JURORS USE OF PROBABILISTIC EVIDENCE

Mock jurors' use of probabilistic evidence was examined in a fractiona l factorial design manipulating 7 variables: strength of nonstatistica l evidence; quantification of nonstatistical evidence; strength of sta tistical evidence; combination of 2 pieces of statistical evidence; in struction in use of Bayes' theorem; and presentation of fallacies (bot h prosecutor's and defense attorney's) concerning use of statistical e vidence. One hundred eighty-nine subjects viewed 1 of 16 videotapes pr esenting a condensed mock trial. Subjects completed dependent measures after each of 4 witnesses and at the end of trial. The strength of bo th nonstatistical and probabilistic evidence affected verdicts; the ot her manipulations did not. Overall, subjects slightly underused the pr obabilistic evidence, as compared to their individualized Bayesian nor ms, and subjects did not succumb to fallacies. However subjects greatl y varied in over- or underutilization even after Bayesian instruction. Future research should examine use of weak nonstatistical evidence, a nd should test different probabilistic instructions.