Validity and Relevancy Analysis: An Approach to the Admissions of Experimental Evidence

Rules of evidence in the common law system were developed to serve the fundamental purpose of minimizing erroneous factual conclusions by the jury. In pursuit of this goal, two guiding principles have been followed: first, that the jury should be provided with the most accurate and trustworthy information possible; second, that the flow of information to the jury should be controlled to exclude evidence which is irrelevant or otherwise misleading. Since the earliest cases in which the results of experiments were offered as evidence, American courts have treated experiments as a unique form of evidence but have found it difficult to formulate a rational and workable rule for the admissibility of experimental results. Because the courts have never undertaken the thorough analysis necessary to harmonize the uniqueness of experimental evidence with basic evidentiary principles, the present rationale for determining the relevancy and admissibility of experimental evidence is incomplete and unsatisfactory. This Comment begins with a discussion of validity and the scientific experimental method, and then progresses to an examination of relevancy. A final section on admissibility synthesizes the validity and relevancy discussions, and suggests first that "similarity" concepts are improperly applied to validity, and second that, even in the context of relevancy, "similarity" principles should be reconsidered. A new rationale is proposed, based upon the relationship between the experimental hypothesis, the defining postulate of the experiment, and the disputed factual issue, rather than upon random and undiscriminating similarity of conditions. It will also be shown that a careful validity analysis facilitates the evaluation of probative worth and the consideration of the evidence on secondary exclusionary grounds.