The Law

Expert testimony is a common and essential component in both civil and
criminal trials. Every forensic scientist who is called into court to give the
results of his or her study must first be qualified as an expert witness. Courts
allow expert testimony out of necessity to assist the fact finder. A witness
qualifies as an expert by reason of “knowledge, skill, experience, training,
or education.”1 The trial judge determines if a witness is qualified as an expert
and in what field of areas of science the expert may testify.2 The forensic scientist
may qualify as an expert on the basis of education, background, or study.3
Evidence being offered by a qualified forensic expert is subject to admissibility
standards for the specific scientific evidence being presented. A judge
must determine admissibility of that scientific evidence.
Before a judge can
make that determination, the proffered scientific evidence must first pass a
simple test of relevancy. Relevant evidence is defined by the Federal Rules of
Evidence and most state court jurisdictions as “evidence having any tendency
to make the existence of any fact that is of consequence to the determination
of the action more probable or less probable than it would be without the
evidence.”4 Once a court determines that the proffered scientific evidence is
relevant, there are two different legal standards that courts apply in determining
the admissibility of evidence: the Frye5 general acceptance standard and
the Daubert6 scientific reliability standard. The original scientific admissibility
test developed in the case of Frye v. United States7 held that, to be admissible,
scientific evidence must be “sufficiently established to have gained general acceptance in the particular field in which it belongs.”8 After the development
of the Frye general acceptance standard, federal and state courts attempted
to apply the rule to a wide variety of scientific evidentiary issues with mixed
results. Courts often struggled with the Frye standard because the inquiry did
not focus on the reliability of the particular scientific evidence; instead, the
Frye test focused upon the general reliability of the scientific testing as a whole
and its acceptance by others in the field. Another problem was that it was difficult
to identify the appropriate expert community to answer the question
of general acceptance. Some courts became concerned with the correctness
of the Frye standard because the standard unfairly discredited new tests and
accepted scientific principles. In 1993, the Supreme Court developed a new
standard for scientific evidence in Daubert v. Merrell Dow Pharmaceuticals.9
In Daubert, the Supreme Court concluded that in order for scientific evidence
to be admissible, it must be shown to be scientifically valid and relevant to
at least one issue in the case.10 The Supreme Court offered numerous factors
to aid federal judges in making the determination of scientific admissibility.
These factors included whether the technique has been or can be tested,
whether the technique has been subjected to peer review or publication, the
known or potential rate of error, whether the technique is generally accepted
in the community, and whether the technique was created outside of the
litigation process. The Daubert test still allows courts to consider the issues
addressed in the Frye standard because the “generally accepted” prong is one
of many factors—instead of the sole factor in the analysis. By replacing Frye
with Daubert, the U.S. Supreme Court made the trial judge a “gatekeeper” for
the admissibility of any scientific evidence11 (see Chapter 16).