This study examined the ability of jury-eligible community members (N = 248) to detect internal validity threats in psychological science presented during a trial. Participants read a case summary in which an expert testified about a study that varied in internal validity (valid, missing control group, confound, and experimenter bias) and ecological validity (high, low). Ratings of expert evidence quality and expert credibility were higher for the valid versus missing control group versions only. Internal validity did not influence verdict or ratings of plaintiff credibility and no differences emerged as a function of ecological validity. Expert evidence quality, expert credibility, and plaintiff credibility were positively correlated with verdict. Implications for the scientific reasoning literature and for trials containing psychological science are discussed.
KeywordsScientific reasoning; Internal validity; Expert testimony; Juror decision-making Recent advances in DNA, blood type, and fingerprint testing have increased the likelihood that average citizens will confront complex scientific evidence when serving as jurors in civil and criminal cases. Nearly two-thirds (65%) of state court judges responding to a national survey indicated that they had some experience with DNA evidence in their courtrooms (Gatowski, Dobbin, Richardson, Ginsburg, Mertino, & Dahir, 2001). The role of psychological science in the legal system has burgeoned recently as well. Social or behavioral scientists constituted nearly one-quarter of all scientists in U.S. criminal appellate cases involving expert testimony from 1988 to 1998 (Groscup, Penrod, Studebaker, Huss, & O'Neil, 2002).Research examining laypeople's scientific reasoning skills has enjoyed renewed interest among social scientists and legal scholars due to several recent U.S. Supreme Court rulings on the admissibility of expert evidence (Daubert v. Merrell Dow Pharmaceuticals, Inc 1993; General Electric Co. v. Joiner, 1997; Kumho Tire Co. v. Carmichael, 1999). Daubert and its progeny have entrusted judges with a gatekeeping role in which they should base their admissibility decisions on the relevance and reliability of the expert evidence. Despite the Court's confidence in judges' ability to fulfill their gatekeeping role, many judges lack the scientific literacy required for a Daubert analysis (Gatowski et al., 2001) and have difficulty identifying methodologically-flawed expert testimony (Kovera & McAuliff, 2000a). Attorneys also struggle to effectively evaluate expert evidence (Kovera & McAuliff, 2000b). Their ability to make and successfully argue motions to exclude junk science, crossexamine an expert, or consult their own expert may be limited as a result (Kovera, Russano, & McAuliff, 2002).Based on these limitations, it is likely that at least some invalid research will reach laypeople serving as jurors in court. Can they recognize variations in the validity of psychological science? We examined this research question by presenting jury-eligible community m...
