I Spy with My Little Eye: Jurors' Detection of Internal Validity Threats in Expert Evidence

This experiment examined whether jury-eligible community members (N = 223) were able to detect internally invalid psychological science presented at trial. Participants read a simulated child sexual abuse case in which the defense expert described a study he had conducted on witness memory and suggestibility. We varied the study's internal validity (valid, missing control group, confound, and experimenter bias) and publication status (published, unpublished). Expert evidence quality ratings were higher for the valid versus missing control group version only. Publication increased ratings of defendant guilt when the study was missing a control group. Variations in internal validity did not influence perceptions of child victim credibility or police interview quality. Participants' limited detection of internal validity threats underscores the need to examine the effectiveness of traditional legal safeguards against junk science in court and improve the scientific reasoning ability of lay people and legal professionals.