The Royal Statistical Society (RSS) recently convened a meeting to address concerns about the use of statistical evidence in court cases, with a particular focus on the Lucy Letby trial. Experts at the gathering expressed significant reservations about the shift pattern data presented during the trial, labeling it as "scientifically worthless."
One of the most contentious pieces of evidence in Letby's case was a chart covering a 13-month period from June 2015 to June 2016. This chart purportedly showed that Letby was present during all suspicious incidents involving infants, while her 38 colleagues were only present on a few occasions. However, statisticians at the RSS meeting argued that this data was fundamentally flawed and potentially misleading.
The experts raised several concerns about the shift pattern evidence:
- Data selection and collection issues
- Failure to consider alternative explanations
- Potential for confirmation bias
- Lack of context regarding normal hospital operations
Dr. Jane Hutton, a professor of statistics at the University of Warwick, commented on the evidence, stating, "It's a large pile of crockery, much of which is broken. Such a pile does not hold water however big it is."
The meeting also highlighted similar cases where shift pattern data led to wrongful convictions, such as those of a Dutch pediatric nurse and Italian nurse Daniela Poggiali, both of whom were later exonerated.
"If toxicology was represented you would expect a toxicologist to be present."
Statisticians at the meeting called for parity in court cases, suggesting that statistical experts should be present when such evidence is presented to juries. They emphasized the importance of providing proper context and interpretation for statistical data to prevent misunderstandings.
In 2022, the RSS produced a report titled "Health care serial killer or coincidence?" which offered guidelines for presenting data correctly in legal proceedings. The report recommended consulting independent statisticians and clearly explaining confounding factors that could distort figures. However, these recommendations were not followed in the Letby trial.
The meeting concluded with a call for greater collaboration between statisticians and legal professionals to ensure the appropriate use of statistical evidence in future court cases. While not directly challenging Letby's conviction, the experts stressed the need for a more rigorous approach to statistical evidence in criminal trials.
As of September 2024, it has been 13 months since Lucy Letby's initial conviction and 2 months since her retrial. The ongoing debate surrounding the use of statistical evidence in her case highlights the complex intersection of data analysis and criminal justice.