TRENDS IN THE OTHER CRITERIA USED TO ASSESS EXPERT EVIDENCE
So far we have focused on the reliability of expert evidence. We have examined trends in how often reliability is addressed, how often evidence is found unreliable, and what factors enter into the reliability assessment. Now we turn to the other criteria judges use to assess expert evidence: relevance, qualifications, and other considerations, Data on trends in these criteria allow us to explore whether judges have scrutinized reliability more carefully since Daubert or whether there has been nothing more than a switch in terminology. We conclude that while parties challenging evidence may have recast some challenges in terms of reliability since Doubert, there has not merely been a shift in terminology.
We begin by reviewing the definitions of the various criteria and discussing how challenges directed at one criterion may be recast as challenges directed at reliability. We then examine trends in the assessment of relevance, qualifications, and other considerations over time and interpret the findings.
BASED ON RELIABILITY
As discussed in Subsection 2.1, three major criteria enter into federal district court judges' decisions on whether to admit evidence: reliability, relevance, and qualifications. Judges also take other considerations into account, such as whether the evidence is unfairly prejudicial or is based on privileged information. In many cases, the distinctions between these criteria are blurry.
Relevance refers to whether the evidence will assist the trier of fact in determining a fact at issue. It is often difficult to distinguish an objection based on relevance from an objection based on reliability. For example consider testimony that asserts a substance causes cancer in humans based on the results of animal studies. Such testimony might be considered unreliable because it is based on research that cannot be reliably extrapolated to humans. But it might instead be considered irrelevant because the research sheds no light on whether the substance causes cancer in humans.
Qualifications refers to whether the expert has specialized knowledge in the field relevant to the testimony. It is easy to imagine how a party challenging an expert's qualifications could recast such a challenge in terms of reliability. For example, instead of arguing that the expert does not have the proper training to present evidence on a certain topic, the challenger could argue that the expert's testimony is unreliable because he or she has inadequate knowledge of the methods in the field.