Volume 37, Issue 4 (July 1992)
Can We Believe What We See, If We See What We Believe?—Expert Disagreement
Forensic experts often disagree. The possible sources of such disagreements are analyzed and possible avenues of resolution indicated. The logic of interpreting scenes, and pattern injuries such as bitemarks, is explained to locate potential sources for interpretive error, and to recommend strategies to avoid compounding such errors when preparing cases.
In one sense, two observers may not see the same thing, although their eyesight is normal and they are aware of the same artifact. Cases show that both practical and theoretical investigative expectations affect what count as observations. These expectations confer evidential status on the artifact. When two observer's expectations conflict, they do not see the same thing, so are not presented with the same evidence.
Expectations can be either appropriate, or inappropriate. These senses are clearly distinguished using illustrative cases. When inappropriate, they cause observational errors of a unique sort, supplying one source for disagreement. When inferences are made from these inappropriately sanctioned observations, interpretive errors are compounded and resolutions of disagreement become difficult.
These observational and inferential errors are explained, described, and illustrated with cases, along with recommendations for recognizing and avoiding them.