How is Credibility Determined?
At trials Judges are often required to decide which witnesses they believe. In other words, they must assess the credibility of each witness who testifies. This can be particularly challenging of course. Judges don’t have any sort of superpower to determine who is being truthful. What they do have is experience and the benefit of each witness having their evidence tested through cross-examination to assist in determining who to believe, if anybody. Sexual assault cases in particular, can commonly fall to be determined purely on an assessment of credibility.
Frequently people will ask how judges decide who to believe. They will often think that any inconsistency in a witness’ account no matter how small ought to be fatal. This is not the case. Judges will not expect perfection from a witness. Minor inconsistencies on peripheral matters are unlikely to detract from a witness’ credibility.
Credibility involves an assessment of the trustworthiness of a witness’ testimony based upon the veracity or sincerity of a witness and the accuracy of the evidence that the witness provides
The art of assessment involves examination of various factors such as:
- the ability and opportunity to observe events, the firmness of their memory,
- the ability to resist the influence of interest to modify their recollection,
- whether the witness’ evidence harmonizes with independent evidence that has been accepted,
- whether the witness changes their testimony during direct and cross-examination,
- whether the witness’ testimony seems unreasonable, impossible, or unlikely,
- whether a witness has a motive to lie, and
- the demeanour of a witness generally
Ultimately, the validity of the evidence depends on whether the evidence is consistent with the probabilities affecting the case as a whole and shown to be in existence at the time.
The testimony of each witness must be carefully scrutinized not only on its own merits, but also in the context of the totality of the evidence
The credibility and reliability of a witness’ evidence must be tested in the context of all of the other evidence together, particularly where the Crown's case depends solely on the unsupported evidence of the complainant and the principal issue is that witness' credibility and reliability.
The court must also be mindful of the danger of accepting the evidence of a complainant on the basis of demeanour alone. As noted by the BC Court of Appeal:
The credibility of interested witnesses, particularly in cases of conflict of evidence, cannot be gauged solely by the test of whether the personal demeanour of the particular witness carried conviction of the truth. ... the real test of the truth of the story of a witness in such a case must be its harmony with the preponderance of the probabilities which a practical and informed person would readily recognize as reasonable in that place and in those conditions: Faryna v. Chorny, [1951] 2 B.C.J. No. 152
In the end, credibility assessments are far more art than science.