Conviction by mathematical error?

doi:10.1136/bmj.320.7226.2

BMJ 2000;320:2-3 ( 1 January )

Editorials

Conviction by mathematical error?

Doctors and lawyers should get probability theory right

The first 150 words of the full text of this article appear below.

In a recent case of DNA evidence the probability of a chance match was quoted as 20 million to one. The accurate statement $---$ thatthe defendant or two other unknown people in the United Kingdomcould have committed the offence $---$ is much less impressive. Otherevidence was overwhelming, but this may not always be true, especiallywith matches from DNA databases. Even more problematic than theissue of presenting statistical evidence fairly is the problemof getting itwrong.

On 9 November at Chester Crown Court Sally Clark, a Cheshire solicitor, was convicted, by 10-2 majority, of smothering hertwo infant children. With conflicting forensic evidence, the Crown'scase was bolstered by an eminent paediatrician testifying thatthe chances of two cot deaths happening in this family was vanishinglysmall $---$ 1 in 73 million. This seriously misunderstands probabilitytheory. It is speculation whether Sally Clark would have beenacquitted without this evidence. But with . . . [Full text of this article]

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Rapid Responses:

Read all Rapid Responses

Misleading inferences costing money and time: Adrian Midgley
bmj.com, 1 Jan 2000 [Full text]
Conviction by Mathematical Error: A R W Forrest
bmj.com, 2 Jan 2000 [Full text]
Mathematical errors: Ken Norman
bmj.com, 3 Jan 2000 [Full text]
Registration for Civil Court experts needed too: Brian Morgan
bmj.com, 7 Jan 2000 [Full text]
Re: Registration for Civil Court experts needed too: Penny Mellor
bmj.com, 6 Jan 2000 [Full text]
Law Reform Essential: John P Heptonstall
bmj.com, 7 Jan 2000 [Full text]
Use of estimate might have been correct: Mark Friston
bmj.com, 7 Jan 2000 [Full text]
Conditional probability should be applied: Wai-Ching Leung
bmj.com, 7 Jan 2000 [Full text]
Re: Conviction by Mathematical Error: expectations grate: Ed Cooper
bmj.com, 10 Jan 2000 [Full text]
Conviction by Probability Theory: John P Heptonstall
bmj.com, 11 Jan 2000 [Full text]
Perhaps we should own up to our relative ignorance: Mark Browne
bmj.com, 31 Jan 2000 [Full text]
statistics of 'cot death': John P Heptonstall
bmj.com, 11 May 2000 [Full text]