R v Carol Mathey (2007) VSC 398

A judge ruled that if evidence tendered as expert opinion evidence is to be admissible, it must be agreed or demonstrated that there is a field of ‘specialised knowledge.’  There must be an identified aspect of that field in which the witness demonstrates that by reason of specified training, study or experience, the witness has become an expert.   Opinions proffered must be ‘wholly or substantially based on the witness’s expert knowledge.’

So far as the opinion is based on facts ‘observed’ by the expert, they must be identified and admissibly proved by the expert, insofar as the opinion is based on ‘assumed’ or ‘accepted’ facts, they must be identified and proved in some other way, it must be established that the facts on which the opinion is based form a proper foundation for it; and the opinion of an expert requires demonstration or examination of the scientific or other intellectual bases of the conclusions reached: that is, the expert’s evidence must explain how the field of ‘specialised knowledge’ in which the witness is expert by reason of ‘training, study or experience’, and on which the opinion is ‘wholly or substantially based’, applies to the facts assumed or observed so as to produce the opinion propounded.