4 ms·

See also: R v T (Footwear Mark Evidence) http://www.bailii.org/ew/cases/EWCA/Crim/2010/2439.html http://www.bailii.org/ew/cases/EWCA/Crim/2010/2439.html (which

by SEMW 14y ago

See also: R v T (Footwear Mark Evidence) http://www.bailii.org/ew/cases/EWCA/Crim/2010/2439.html http://www.bailii.org/ew/cases/EWCA/Crim/2010/2439.html (which is redacted to hide the appellant's identity, giving the judgment a delightfully dystopian feel). There it was held that an expert witness shouldn't use Bayesian reasoning to calculate probabilities to tell a jury "outside the field of DNA (and possibly other areas where there is a firm statistical base)". I think that, by a 'firm statistical base', the court's getting at the sort of situations where the right prior is a widely agreed on (such as DNA, where the size of the DNA database is known), so there won't be much opportunity for different expert witnesses to disagree on probabilities due to having different priors. (N.B. IANAL) This is still nonsense, IMHO. I can understand the court not wanting juries to be overly swayed by a spuriously precise probability that might have been very different if a different expert had been chosen. But there's no justification for restricting the statistical methods that the expert uses to reach their conclusion, however it's expressed to the jury. Interestingly, that case shared one of the appeal judges from the case in TFA (Lord Justice Beatson, then Mr Justice Beatson).

diminoten 14y ago
I think the distinction being made here is the difference from using statistical methods for determining overall guilt versus using statistical methods for determining specific facts about the case. We use statistics to say that someone was or was not at the scene of a crime (DNA testing doesn't 100% guarantee that a persons' blood is actually a match), for example. We don't make the leap that since they were there, "odds are" they did it, however.
- SEMW 14y ago
  The question in R v T that Bayes theorem was being applied to was a specific, factual one: whether a footprint could have been made by a particular shoe.

by SEMW 14y ago

diminoten 14y ago

I think the distinction being made here is the difference from using statistical methods for determining overall guilt versus using statistical methods for determining specific facts about the case. We use statistics to say that someone was or was not at the scene of a crime (DNA testing doesn't 100% guarantee that a persons' blood is actually a match), for example. We don't make the leap that since they were there, "odds are" they did it, however.

SEMW 14y ago
The question in R v T that Bayes theorem was being applied to was a specific, factual one: whether a footprint could have been made by a particular shoe.