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Proper Seat: A Bayesian Discussion of the Position of Expert Witnesses

NCJ Number
114627
Journal
Law and Human Behavior Volume: 12 Issue: 4 Dated: (December 1988) Pages: 499-510
Author(s)
W A Wagenaar
Date Published
1988
Length
12 pages
Annotation
Using the framework of Bayesian decision theory, this article distinguishes between opinions formed in the minds of the members of a court and the information on which these opinions are based, as supplied by expert witnesses.
Abstract
Expert witnesses should in principle do no more than provide information that may help the court form opinions. They must never attempt to provide the final opinions themselves. The expert's subjective opinion could be part of the information supplied but should not relieve the court of its obligation to form its own opinion. The difference between opinions and information is elucidated by the framework of Bayesian decision theory. Within this framework, opinions are represented by prior and posterior odds. The court's decisionmaking process is the revision or formation of opinion on the basis of evidence or the transformation of prior odds into posterior odds using a likelihood ratio. When the task of expert witnesses is limited to providing information (likelihoods in Bayesian terminology), the danger that social scientists will misrepresent the reliability of their knowledge or make biased statements is not larger than in the normal conduct of their science. 16 references. (Author abstract modified)

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