Usurping the Role of the Jury? Expert Evidence and Witness Credibility in English Criminal Trials

Abstract

The reluctance of English and other common-law criminal courts to admit expert evidence of witness credibility is rooted in two main objections: that such evidence needlessly complicates the jury's task and that it threatens to ‘usurp’ the jury's role. The ‘usurpation’ objection can be understood as referring to a risk that the expert will be accorded unwarranted epistemic authority on matters which it is important for the jury to decide for itself. These objections have substance, and although they apply to expert evidence in general they have particular force when applied to evidence of credibility. But the jury, as a responsible fact-finder, also has a duty to attend to expert evidence that will help it avoid ‘epistemic injustice’. Particularly in rape and sexual abuse cases, there are good reasons for admitting some forms of expert evidence of credibility, and concerns about ‘usurpation’ do not justify the British government's apparent abandonment of proposals to make such evidence more widely admissible in rape trials.