Efficacy of expert evidence

Helen Roebuck DNA expert witness sitting at a desk in front of lap top giving evidence

“White coat effect”

The efficacy of evidence at trial, is undoubtedly predicated on how that evidence is perceived by jurors, and the court. The preparation of inherently complex scientific and forensic evidence must be purposeful and meticulous.

It is critical that evidence presented to the jury is clear, simple and readily understood.

 “ Surprisingly little is known about ways that juries resolve differences of opinion between competing scientific forensic experts. Concerns have been raised that juries defer unduly to scientific experts and are susceptible to the ‘white coat effect’. “ [1]

In November 2023, I participated in a presentation to Juris Doctor and law students at Newcastle University alongside Jane Goodman-Delahunty.

My participation sought to assist students with preparation for evidence in chief, and cross examination specifically pertaining to expert evidence. The process was facilitated by the construction of a mock hearing involving DNA evidence.

Professor Jane Goodman-Delahunty is a prolific researcher, author and educator on the “white coat effect”, providing highly useful insights to the various sectors of the judicial system.

Insights that may prove useful in court;

Improving jury understanding and use of expert DNA evidence [2] ;

Mock jurors with less formal education achieved lower DNA knowledge scores and learned less than their more educated counterparts. Although conviction rates did not vary by educational level, educational background influenced their understanding of the scientific evidence. Less knowledgeable mock jurors were more prone to convict.

• Increased DNA knowledge reduced the force of DNA evidence.

• The conviction rate was highest for mock jurors with the least DNA knowledge.


Prior knowledge and educational background should be considered in regard to a juror’s ability to understand complex forensic evidence and render appropriate verdicts in line with that evidence.” [2]

[1] Jane Goodman-Delahunty and Kosuke Wakabayashi – Adversarial Forensic Science Experts: An Empirical Study of Jury Deliberation.

[2] Jane Goodman-Delahunty Lindsay Hewson – Improving jury understanding and use of expert DNA evidence.