Context
Sir David Spiegelhalter, Emeritus Professor of Statistics at Cambridge and past president of the Royal Statistical Society, has made sustained public commentary on the Letby statistical evidence across broadcast interviews, newspaper articles and academic-forum contributions from 2023 onwards. As the UK’s most widely recognised statistical-communicator voice, his commentary has cut through to audiences that specialist academic work does not reach.
The Spiegelhalter framework in outline
- Make the denominator explicit. A pattern is only informative against the denominator it is drawn from. Implicit denominators produce selection-effect problems.
- Distinguish probability of evidence from probability of guilt. The prosecutor’s fallacy confuses P(evidence | innocent) with P(guilty | evidence).
- Model competing hypotheses. A statistical analysis that models only the prosecution hypothesis cannot discriminate between it and the alternatives.
How the Letby chart fails each principle
- The shift-rota chart’s denominator of non-selected events was implicit.
- The probability of shift-overlap given innocence was treated as probability of guilt given shift-overlap.
- The natural-cause and systems-failure alternatives were not formally modelled.
The statistical-communication dimension
Spiegelhalter’s particular contribution is pedagogical: he makes the statistical critique accessible to non-specialists. For a CCRC review, the Court of Appeal, and the wider public audience, his framework is the bridge between specialist statistical argument and lay comprehension. The specialist critique is the same critique Gill, Green, Hutton and Fenton have developed; Spiegelhalter’s framing communicates it.
Read alongside
Sir David Spiegelhalter — biography, The Bayesian framework, The Sally Clark parallel, Statistics deep-dive.