Trial judges serve as “gate keepers” and determine whether expert testimony is admissible. They do so by applying rules set up in opinions handed down from prior cases, such as Daubert. One criteria is error rate, a test of the reliability of the techniques proffered to the trier of fact.
The National Academy of Sciences report held up DNA testing as the new “gold standard” for forensic evidence. DNA, of course has a sizeable database and experts can testify, with considerable confidence, about the likelihood that a DNA sample came from a particular individual. These data are not available for most classifications of forensic evidence.
An interesting question arises: How much error might be tolerated by a court when an expert evidence presents finding to a jury? If the expert testified the the procedure gave correct evidence 75% of the time, would a judge allow that information to be considered.
Here is an interesting news report from Texas. The court excluded evidence provided by a psychologist about error or certainty. Of course, part of the problem that the experts error rate was overestimated, but still it raises that question about degrees of uncertainty a court might permit.
Question: How certain should expert testimony be? If the expert spelled out a technique’s shortcomings and told the jury he or she was right 75% of the time, is that acceptable testimony or would it simply confuse a jury?