Experts warn Letby inquiry of misreading stats to explain 'suspicious' deaths
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Re: Experts warn Letby inquiry of misreading stats to explain 'suspicious' deaths
#2Anybody who closely followed this case who could identify for the readers here any direct evidence of these crimes, or should we read this article to imply Lucy herself might be innocent?
Re: Experts warn Letby inquiry of misreading stats to explain 'suspicious' deaths
#3Quite right. I remember Ben Goldacre's book Bad Science documenting a few examples. I hope these are the same examples raised in the letter, because otherwise a lot of miscarriage of justice has happened in the UK.
What I remember from the book is entirely innocent people jailed because the wrong statistical question was asked. IIRC along the lines of two deaths, and the question asked was what is the chance of this happening? As opposed to, assuming the first death, what is the chance of the second? As opposed to, assuming two deaths, what is the chance of bad luck versus malice.
(I am not commenting on the Letby case per se. AIUI there is an appeal pending and UK law can be rather strict. Simply, we should not respond to possible horrible events by convicting other people who are innocent of statistical flukes, or misrepresented statistics.)
Re: Experts warn Letby inquiry of misreading stats to explain 'suspicious' deaths
#4Anybody who closely followed this case who could identify for the readers here any direct evidence of these crimes, or should we read this article to imply Lucy herself might be innocent?
The evidence suggests that many of the deaths had symptoms consistent with being injected with air. We would need to have a model of P(symptoms_i|not injected with air) to try and get to the possibility of there having been a miscarriage of justice.
Re: Experts warn Letby inquiry of misreading stats to explain 'suspicious' deaths
#5> There are obvious parallels with the Lethby case. Statements in de Berk’s diary about ‘a very great secret’ and a ‘compulsion’ on a day that a patient had died were given a sinister interpretation.
They didn't include any examples of the parallel. This goes over some of the notes:
https://www.theguardian.com/uk-news/2022/oct/13/lucy-letby-p...
> On another, she wrote “I am a horrible evil person” and on another in capital letters: “I AM EVIL I DID THIS,” the jury was told.
> She also wrote on the note: “There are no words”, “I can’t breathe”, “kill myself”, “I haven’t done anything wrong”, “how can I get through it?” and “I am an awful person”. She had also written “No Hope” and “Panic Fear” and then circled in capital letters “HATE”.
Personally, I don't think any of this is strong evidence, since she contradicts herself a bit. But the notes more directly address the murders because she wrote them in response to the accusations. It isn't as vague as a diary entry mentioning a secret.
And as far as I know, they had more evidence in the form of testimony from experts suggesting the babies were killed by injecting them with air, but I'm sure there are reasons to be skeptical of that.
Mainly, I don't know how strongly any statistical "evidence" was presented in court, how much the jury depended on it in their guilty verdict, and how the UK court system works, so I don't have a strong opinion. But I also don't believe a not-guilty person would think to write anything like what she wrote in those notes.
One last thing I'm curious about and have never heard definitive information on is whether babies stopped dying when they took Letby out of the NICU or whatever they call it. I suppose that might still be accounted for in this statistical coincidence element the RSS and other statisticians are discussing.
Re: Experts warn Letby inquiry of misreading stats to explain 'suspicious' deaths
#6Quite right. I remember Ben Goldacre's book Bad Science documenting a few examples. I hope these are the same examples raised in the letter, because otherwise a lot of miscarriage of justice has happened in the UK. What I remember from the book is entirely innocent people jailed because the wrong statistical question was asked. IIRC along the lines of two deaths, and the question asked was what is the chance of this…
Just for clarity: statistics were not used in the Letby prosecution.
The problem with Letby is that a serial killer was able to hide because finding a rare event (a member of staff murdering multiple babies) is hard to do in the noise (the mish mash of data available).
Currently the English NHS is moving away from SIRI (Serious Incident Requiring Investigation) to PSIRF (Patient Safety Incident Response Framework) which focuses a lot more on "no blame" and "open culture", so it's important that NHS Trusts get the stats right to be able to detect and understand these very rare events.
Re: Experts warn Letby inquiry of misreading stats to explain 'suspicious' deaths
#7Anybody who closely followed this case who could identify for the readers here any direct evidence of these crimes, or should we read this article to imply Lucy herself might be innocent?
> or should we read this article to imply Lucy herself might be innocent?
No, the point being made is that a murderer was able to evade detection because her employing organisation did not understand the data they had, because they did not understand statistics.
Re: Experts warn Letby inquiry of misreading stats to explain 'suspicious' deaths
#8The expert statistical analysis alluded to is simply the framework for causal inference. Had Letby not been on duty for a similar group of patients, would the number of patients who had died been the same?
If the answer is no, then a follow on question regarding whether or not factors associated with Letby could have resulted in the deaths rather than Letby herself. This could be a fellow worker who always worked in tandem with her etc.
Finding the appropriate set of data and applying statistical techniques for this is not trivial hence the expert mention.
Re: Experts warn Letby inquiry of misreading stats to explain 'suspicious' deaths
#9Anybody who closely followed this case who could identify for the readers here any direct evidence of these crimes, or should we read this article to imply Lucy herself might be innocent?
She kept notes, apparently there was an abundance of evidence in her home, doctors had raised concerns.
This isn't a case of relying solely on data, rather the data bear out what everything else suggests.
Re: Experts warn Letby inquiry of misreading stats to explain 'suspicious' deaths
#10In two cases, the victim died by insulin overdose, Letby herself admitted that the only possible explanation was foul play. That means there is a killer on the ward. The police interviewed the other nurse on the shift, and she was cleared. Even if Letby gets acquitted from the other cases, her sentencing likely will not change.
One challenge for the defence was that there are few studies on injecting air in small babies for obvious reasons. Air embolisms are very painful, and such a study wouldn't pass ethics approval, let alone parental consent.