The courts have given many different reasons for their decision to exclude expert testimony on eyewitness reliability. Some of these reasons been summarized by Fulero (1993):
(1) eyewitness unreliability is a matter of 'common sense', 'ordinary experience', or 'common knowledge'; (2) the issue can be adequately addressed in cross-examination; (3) the testimony invades the province of the jury; (4) doubt as to the scientific basis of the testimony; (5) miscellaneous procedural problems; (6) the exclusion was harmless or did not affect the results; (7) there was no abuse of discretion in the exclusion of the testimony; (8) the individual who was to testify was not an expert; (9) the matter can be adequately addressed by jury instruction; (10) methodological problems with the empirical studies; (11) the prejudicial effect of the testimony outweighs its probative value; (12) the testimony would 'amount to a lecture to the jury on how to do its duty'; (13) expert psychological testimony is not admissible to impeach the credibility of a witness.
In addition, since the late 1960s several US higher court decisions (see the listing provided by Ebbesen and Konecni, 1996) and some eyewitness memory researchers (e.g. Ebbesen and Konecni, 1996; Elliott, 1993; McCloskey and Egeth, 1983) have questioned whether expert testimony on eyewitness reliability is: a proper subject matter; a waste of the court's time; conforms to a generally accepted explanatory theory; would assist the trier of fact; whether the scientific research findings are reliable and accurate and are based on forensically-related situations and populations; whether admitting the evidence would overwhelm, confuse or mislead the jury; whether such evidence would make jurors overly skeptical and inclined to reject the testimony of eyewitnesses (thereby lowering the number of false convictions but also increasing the number of erroneous acquittals); and whether the possibility that admitting expert testimony would open the gates to conflicting testimony which would degenerate into an acrimonious, confusing, and uninformative 'battle of experts'.
When trial judges' judgements to exclude are appealed, appellate courts seldom find that there has been an abuse of discretion because of the wide latitude trial judges are given in making evidentiary rulings (Fulero, 1993). In contrast, when courts permit expert testimony on eyewitness reliability they do so because: the research is seen as reliable and valid; is generally accepted by the scientific community; the research would assist the average juror in that it would contradict lay persons' common-sense beliefs; there would be no invasion of the province of the jury as the jury remains free to reject the expert testimony in whole or part; and the eyewitness identification of the defendant is a key element of the prosecution's case but is not substantially corroborated by evidence giving it independent reliability.
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