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,[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,[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,[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,[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.

Activity 4 Which expert opinions are true and valid?

You should allow yourself 30 minutes for this activity

Compare the evidence with the expert opinion and give your view as to whether the expert opinion is true or false and whether the expert opinion is valid or invalid.

Case 1

Evidence:

Suspect was left-handed and had red hair. 10 per cent of people are left-handed and 4 per cent of people in England have red hair.

Expert opinion:

Given that 10 per cent of people are left-handed and 4 per cent of people have red hair in England, then the suspect would be one of 0.4 per cent of population.

Case 2

Evidence:

Blood type found on broken window at scene of burglary was type AB. Suspect's blood type is A.

Expert opinion:

Blood type found on broken window at scene was type AB and the suspect's blood type was found to be type B.

This evidence does not inculpate or exculpate the suspect.

Case 3

Evidence:

The speed limit was 50mph. The accused was travelling at 60mph.

Expert opinion:

Accused was travelling at 60mph in a 30mph zone. This indicates that they were driving completely inappropriately given the limits.

  • 1 Massey v Tameside and Glossop Acute Services NHS Trust [2007] EWHC 317.
  • 2 Korpach v Klassen [2000] CanLII 19612 (SK PC).
  • 3 Petursson v Hutchison 3G UK Ltd [2005] EWHC 920 (TCC).
  • 4 BSkyB v HP Enterprise Services [2010] EWHC 86 (TCC).

OpenLearn - Expert evidence and forensic science in the courtroom
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