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Understanding reliability in the context of admissibility of evidence

Justice Chris Maxwell, evidentiary reliability of expert evidence, Daubert, SCOTUS, PCAST, gatekeeper role of the trial judge.
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In the jurisdictions in Australia governed by the legislation, the act requires that the expert witness must have, quote, specialized knowledge based on the person’s training, study or experience, and secondly, that the opinion she gives must be, quote, wholly or substantially based on that knowledge. In other words, you’ve got to be an expert and you can’t stray outside your expertise. Crucially, reliability of the scientific opinion is not a condition of its admissibility. And Australia in that regard is in striking contrast to the UK and Canada. But as I said, even if it’s relevant, the evidence might be excluded if its probative value is outweighed by the danger of unfair prejudice.
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That is, if it’s likely to be given more weight than it deserves. But a recent decision of our top court decided that reliability is not a matter for the judge and ultimately it’s for the jury to decide whether evidence is reliable. Now, at common-law, there’s been some examination of what it means to say scientific evidence is reliable. One approach was to ask whether the subject matter of the expert opinion was part of a body of knowledge or experience, which was, quote, sufficiently organized or recognized to be accepted as a reliable body of knowledge or experience. In other words, is this established as a field of science?
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And if it is, an expert who belongs to that field will be accepted as having the requisite knowledge. In contrast, in the United States in Daubert, the US Supreme Court said that expert evidence must be both relevant and reliable. And for that purpose, the court must decide whether the principles and methodology underlying the opinion are scientifically valid. For that purpose, the court should consider whether the theory or technique being relied on has been tested, whether it’s been subjected to peer review and publication.
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What’s known about the error rate in the application of this technique, whether there are standards maintained, which control the operation and application of the particular scientific technique, and whether the technique has attracted widespread acceptance within a relevant scientific community. In a case involving scientific evidence, evidentiary reliability will be based on scientific validity.
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The purpose of the gatekeeper function is to ensure that useful and reliable scientific evidence is admitted and that unreliable and unfairly prejudicial expert evidence is excluded. As I’ve said, at its worst, unreliable expert evidence can lead to innocent people being convicted. The Supreme Court of the US in Daubert described the gatekeeper role as, involving a preliminary assessment of whether the reasoning or methodology underlying the experts testimony is scientifically valid and whether that reasoning or method can be applied to the facts in issue in this case. The Canadian Supreme Court has said that the trial judge should take seriously this role of gatekeeper.
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The admissibility of the experts evidence should be scrutinized at the time it’s put forward and not allowed too easy an entry on the basis that all of its frailties can be investigated at the end of the evidence rather than at the gateway. Gatekeeper role requires the judge to make an assessment of reliability at the admissibility stage rather than leaving such technical issues for the jury. And the reason for that is pretty obvious.
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As the President’s Council of Science and Technology noted, jurors have little ability to assess the probative value of science and the potential prejudicial impact is unusually high because jurors are likely to overestimate the probative value of a match between a crime scene sample and something taken from the accused. But if judges are to be effective gatekeepers, they need more scientific training. And it’s been noted in a number of jurisdictions that there is no scientific training for judges. And understandably, a judge is likely not to understand sufficiently the strengths and vulnerabilities of forensic science evidence offered during a trial.
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In its twenty sixteen report, the US President’s Council of Advisors on Science and Technology highlighted concerns relating to the reliability of forensic evidence, a landmark report. The report focused particularly on feature comparison methods, that is, methods which seek to determine whether a crime scene sample is or isn’t associated with a source sample, typically from a suspect based on similar features. Now, that report examined a range of feature comparison methods, DNA analysis, bitemark analysis, latent fingerprint analysis, firearms analysis and footwear analysis, as well as hair comparison. DNA analysis was found to be valid and reliable, fingerprint analysis to have valid methodology, but no other forensic method was found to have proven foundational validity.
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Now, what foundational validity means is that the method on which the expert’s opinion is based rests on reliable principles and methods. That is, the underlying science is reliable and that requires empirical studies which show the methods to be repeatable, reproducible and accurate. There’s no clear threshold for establishing foundational validity. In some cases, a high error rate won’t necessarily lead to invalidity. But it’s critical that limitations such as the error rate in the method are communicated and the implications understood so that they can be taken into account in assessing admissibility. Then we turn to validity as applied. The method must have been applied in the way it’s been validated. Has the expert reliably applied these principles and methods in practice?
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And is this expert capable of relying, reliably applying the method and doing so in circumstances like the case at hand? This is about the expert’s proficiency, and the expert needs to disclose assumptions, limitations and error rates. The focus of that US report was on proven reliability and empirical testing. And this is something that the scientific and legal sectors have a shared responsibility to ensure that only valid and reliable opinions are placed before the court.

In a case involving forensic evidence, why should evidentiary reliability be based on scientific validity of such evidence?

After watching the video, we encourage you to look at the legal provision on expert evidence in your jurisdiction with the following points in mind:

  • Does it specify the areas of expertise (such as science, art, etc)?
  • Does it mention the criteria for who qualifies as an expert?
  • Does it specify the criteria for admissibility of such opinion?
  • Does the legal provision create a strong framework for examining the reliability of expert evidence?

Share your comments below.

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Decoding Forensics for Legal Professionals

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