Toward a Trauma-Informed Approach to Evidence Law: Witness Credibility and Reliability

The truth-seeking function of Canadian courts is impaired because the current approach to assessing the credibility and reliability of witness testimony is not trauma-informed (i.e., it does not reflect what is known about the causes and impacts of psychological trauma on the individual). The adverse effects of trauma are widespread in Canadian society, particularly amongst those groups most likely to come into contact with the legal system. Unfortunately, the longstanding proposition that the assessment of witness credibility and reliability is “a matter within the competence of lay people” suffers from its reliance on “common-sense” understandings of human cognition and behaviour that contradict the scientifically proven effects of trauma.

After a review of Canadian case law and model jury instructions, we demonstrate that the rules governing two commonly used inferential “tools” used to evaluate witness testimony—impeachment by prior inconsistent statements and assessments of demeanor—are fundamentally flawed when it comes to witnesses who have experienced trauma, whether they are victim-witnesses, third party witnesses or accused persons. This has profound implications for confidence in the administration of justice in civil and criminal trials, and other forums that rely on the law of evidence. While other jurisdictions, such as the United Kingdom, have begun to address this serious error, Canada has yet to do so.