By Andrew Roberts
The question of how and by whom the reliability of expert testimony should be evaluated is problematic. For many, the prevailing approach in Australia is a cause for concern. However, the recent case of Honeysett v The Queen  HCA 29 presented the High Court with an opportunity to grasp the nettle. In that case, the issue was whether and how a jury could be assisted in comparing the image of the accused taken at a police station to an armed robber captured on a CCTV image whose head was covered by a hood by an anatomy professor pointing out similarities in the images and the absence of any differences.
In criminal trials witnesses are generally prohibited from expressing opinions on matters that are to be determined by the jury. Witnesses are generally expected to testify only to the facts. The drawing of inferences from those facts is the exclusive province of the jury. Opinions offered by witnesses are excluded because they are superfluous. The prohibition is subject, however, to significant exceptions, one of which permits an opinion to be expressed by a witness who possesses ‘specialised knowledge’ — provided that the opinion is ‘wholly or substantially based’ on that knowledge. Such witnesses are allowed to express opinions because the jury is thought to lack the knowledge and experience that would enable it to draw rational and reliable inferences. In such circumstances, the expert’s opinions are required to ensure that verdict returned by the jury is the product of sound reasoning.
Why reliability matters
What then of the issue of reliability? If the justification for allowing experts to offer opinions is that the jury lacks the competence required to draw the inferences drawn by the expert, is the idea that evaluation of the reliability of expert opinion should be left to the jury plausible? Continue reading