Dateline: September, 2010, Issue 4

How often are jurors presented invalid scientific evidence?

Daubert and other cases decided in the 1990s (e.g., Daubert v. Merrell Dow Pharmaceuticals, 1993; General Electric v. Joiner, 1996; Kumho Tire v. Carmichael, 1999) require that judges base admissibility decisions for forensic scientific evidence on its scientific validity as opposed to relying entirely on its general acceptance in the professional community.

Research shows that judges do not fully understand the Daubert factors, admitting evidence that is scientifically flawed and excluding evidence that is valid.

Gatowski and colleagues (2001) conducted a national survey of trial court judges to assess judges' understanding of the Daubert factors. Overall, only 4-6% of judges were able to clearly define the various factors and provide appropriate examples of how they would use them in evaluating scientific evidence.

Kovera and McAuliff (2000) asked trial court judges in Florida to evaluate the admissibility of expert testimony in a sexual harassment case. Some judges were provided expert testimony based on a study that was scientifically sound. Other judges were provided expert testimony based on a study that was scientifically flawed in one of three ways - the presence of a confound, a missing control group, and experimenter bias. The presence of flaws did not influence admissibility decisions. Judges admitted the scientifically flawed study to the same extent as the scientifically sound study, and excluded the scientifically sound study to the same extent as the scientifically flawed study.

The inability to differentiate sound from flawed scientific research is not limited to judges. Kovera and colleagues (2002) found that both judges and attorneys had difficulty distinguishing sound from flawed scientific research.

Daubert does not prevent jurors from hearing invalid scientific evidence. Jurors are as likely to hear valid as flawed scientific evidence.

Source Kovera, M. B., & McAuliff, B. D. (2000). The effects of peer review and evidence quality on judge evaluations of psychological science: Are judges effective gatekeepers? Journal of Applied Psychology, 85, pp. 574-586.

Source Kovera, M. B., Russano, M. B., & McAuliff, B. D. (2002). Assessment of the commonsense psychology underlying Daubert: Legal decision makers' abilities to evaluate expert evidence in hostile work environment cases. Psychology, Public Policy, and Law, 8, pp. 180-200.