Why her book matters for Letby
Math on Trial (2013) is the canonical accessible reference on how statistical fallacies produce wrongful convictions. It walks through ten cases including Sally Clark and Lucia de Berk, and catalogues the specific mathematical errors that put innocent people in prison. It is the book a CCRC reviewer needs on the shelf when considering a case like Letby.
Schneps’s framework identifies several recurrent mathematical fallacies: the multiplication fallacy (Meadow’s squared-cot-death probability), the selection- effect fallacy (de Berk, Letby), the prosecutor’s fallacy (confusion of conditional probabilities), and the ecological fallacy (aggregating individual cases in ways that distort population-level reasoning).
Professional background
- Mathematician, Institut de mathématiques de Jussieu, Sorbonne Université.
- Research speciality: Galois theory, number theory, the inverse Galois problem.
- Co-author with her daughter Coralie Colmez of Math on Trial (Basic Books, 2013).
- Long-standing public-engagement work on mathematics in legal contexts, including commentary on UK and continental European miscarriage-of-justice cases.
The Schneps framework applied to Letby
Four specific Schneps fallacies apply to the Letby shift-rota chart:
- Selection-effect fallacy. Events selected as suspicious because Letby was present, then presented as evidence of her guilt.
- Prosecutor’s fallacy. P(shift overlap | innocent) treated as P(guilty | shift overlap).
- Independence fallacy. Cluster events on the same unit in the same period treated as independent events for probability calculation.
- Denominator-suppression fallacy. Numerator (events where Letby was present) shown; denominator (events where she was not, including her non-shift days) not shown.
Each of these is catalogued in Math on Trial. The Letby chart demonstrates all four.
The international-comparative dimension
Schneps’s academic work is rooted in French and American mathematical and legal contexts as well as UK. Her perspective is therefore genuinely international in the sense the Shoo Lee Panel is: not UK-specific pleading, but statistical-community consensus that crosses jurisdictions. That international-statistical-community consensus is itself evidence: a statistical framework that does not hold up across different legal systems is unlikely to hold up within any one of them.
The Math on Trial framework applied to the Letby case
Prof. Schneps is co-author (with Coralie Colmez) of Math on Trial: How Numbers Get Used and Abused in the Courtroom (Basic Books, 2013), the canonical popular-audience text on statistical miscarriages of justice. The book covers the Sally Clark, Lucia de Berk, OJ Simpson and Amanda Knox cases, documenting the specific patterns by which courtroom statistical reasoning fails when statistical methodology is applied without statistical expertise. The patterns it documents recur in the Letby shift-rota chart evidential architecture.
Prof. Schneps’s institutional position at the Institut de Mathématiques de Jussieu (Paris) gives her European-mathematics institutional standing. Her Math on Trial framework is the international public-audience-mathematics counterpart to the Royal Statistical Society’s 2022 framework: both arrive at the same evidential criteria for cluster-chart evidence in criminal trials. The convergence between UK-statistics-institutional and French-mathematics-institutional frameworks is part of the institutional weight behind the post-conviction statistical critique of the Letby evidence.
The Lucia de Berk parallel work
The Math on Trial chapter on the Lucia de Berk case sets out the structural parallel that has been most directly applied to the Letby evidential architecture: a shift-rota cluster chart used as primary evidence against a nurse defendant; selection-bias problems in event selection; the Texas sharpshooter fallacy in cluster identification; the failure of the prosecution’s statistical experts to engage with the actual baseline distribution. Prof. Schneps’s Math on Trial framework for the de Berk case is the methodological precedent for the Letby statistical critique.
Why this voice matters for the conviction-safety question
The post-conviction statistical critique of the Letby case is institutionally grounded in three distinct frameworks: the Royal Statistical Society 2022 report (Green, Hutton, Steventon — UK), the Bayesian-network approach (Fenton — UK), and the Math on Trial framework (Schneps — France). All three reach the same evidential conclusion: the Letby shift-rota chart cannot bear the evidential weight a foundational element of a criminal conviction requires. The international convergence of these frameworks is part of the post-conviction evidential picture the CCRC review engages.