Why it matters in the Letby case
Named statisticians have argued the public framing of the Letby shift chart invited the same kind of inferential error the Court of Appeal warned against in Clark.
Statistical explainer
The prosecutor's fallacy
The prosecutor's fallacy is the error of confusing the probability of evidence given innocence with the probability of innocence given evidence. It was central to the Sally Clark statistical-evidence miscarriage of justice (1999 conviction quashed 2003).
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Prosecution position
The public and courtroom framing of the shift chart invited the inference that a pattern this striking could not have arisen innocently.
Expert challenge / post-conviction reading
Named statisticians argue this is the prosecutor's fallacy — treating the probability of the evidence given innocence as if it were the probability of innocence given the evidence. The Court of Appeal warned against exactly this in quashing Sally Clark's conviction in 2003.
What remains uncertain
Whether the jury reasoned in this way is not knowable. The critique is about how the material was framed and what inference it invited, not about what any juror concluded.
Common questions
What is the prosecutor's fallacy?
Confusing two different probabilities: how likely the evidence is if the defendant is innocent, and how likely innocence is given the evidence. They are not the same number, and treating them as one overstates the case.
Where was it decisive before?
In R v Sally Clark. She was convicted in 1999 partly on statistical evidence the Court of Appeal later found had been unsafely presented; the conviction was quashed in 2003.
How does it apply here?
Critics argue the shift chart's framing invited the same inversion — from 'how unlikely is this pattern by chance' to 'how unlikely is innocence'.
Did the trial judge address it?
See the linked pages for what the trial record and the summing-up contain. The site sets out the record rather than characterising it.
Related reading
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