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Wayne Law Review



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first hand knowledge, opinion, expert testimony


Two characteristic principles of Anglo-American evidence law are the requirement that witnesses testify only to their personal observations (the "first-hand knowledge" rule) and the prohibition against witnesses testifying to their inferences (the "opinion" rule). However, a longstanding exception to these principles permits witnesses possessed of skill or learning to draw inferences, often from facts they have not personally observed. Because such expert opinion testimony is exceptional, it is hedged about with various restrictions in addition to those such as relevancy which apply to all testimony. The predicate for admission of expert opinion testimony generally consists of two elements. First, the subject matter should be appropriate for expert opinion; i.e., it should involve questions beyond the ordinary experience and knowledge of the jurors, so that expert inferences would assist the jury. Second, the expert witness must be qualified by knowledge, skill, experience, training, or education to draw the inferences which will assist the jury. Unless at least these two criteria are met, expert testimony will not be admissible in any jurisdiction. Where an expert is asked to give an opinion on causation or prognosis, a number of jurisdictions add the further condition that the opinion be stated with some degree of certainty. This rule, which in practice has its most frequent application to expert medical witnesses, is the subject of the present Article. As used herein, the term "rule of certainty" refers to a rule which conditions the admissibility of expert opinion testimony upon the testimony's explicitly or implicitly satisfying a given standard of certainty. Under such a rule the opinion may not be considered by the trier of fact unless the expert is willing to express the requisite degree of confidence in it. The standard applied varies widely among the states. For this reason, and because the question can frequently appear in federal court litigation, the rule of certainty would seem to be an appropriate concern of the Proposed Federal Rules of Evidence, although it has not yet been included in any of the drafts promulgated. This Article will first survey the rule in its various forms, then analyze it with a view to suggesting a reformed federal rule, and, finally, consider the Erie problems involved in adopting the proposal as a federal rule of evidence.

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