Why it matters in the Letby case
Named statisticians draw a direct line from Clark to the Letby case on the presentation of statistical evidence to juries.
Statistical explainer
The Sally Clark statistics lesson
Sally Clark was convicted of murdering her two sons in 1999 on statistical evidence the Court of Appeal later identified as unsafely presented. The 2003 quashing established a now-standard caution about expert statistical testimony in serious cases.
Legal explanation1Court/official
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Prosecution position
Statistical material was presented to the Letby jury as part of the case connecting her to the cluster of events.
Expert challenge / post-conviction reading
Named statisticians draw a direct line from R v Clark. Sally Clark was convicted in 1999 of murdering her two sons partly on statistical evidence; the Court of Appeal quashed the conviction in 2003 and the case established a standing caution about how statistical expert testimony is put to juries.
What remains uncertain
The two cases differ in their evidence: Clark turned on a single misused probability figure, while the Letby critique concerns the construction of an event set and the absence of a comparator. The parallel is about the mode of reasoning, not equivalence of facts.
Common questions
What happened in the Sally Clark case?
She was convicted in 1999 of murdering her two infant sons. The Court of Appeal quashed the conviction in 2003, having found the statistical evidence had been unsafely presented.
What was the statistical error?
A figure for the chance of two cot deaths in one family was presented in a way that invited the prosecutor's fallacy, and it assumed independence between the two deaths.
How close is the parallel to this case?
The parallel is about how statistical reasoning is put to a jury, not about identical facts. The critique here concerns event selection and the missing comparator rather than a single probability figure.
Did the Clark case change anything?
It produced a standing judicial caution about expert statistical testimony in serious criminal cases, which is why statisticians invoke it here.
Related reading
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