4.1 Other means of scrutinising experts

In addition to truth and validity, there are a number of other factors that fact-finders can use to assess an expert’s opinion. These include:

1. Reasons – experts are required to provide reasons for their opinions, and without these, it is difficult for a fact-finder to have confidence in the expert. In Massey v Tameside and Glossop Acute Services NHS Trust,^{Footnote 25} the court said that a lack of written explanations of how conclusions were reached had added to difficulties in resolving differences of opinions between experts.
2. Methodology – the methodology or investigation should be capable of identifying the relevant facts. For example, in Korpach v Klassen,^{Footnote 26} the court preferred a meticulous method of investigating crops compared to a ‘broad brush’ method.
3. Respectable body of scientific opinion – a theory is preferable where it is widely respected by other scientists. For example, in Petursson v Hutchison 3G UK Ltd,^{Footnote 27} the court was sceptical of an expert’s theory about the risks of mobile telephone masts to human health given that the expert’s peers were strongly critical of the expert’s theory.
4. Changes of opinion – while an expert may need to change their views if the underlying facts change, unilateral changes of opinion may be signs of unreliability. In BSkyB v HP Enterprise Services,^{Footnote 28} changes in an expert’s opinion were taken to undermine their evidence.

In this next activity, you can have a go at testing some expert opinions for truth and validity.