The impact of psychological expert testimony in child sexual abuse cases

While the admissibility of psychological expert testimony varies from one common law country to another, evidentiary analyses dealing with the impact of such testimony are invariably opinion-based and lack empirical support. Predictions from theoretical models of communication/persuasion processes suggest that psychological expert testimony in child sexual abuse cases may be given considerable weight by jurors, but the experimental literature investigating the impact of such testimony is scant. This thesis reports four experiments designed to investigate the juridical impact of psychological expert testimony in a simulated child sexual abuse case, using gender-balanced juries throughout. In the first study, presence or absence of a psychologist's generalised testimony concerning children's cognitive abilities was varied across three ages of child victim/witness. Subjects viewing the expert testimony rated the child higher on memory ability, resistance to suggestion and reality monitoring ability and gave higher ratings of defendant guilt. In the second experiment, the same expert testimony was presented by male and female experts in either an adversarial or nonadversarial role. Significant interaction effects indicated that, for the male expert only, ratings of the dependent variables were significantly lower in the adversarial role. The third experiment investigated whether expert testimony presented before and after the child's testimony is differentially utilized. Ratings of the child-based variables and verdict ratings did not differ as a function of the sequence of testimony, but regardless of temporal order, presence of expert testimony led to significantly higher child-based ratings than the absence of such testimony.In the fourth experiment, the differential impact of three types of expert testimony were studied; testimony concerning children's general cognitive abilities, testimony concerning characteristic behavioural reactions to sexual abuse, and testimony assessing the validity of the child's statement. The quality of the child's statement was varied, using content-based criteria. Subjects viewing the cognitive abilities testimony rated the child higher on memory, resistance to suggestion and reality monitoring, but there were no significant differences on verdicts by type of testimony. Those who viewed the child's enhanced statement gave higher ratings of defendant guilt on the aggravated sexual assault charge. Results indicated greater acceptance but less scrutiny of nonadversarial expert testimony. In all four studies, the prime predictor of child credibility and verdict ratings were the jurors' perceptions of whether the child had misinterpreted the defendant's actions. Juror gender effects were also consistent in all studies, with females more likely to rate the child's credibility higher and to find the defendant guilty. In general, results indicated that psychological expert testimony which details research findings concerning children's cognitive abilities seems less likely to change verdicts than to increase the degree of certainty felt by those voting guilty, and may therefore serve to improve the juridical decision-making process. The impact of psychological expert testimony appears to vary with expert role when the psychologist is male. Changing the order in which testimony is presented appears to have no significant impact on verdicts or jurors' perceptions of the child witness. The implications of the thesis findings for psychological theory and legal practice are discussed.