If I have a matter where an owner sues a builder because part of the owner's house which the builder constructed has collapsed, does the owner need an expert to help prove it was the builder's fault? If I have a matter in which a business is claiming lost profit because of negligent investment advice, can the Court work out for itself if the advice was negligent? Can a Court reach conclusions on the loss caused in relation to the above actions without the evidence of an expert?
An opinion is any inference from observed facts. It is normally the role of the judge and jury to draw inferences from facts which are given in evidence by witnesses. The witnesses are not normally allowed make inferences themselves. However, in certain circumstances the judge and jury may not be equipped to make the appropriate inferences without the assistance of an expert witness because of the special knowledge an expert may possess based on his or her training, study or experience.
Dixon CJ in Clark v Ryan  HCA 42 considered that an expert is not entitled to give opinion evidence on matters the jury was capable of deciding for themselves. In particular His Honour said:
The rule of evidence relating to the admissibility of expert testimony as it affects the case cannot be put better than it was by J. W. Smith in the notes to Carter v. Boehm. "On the one hand" that author wrote, "it appears to be admitted that the opinion of witnesses possessing peculiar skill is admissible whenever the subject-matter of inquiry is such that inexperienced persons are unlikely to prove capable of forming a correct judgment upon it without such assistance, in other words, when it so far partakes of the nature of a science as to require a course of previous habit, or study, in order to the attainment of a knowledge of it." Then after the citation of authority the author proceeds: "While on the other hand, it does not seem to be contended that the opinions of witnesses can be received when the inquiry is into a subject-matter the nature of which is not such as to require any peculiar habits or study in order to qualify a man to understand it." Adopted by Harding A.C.J. in Reg. v. Camm.
In R. v. Parker, one of the cases establishing the evidentiary use of finger prints to prove identity, Cussen J. in that connexion said that expert witnesses may give in evidence statements based on their own experience or study but that they cannot be permitted to attempt to point out to the jury matters which the jury could determine for themselves or to formulate their empirical knowledge as a universal law. To this should be added the observation made by Vaughan Williams J. during the argument of Reg. v. Silverlock, viz. "No one should be allowed to give evidence as an expert unless his profession or course of study gives him more opportunity of judging than other people." The words "profession or course of study" have of course a wide meaning and application; see per Lord Russell C.J. The evidence of Mr. Foster Joy included much that offended against these principles. Some of it was evidence of opinion that lay outside any qualifications that upon any view however benevolent he could be supposed to possess. Some of it was an attempt to guide the jury upon matters which it was within the ordinary capacity of jurors to determine for themselves. Perhaps particular pieces of evidence may be picked out concerning the behaviour of the kind of semi-trailer the defendants Clark drove but Mr. Foster Joy wa not qualified by practical experience to give evidence of their behaviour in fact. In short no small part of his evidence was outside the range of opinion evidence by experts and as to more still Mr. Foster Joy was not a qualified expert. The objection to its admissibility should have been sustained. (citations omitted)The above case is referred to in Rees v Lumen Christi Primary School  VSC 514 (17 November 2010) at  by Robson J. Rees has a useful discussion of admissibility of expert opinion evidence.
I have addressed the two examples above as follows:
- Building collapse: this could be a claim in negligence against the builder which alleges a breach of a duty of care. Two opinions may be required here: an expert opinion on how the breach of duty occurred (e.g. poor design, poor workmanship or use of inferior materials) and another expert opinion on the value of loss (e.g. rectification cost, loss of value of property). These opinions are required as the appropriate inferences relating to liability and loss could only be drawn by a Judge (and jury, if one is requested) with the assistance of an expert with special knowledge.
- Loss of profit by negligent investment advice: this could be a claim for negligent misstatement. Two opinions may be required here: an expert opinion on whether the advice was below a particular standard of care in that industry and another expert opinion on the extent of the loss, based on a review of the financial information of the business. Once again, these opinions are required as the appropriate inferences relating to liability and loss could only be drawn by a Judge (and jury, if one is requested) with the assistance of an expert with special knowledge.
- Cross on evidence.
- Odgers Uniform evidence law in Victoria.