Why it matters in the Letby case
Critics argue the Letby investigation departed from this methodology by identifying the suspect first and constructing the event set around her presence.
Statistical explainer
Hospital cluster investigations — methodological notes
Established epidemiological methodology for hospital adverse-event clusters requires defining events independently of any suspect, controlling for unit acuity and staffing changes, and using a comparator population.
Statistical analysis2Expert/professional
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Prosecution position
The investigation proceeded from the consultants' concerns about a specific nurse to an event set and a prosecution built around her presence.
Expert challenge / post-conviction reading
Established epidemiological methodology for adverse-event clusters requires defining events independently of any suspect, controlling for unit acuity and staffing changes, and using a comparator population. Critics argue the investigation departed from that order by identifying the suspect first.
What remains uncertain
Whether a methodologically orthodox investigation would have reached a different conclusion is unknowable. The critique is that the standard method was not followed, not that following it would have exonerated anyone.
Common questions
What does the standard methodology require?
Defining the events by clinical criteria before considering who was present, controlling for changes in unit acuity and staffing, and comparing against a similar population.
What is 'suspect-first' scoping?
Starting from a person and assembling the events around them, rather than starting from the events and asking what explains them.
Have other cases shown the same pattern?
Critics point to Lucia de Berk in the Netherlands and other international serial-nurse prosecutions built on statistical artefacts. See the comparative pages linked below.
Does departing from the method prove error?
No. It means the resulting association carries less weight than an orthodox analysis would have done.
Related reading
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