Before the testimony of an expert witness is admitted, he must be qualified as an expert; in other words it must be shown by his own testi mony that he has a knowledge derived from experience or study not possessed by the or dinary persons in regard to the particular sub ject to which he intends to testify. Whether or not the witness has proved himself an expert is determined by the trial judge in his discretion.
The method usually adopted to get the tes timony of an expert witness before the jury, after his qualification, is through the form of a hypothetical question. A question is put to the witness by the counsel of the party calling him, the question containing in detail the facts which the counsel believes have been proved and the witness is asked his opinion upon the assump tion that the facts assumed are true. Such hypothetical question is often of great length, containing, as it does, a statement of facts that may have required days to prove. After the question is answered by the expert, he is usually subjected to a long cross-examination by the opposing counsel to test his skill and lcnowledge and the correctness of his conclusion. That the ordinary jury places little weight upon the con clusions of an expert based upon the facts con tained in a hypothetical question may be in ferred from the fact that the counsel putting the question may assume facts which have not been proved to the satisfaction of the jury. Again the question is often so long and involved that its meaning is soon lost.
In other cases, however, where the witness has lcnowledge of the facts, the hypothetical question is not necessary. For instance, the opinion of an expert in handwriting may be given after his comparison of the disputed writ ing with an admitted sample of handwriting used as a standard of comparison; and the physician who has examined a physical injury, or the alienist who has examined a person claimed to be insane, may testify as to his opin ion based upon the lmowledge acquired by him through such examination without the medium of a hypothetical question.
The courts do not consider expert testimony of great importance, or in any case binding on the jury. It is allowed solely for the purpose
of assisting the jury and the courts take oc casion to instruct a jury to attach such weight to expert testimony as in their minds it seems entitled or to disregard it altogether if they deem fit so to do. Such an instruction will be upheld even if there is no conflict in the expert testimony introduced.
In spite of the just criticism to which the modern development of expert testimony has been subjected, the doctrine has its uses and is necessary to our system of jurisprudence.
Thus, such testimony is absolutely indispen sable to prove the custom in a trade; to prove the tensile strength of materials; the probable cost of buildings or works; the chemical com position of materials; the presence of disease and the cause and effects of disease or physical injury and the cause of death; the seaworthiness of vessels and other nautical matters; and to assist the jury in various other matters not within the knowledge of the average judge or juryman.
Various remedies through legislation have been suggested to remedy the abuses to which expert testimony has been subjected, such as limiting the number of such witnesses to be called upon a trial; limiting the length of the testimony, forbidding an expert witness receiv ing any compensation beyond the ordinary fees of witnesses and even to the extent of forbid ding expert testimony in some classes of cases, the most recent suggestion in connection with criminal cases being the creation of a board of experts retained and compensated solely by the State whose services may be invoked by either the people or the accused.
It may be suggested that the evil will, in time, work its own remedy through the agency of the courts without the aid of legislation. The judge presiding at the trial of an action has a wide discretion in allowing or disallowing the testimony of experts, and it may be said that a too liberal policy of allowing expert tes timony without limit is largely the cause of the abuse.