Professor Sir David Spiegelhalter
speaker
351 appearances
17 recordings
1 series
first heard Oct 2010
last heard Jan 2021
Professor Sir David Spiegelhalter’s voice in public audio — every appearance, attributed to the second.
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Appearances
to observe what you did see, given all these different things that might explain what's going on.
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But the crucial element is not just this.
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You also have to take into account the plausibility of the explanations themselves based on other knowledge you've got.
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It tells you how to weigh the new evidence in order to change your opinions about these competing explanations.
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Well, the classic one is the Sally Clark case, a mother who had two of her children who sadly died, and she was prosecuted for murdering the babies, and part of the evidence was how rare it was to get two cot deaths, two natural deaths, in the same family, just by chance alone.
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Now, the expert very much overestimated the rarity of this, but that's not quite the issue.
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The crucial thing is what is said is that the probability of this occurring, if she really were innocent, is really quite small.
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However, as we've heard previously, this is easily turned by the prosecutor's fallacy into a belief that that means that the chance that she's innocent is also very small.
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It's very easy to make that change in reasoning, which is completely wrong.
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We have to, by Bayesian thinking, take into account the plausibility of the other hypotheses.
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And we have to look at how likely it is, for example, that a mother would murder her two children.
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And it turns out that, if anything, that's even less likely than having two natural cot deaths in the same family.
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Yes, we have to look at the relative plausibility given all the evidence that's in front of us.
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Well, I'm very concerned about this.
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This R versus T case essentially has banned from the Court of Appeal the use of Bayes' theorem and likelihood ratios in any areas apart from DNA analysis.
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And as they said, possibly other areas where there's a firm statistical base.
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But I think this is based on a fundamental misunderstanding of how probabilities arise.
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They seem to think they're sort of completely objective facts about the world that everyone must be in complete agreement about.
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But a group of top forensic scientists and statisticians have written about this and complained about this case.
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And if I can quote from what they say, they say, "...probabilities should be informed by data, knowledge and experience.
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Showing 241–260 of 351 · page 13 of 18
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