What makes for a good expert in court?  There are many components.  But in the civil courts it is the judge who has to assess the expert evidence and who decides, where there is a disagreement, which expert’s evidence to prefer (on the balance of probabilities).

A leading exposition of the judge’s process in carrying out this task was given by Lord Justice Stuart-Smith in his judgment in Loveday v Renton[1]  when he explained how “the court has to evaluate the witness and the soundness of [the expert] opinion.”  No better and more complete explanation has been given since.

The judge identified a number of important factors which will be taken into account in deciding whether to accept or reject the expert’s evidence:

1. The reasons given by the expert for his or her opinions and the extent to which they are supported by the evidence.
2. The internal consistency and logic of the expert’s evidence.
3. The care with which the expert has considered the subject and presented the evidence.
4. The precision and accuracy of thought as demonstrated by the answers to questions.
5. The nature of the response to searching and informed cross-examination.
6. The extent to which the expert faces up to and accepts the logic of a proposition put in cross-examination or is prepared to concede points that are seen to be correct;
7. The extent to which an expert has conceived an opinion and is reluctant to re-examine it in the light of later evidence, or alternatively demonstrates a flexibility of mind which may involve changing or modifying opinions previously held.
8. Whether or not an expert is biased or lacks independence.
9. The expert’s demeanour in the witness box.

Experts are often surprised at this list, its length and particularly the idea that demeanour might play a role (along with inconsistency or an over-rigidity of thought).  But as can be seen in court judgments again and again, between them these ‘tests’ will provide the judge with the ability to explain, sometimes in rather robust language, why one expert’s opinion has been rejected.

To avoid failing one of these ‘tests’, an expert must not only be sure of the grounds relied on to support an opinion, but must have carried out adequate preparation before giving evidence (including providing a well-structured report in the first instance).  Further the expert will also benefit from understanding how cross-examination is structured and how to give a good and effective account of him or herself in the witness box.

It is not enough for the expert in court simply to rely on the belief that he or she is right!

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[1] [1990] 1 Med LR 117 at page 125