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I made another post yesterday on the argument that "that the suspicious deaths all lined up perfectly with Lucy Letby's shifts": https://news.ycombinator.com/i

I made another post yesterday on the argument that "that the suspicious deaths all lined up perfectly with Lucy Letby's shifts": https://news.ycombinator.com/item?id=37814339 https://news.ycombinator.com/item?id=37814339 Those arguments, as presented to the jury, relied entirely on a spreadsheet of the nurses' duty roster. There's an image here (on the Daily Mail website): https://i.dailymail.co.uk/1s/2023/08/18/22/74487747-12286051-image-a-10_1692394380922.jpg https://i.dailymail.co.uk/1s/2023/08/18/22/74487747-12286051... Looking at this spreadsheet the one thing that immediately jumps out to me is that this spreadsheet is not the entire data. The spreadsheet shows only the days where Lucy Letby was on shift and there was a suspicious incident (i.e. when a baby died or collapsed). It is very difficult to believe that there were no shifts were incidents occurred and Lucy Letby was not on shift, or times Lucy Letby was on shift but no incident occurred. Obviously, without that data that is not included in the spreadsheet it is impossible to draw any conclusions about Lucy Letby's correlation with the incidents she was convicted of causing. That's pretty much what the RSS letter points out, that: it is far from straightforward to draw conclusions from suspicious clusters of deaths in a hospital setting – it is a statistical challenge to distinguish event clusters that arise from criminal acts from those that arise coincidentally from other factors, even if the data in question was collected with rigour. And the data in that spreadsheet was certainly not presented with any rigour. Rather, this spreadsheet is a textbook example of cherry-picking. It only shows the data that justifies the prosecutor's claim. I have no way to know whether this was done consciously, in order to mislead, or it was merely the result of poor understand of statistics by police officers and prosecutors. I'm inclined to believe the latter was the case. In any case, _if_ the jurors were convinced by that spreadsheet of Lucy Letby's guilt, to whatever extent (weighing it in view of other evidence), then they did so without having enough information.

gus_massa 3y ago
> It is very difficult to believe that there were no shifts were incidents occurred and Lucy Letby was not on shift, or times Lucy Letby was on shift but no incident occurred. I agree. It's very strange that there was not at least one case when she was not there. Death are very clear, but it's easy to use different criteria to classify an weird case as suspicious. I'd expect more cluster of nurses. There are a few that work (almost?) in all the cases during the day, but the nights are more random. Some nurses appear only one. Which one had a full time job there and which where hired only a few times? There is a strange diagonal that starts at Child D - Nurse H. How did they sort the nurses? Alphabetically? By some internal HR number? [It may be an artifact, because people is too good detecting patterns like diagonals. I was generating a similar random grid a few years ago, and I saw too many patterns that I suspected the random generator was wrong. But it was just me overfitting the data.]
- oh_sigh 3y ago
  Infant mortality is something like 3.3 per 1000 in the UK. 25% of that happens in the first week, and women are usually discharged with their baby after 2 or 3 days. And that mortality rate includes things like known defects that are incompatible with life that would not be considered suspicious when the baby dies. So, there should be far fewer than one death per thousand of the newborns in the hospital. Since her activities took course over a year, it's quite possible that no unexplained deaths happened apart from the ones that she was involved with. It's also possible there might be one death not caused by her that just happened to occur on her shift.
  - YeGoblynQueenne 3y ago
    Note that the babies involved in the incidents were premature, and mortality for premature babies is going to be lower than that for full term babies. Further, as I understand it, those were babies that were being cared for in the Neonatal Intensive Care Unit and may have been vulnerable and less likely to survive to begin with. For example, I remember the press noting that a baby who died was no bigger than a hand. The press reported this to tug at readers' heartstrings, but it also has the effect of reminding that a baby born so early is in a precarious situation and may well not make it. In any case, the spreadsheet above doesn't give any of that information, either, so there is not enough information to know whether the deaths were suspicious in the first place. Looking at the spreadsheet, all we can say is that the only reason those incidents are associated with Lucy Letby is because Lucy Letby was on shift. Which is a tautology and not useful to make any decisions.
  - gus_massa 3y ago
    From https://en.wikipedia.org/wiki/Lucy_Letby https://en.wikipedia.org/wiki/Lucy_Letby > The numbers of unexplained collapses were particularly abnormal: there had previously been only two or three deaths a year in the neonatal unit. She was convicted for cases between June 2015 and June 2016, so I'd expect to see like 2 or 3 cases of natural deaths. Assuming she works there for 40 hours of the 168 hours of the week, it's like 1 coincidence and 1 or 2 when she was not there. Been there when 7 babies died is a LOT of bad luck. Assuming a Poisson distribution with lamba=2.5/4, P(7)=7E-13 ...

gus_massa 3y ago

> It is very difficult to believe that there were no shifts were incidents occurred and Lucy Letby was not on shift, or times Lucy Letby was on shift but no incident occurred. I agree. It's very strange that there was not at least one case when she was not there. Death are very clear, but it's easy to use different criteria to classify an weird case as suspicious. I'd expect more cluster of nurses. There are a few that work (almost?) in all the cases during the day, but the nights are more random. Some nurses appear only one. Which one had a full time job there and which where hired only a few times? There is a strange diagonal that starts at Child D - Nurse H. How did they sort the nurses? Alphabetically? By some internal HR number? [It may be an artifact, because people is too good detecting patterns like diagonals. I was generating a similar random grid a few years ago, and I saw too many patterns that I suspected the random generator was wrong. But it was just me overfitting the data.]

oh_sigh 3y ago
Infant mortality is something like 3.3 per 1000 in the UK. 25% of that happens in the first week, and women are usually discharged with their baby after 2 or 3 days. And that mortality rate includes things like known defects that are incompatible with life that would not be considered suspicious when the baby dies. So, there should be far fewer than one death per thousand of the newborns in the hospital. Since her activities took course over a year, it's quite possible that no unexplained deaths happened apart from the ones that she was involved with. It's also possible there might be one death not caused by her that just happened to occur on her shift.
- YeGoblynQueenne 3y ago
  Note that the babies involved in the incidents were premature, and mortality for premature babies is going to be lower than that for full term babies. Further, as I understand it, those were babies that were being cared for in the Neonatal Intensive Care Unit and may have been vulnerable and less likely to survive to begin with. For example, I remember the press noting that a baby who died was no bigger than a hand. The press reported this to tug at readers' heartstrings, but it also has the effect of reminding that a baby born so early is in a precarious situation and may well not make it. In any case, the spreadsheet above doesn't give any of that information, either, so there is not enough information to know whether the deaths were suspicious in the first place. Looking at the spreadsheet, all we can say is that the only reason those incidents are associated with Lucy Letby is because Lucy Letby was on shift. Which is a tautology and not useful to make any decisions.
- gus_massa 3y ago
  From https://en.wikipedia.org/wiki/Lucy_Letby https://en.wikipedia.org/wiki/Lucy_Letby > The numbers of unexplained collapses were particularly abnormal: there had previously been only two or three deaths a year in the neonatal unit. She was convicted for cases between June 2015 and June 2016, so I'd expect to see like 2 or 3 cases of natural deaths. Assuming she works there for 40 hours of the 168 hours of the week, it's like 1 coincidence and 1 or 2 when she was not there. Been there when 7 babies died is a LOT of bad luck. Assuming a Poisson distribution with lamba=2.5/4, P(7)=7E-13 ...