: relevance

simple, logical relevance

probative value vs prejudicial effect

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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

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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

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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

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Mohan factors: absence of exclusionary rule

can’t admit evidence that would normally be rejected if presented directly

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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

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Case of White Burgess Langille Inman v Abbott and Haliburton Co involved

professional negligence of former auditors

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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

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Exceptions to Rule against Oath Helping

child SA cases

Trauma experts to testify why someone with PTSD looks like they are untruthful