There has been so much of confusion and conflict in expert testimony; so much discussion and difference of opinion as to the true province of the medical expert, especially in homicidal cases, and the subject has become so involved in the minds of medico-legal jurists.
Here are some of the clear statements represented with reference to great books according to the law of America.
An expert is one who has made the subject upon which he gives his opinion a matter of study, practice, or observation, and he must have a particular and special knowledge upon the subject concerning which he testifies.
Expert evidence is that testimony given by one, expert and specially skilled, in the subject to which it relates, or is applicable; concerning information beyond the range of ordinary observation.
The witness must only state facts and not draw conclusions or inferences from facts
It has been held that to allow witnesses to draw conclusions from facts or inferences is to usurp the province of the court or jury, and is illegal
Medical expert witnesses are doctors, nurses, surgeons, or other qualified professionals who have the knowledge and experience to testify on a specific medical field. Attorneys frequently use medical expert witnesses in personal injury and medical malpractice cases at the discovery and trial stages.
Medical experts are frequently called upon to testify in personal injury and medical malpractice cases on a variety of matters directly connected to their professional experience. These topics may include care standards, the origin of injuries, and the long-term effects of medical conditions.
While medical expert witnesses were more closely identified with courtroom witness, an excellent expert adds value at every level of the litigation process. The observations of a medical expert witness, for instance, might help attorneys assess the merits of a case before litigation. Expert study and testimony are also required as your case moves through discovery and, eventually, trial.
While these are the general rules of law, there are exceptions where the opinions of skilled experts may be taken as before stated
Opinion evidence is the conclusions or opinions of witnesses concerning propositions based upon ascertained or supposed facts, by one who has had superior opportunities and greater knowledge than the ordinary person or witness, to judge of the subject-matter of the inquiry, and who, by reason of his especial knowledge of, and experience with the subject, is believed to be capable of arriving at a better and more reliable conclusion and judgment, from facts within his own knowledge, concerning the questions involved in the inquiry or controversy.