Unit 19 Opinion Evidence and Experts

Question 1

What is the general rule for witness evidence?

Answer 1

The general rule is that witnesses may only give evidence of facts they personally perceived and not evidence of their opinion, i.e. evidence of inferences drawn from such facts.

Question 2

What are the two exceptions to the general rule that witnesses must not express opinions (i.e. give only evidence of facts)?

Answer 2

a. Non-experts. A statement of opinion on any matter not calling for expertise, if made by a witness as a way of conveying relevant facts personally perceived by him or her, is admissible as evidence of what the witness perceived.

b. Experts: a statement of opinion on any relevant matter calling for expertise may be made by a witness qualified to give such an expert opinion.

Question 3

May expert evidence be accompanied by animations?

Answer 3

Yes, where appropriate to illustrate the opinion.

Question 4

If there is an objection as to the admissibility of expert opinion evidence, who must prove its admissibility?

Answer 4

If objection to the admissibility of expert opinion evidence is made, it is for the party proffering the evidence to prove its admissibility.

Question 5

What is the prima facie position on expert opinion evidence?

Answer 5

Unless the admissibility is challenged, the judge will admit the evidence as sufficient safeguards are provided by the rules on pre-trial disclosure.

Question 6

Is Non-Expert Opinion Evidence allowed?

Answer 6

A statement of opinion may be given by a witness, on a matter not calling for expertise, as a compendious means of conveying facts perceived by the witness.

Thus an identification witness is not required to give a description of the offender or some other person, leaving it to the tribunal of fact to decide whether that description fits the accused or other person identified, but may express an opinion that the accused (or other person) is the person the witness saw on the occasion in question. Likewise, a non-expert may give evidence of opinion to identify an object (e.g. a picture), handwriting with which he or she is familiar, or a voice which he or she recognises or with which he or she is familiar.

Question 7

What can non-experts give opinion evidence on? (examples)

Answer 7

A non-expert may give evidence of opinion to identify:

• a person,
• an object (e.g. a picture),
• handwriting with which he or she is familiar, or
• a voice which he or she recognises or with which he or she is familiar,

or give evidence of:

• a person’s age,
• of the general appearance of the person’s state of health, mind or emotion;
• the speed of a vehicle;
• the state of the weather;
• the passage of time.

Question 8

Is scientific evidence required to identify a prohibited drug?

Answer 8

Although scientific evidence is not always required to identify a prohibited drug, police officers’ descriptions of a drug must be sufficient to justify the inference that it was the drug alleged

Question 9

What kind of evidence can a non-expert give in relation to drunk driving?

Answer 9

Fitness to drive when drunk needs an expert but a non-expert may give evidence as to his impression of whether A had been drinking, provided he describes facts on basis of which he formed impression

Question 10

How is the competence of an expert W determined?

Answer 10

(1) Statute sometimes prescribes qualifications needed (e.g. two experts needed to acquit on grounds of insanity)

(2) Proper qualification on an area is a Q for the court

(3) Decision usually made on written material (in rare cases may hold a voir dire)

(4) Judge has power to remove a W’s expert status

(5) Competence may stem from formal study/training, experience or both

Question 11

What is the duty of those instructing expert witnesses?

Answer 11

Those instructing expert witnesses should satisfy themselves as to their expertise and engage an expert of suitable calibre.

Question 12

What is the court’s duty when expert witnesses are instructed?

Answer 12

Whether a witness is properly qualified in the subject calling for expertise is ultimately a question for the court. Courts need to be scrupulous to ensure that evidence proffered as expert evidence is based upon specialised experience, knowledge or study: mere self-certification is insufficient.

Question 13

Is a police officer competent to give expert evidence of the practices and associations of gangs if admissible as bad character evidence?

Answer 13

Yes if the officer has made a sufficient study, whether by formal training or through practical experience, to acquire a balanced body of specialised knowledge not available to the jury; simple, and not necessarily balanced, anecdotal experience will not suffice.

Question 14

What matters call for expert evidence?

Answer 14

Expert opinion evidence may only be received on a subject calling for expertise, which a lay person, such as a magistrate or a juror, could not be expected to possess to a degree sufficient to understand the evidence given in the case unaided.

Question 15

Is it possible to call expert evidence on a matter on which the tribunal of fact can form its own opinion without the assistance of an expert?

Answer 15

No - such expert opinion evidence is inadmissible because it is unnecessary.

Question 16

What is the duty of an expert witness?

Answer 16

• Help court to achieve OO by giving objective, unbiased opinion. This duty overrides any obligation to the person instructing the expert or by whom the expert is paid.
• Comply with court directions
• Inform court at once of any significant failure to take step required by a direction
• When giving evidence, must:
  (i) Define area of expertise (and in report)
  (ii) Draw court’s attention to any Q outside of his expertise
  (iii) Inform all parties and court if his opinion changes from that in the report
• Should also give court necessary criteria for testing validity of conclusion

Question 17

What directions must the judge give in relation to EE?

Answer 17

• Misdirection to tell jury that EE should be accepted if uncontradicted
• If EE on ultimate issue (e.g. on whether A meets diminished responsibility threshold), must be made clear to jury that they are not bound
• However, if jury reject unchallenged EE, must be for a reason
• Cannot direct jury that they may disregard scientific evidence when only a scientist is qualified to answer the Q (I keep forgetting this)

A direction of the following kind can be made: ‘Where, as here, there is no dispute about findings made by an expert you would no doubt wish to give effect to them, although you are not bound to do so if you see good reason to reject them.’

Question 18

What is the principle regarding expert evidence and diminished responsibility (murder)?

Answer 18

Two clear principles emerged from the cases, on the issue of diminished responsibility:

a. if there were no other circumstances to consider, unequivocal, uncontradicted medical evidence favourable to an accused should be accepted by a jury and they should be so directed; and

b. where there were other circumstances to consider, the medical evidence, though it be unequivocal and uncontradicted, must be assessed in the light of the other circumstances.