Do Statistics Prove Accused Nurse Lucy Letby Innocent?
Statistical analyses, a damning 2016 report by the Royal College of Paediatrics and Child Health (RCPCH), and various other factual inconsistencies in publicly available official documents, may constitute reasonable doubt
Please forgive the personal touch but I have written this post in memory of my Mum who passed away recently and who many years ago was a nurse and midwife. I don’t know for certain that Lucy Letby did not commit the crimes of which she is accused (I don’t think she did) but, regardless, nurses everywhere should be greatly appreciated and applauded. This post is for them. And my Mum.
As readers of my blog will know, I have an interest in so-called cluster cases – criminal trials where there is an apparently high number of occurrences of some event. For example, ‘excess deaths’ at a hospital, within a family or among a GP’s patients. Or wicked postmasters fiddling books.
In such cases, particularly ones where the evidence is purely circumstantial, a grasp of statistics is critical. Since this is often lacking, whether among judges, jurors or, most worryingly, defence lawyers, there is scope for a miscarriage of justice to occur i.e. for an innocent person to be found guilty.
Where there is a cluster, it is important first to determine the probability of the cluster occurring purely by chance. In the case of ‘excess deaths’ on a particular hospital ward, this involves considering the probability of the ‘excess death’ rate occurring somewhere on that type of ward, not on one specific ward.
If it is determined that the probability is low, then the cause must be investigated. Also, such investigations can be biased – they may be conducted by those who would be implicated in some way by the true cause of the ‘excess deaths’ being determined.
The trial, currently underway in Manchester, of Lucy Letby, the neonatal nurse at The Countess of Chester Hospital (COCH) accused of murdering 7 babies and of 15 attempted murders (pertaining to 10 babies) between June 2015 and June 2016 is a cluster case, and one where the evidence is purely circumstantial.
The hospital first investigated an elevated number of deaths of very premature babies in February 2016. Almost five years later, in November 2020, Letby was charged, though at first she was charged with 8 murders and 10 attempted murders.
I should make it clear that I do not know if Letby is innocent. How could I? Nor am I going to speculate – what I present in this post are information and data gleaned from publicly available official documents, statistical analyses of said data, and references in the media to official documents, official announcements, court dialogue (all links provided).
Finally, and importantly, whether Letby is innocent or not, the parents of the babies that are the subject of the trial have gone through and continue to go through a truly terrible experience.
Below is a list of the various official sources of information and data that I refer to in this post or have read in the course of my research.
Document 1: Royal College of Paediatrics and Child Health (RCPCH) Service Review of the neonatal service at the Countess of Chester Hospital (COCH), dated November 2016 (Link 1: http://allcatsrgrey.org.uk/wp/wpfb-file/rcpch_invited_review_nov_16_final_-for_dissemination-_08_02_17_1_30pm-pdf/, Link 2: https://pdf4pro.com/cdn/www-coch-nhs-uk-7537c.pdf, Link 3: http://www.coch.nhs.uk/media/141843/rcpch_invited_review_nov_16_final_-for_dissemination-_08_02_17_1_30pm.pdf.
Note that this last link to the document on COCH’s own website now goes to a page that says, “There seems to have been an error, please navigate to the page on the menu above”).
Document 2: Care Quality Commission (CQC) Inspection Report, Countess of Chester Hospital NHS Foundation Trust, dated 17 May 2019 (Link: https://api.cqc.org.uk/public/v1/reports/75694247-129f-4e2d-8a12-b2e59d3245ca?20210116074506)
Document 3: Care Quality Commission (CQC) Inspection Report, Countess of Chester Hospital NHS Foundation Trust, dated 15 June 2022 (Link: https://api.cqc.org.uk/public/v1/reports/0257680c-6a9a-49fe-ac39-a5c982f58985?20221129062700)
Document 4: Care Quality Commission (CQC) Inspection Report, Countess of Chester Hospital NHS Foundation Trust, dated 30 September 2022 (Link: https://api.cqc.org.uk/public/v1/reports/85aed0ff-145b-4572-ab44-08bcd3124f78?20221129062700)
Document 5: Number of deaths (monthly) by type (late fetal loss, stillbirth, early neonatal, late neonatal, post neonatal) at the Countess of Chester Hospital NHS Foundation Trust, January 2013 to October 2018 (Freedom of Information Request Link: https://www.whatdotheyknow.com/request/521287/response/1255362/attach/3/FOI%204568.docx?cookie_passthrough=1)
Document 6: Mothers and Babies: Reducing Risk through Audits and Confidential Enquiries across the UK (MBRRACE-UK), Perinatal Surveillance Report, UK Perinatal Deaths for Births from January to December 2015 (Link: https://www.npeu.ox.ac.uk/assets/downloads/mbrrace-uk/reports/MBRRACE-UK-PMS-Report-2015%20FINAL%20FULL%20REPORT.pdf)
Document 7: Mothers and Babies: Reducing Risk through Audits and Confidential Enquiries across the UK (MBRRACE-UK), Perinatal Surveillance Report, UK Perinatal Deaths for Births from January to December 2016 (Link: https://www.npeu.ox.ac.uk/assets/downloads/mbrrace-uk/reports/MBRRACE-UK%20Perinatal%20Surveillance%20Full%20Report%20for%202016%20-%20June%202018.pdf )
Background/RCPCH service review (Nov 2016)
By way of background, “the Royal College of Paediatrics and Child Health (RCPCH) was invited to review the neonatal service at the Countess of Chester Hospital (COCH) following re-designation [demotion] from level 2 Local Neonatal Unit (LNU) to level 1 Special Care Unit (SCU) in July 2016 due to concerns about increasing neonatal mortality.
A number of causes had been postulated but there was no definitive explanation for the trend”. This is the opening statement in the Executive Summary of the final copy of the RCPCH report dated November 2016 (hereafter referred to as the ‘RCPCH report’).
The findings of the RCPCH report were announced to the media in February 2017, along with the report itself. Although it was the hospital itself that downgraded its own neonatal unit, the RCPCH team that visited in September 2016 found significant failings by the unit in relation to reporting, staffing, practices, etc..
The team made various recommendations that it said should be implemented before a reinstatement of the unit as an LNU should be considered.
Missing deaths
The below neonatal deaths data is taken from an official COCH document that was made public as a result of a Freedom of Information request.
Source: COCH, https://www.whatdotheyknow.com/request/521287/response/1255362/attach/3/FOI%204568.docx?cookie_passthrough=1
According to the RCPCH report, “On 8th February 2016 a half day ‘high level’ thematic review of ten of the cases took place with the involvement of the ODN clinical lead.” (RCPCH report clause 3.7)
Given that the “half day ‘high level’ thematic review” took place on 8 February 2016, it would appear that the ten cases reviewed were the ten early neonatal deaths from June 2015 to January 2016 in the above table (Table 1.1). Of these ten, Letby was later charged in relation to just three of them. In other words, she could not be connected with seven of them.
Also, she was later charged with two murders in August and October 2015 (Children E and J). But, as can be seen in the table above, there were no deaths recorded in either August or October 2015. The data in the tables above are up to October 2018, so one would assume that there was plenty of time to correct any mistakes i.e. to include the two deaths in August and October 2015.
High incidence of ‘non-malicious deaths’ (those which Letby has not been charged with)
Letby is accused of murder in relation to 7 of the deaths in 2015 and 2016, but there were 11 for which she has not been implicated (Chart 1) presumably because she could not have been responsible for them (in fact, the defence, in its opening, said that she could not have been responsible for some of the 7 deaths that she has been connected with).
If we assume that ‘non-malicious’ deaths are distributed according to the Poisson distribution (deaths are independent of each other and occur at a rate of 2.7 per year, the average of 2013, 2014 and 2017), then the odds of there being 11 deaths (the ones Letby has not been accused of) over a two year period purely by chance is 1 in 83.
In other words, the prosecution is asking the jury to believe that there is both a serial killer at work as well as some other factor (e.g. faulty equipment, understaffed unit, incompetence among medical staff) causing the deaths. And that these two factors both started and stopped at exactly the same time. Quite a coincidence!
By the way, for those who might be tempted to think the high death rate fell in 2017 (actually it was from mid 2016) because Lucy Letby was “caught”, remember that COCH’s neonatal unit was downgraded in June 2016 and so no longer was allowed to care for higher risk babies.
Chart 1
In the case of Beverley Allitt, the nurse found guilty in 1993 of murdering four infants, attempting to murder three others, and causing grievous bodily harm to a further six at Grantham and Kesteven Hospital, Lincolnshire, between February and April 1991, roster data (see below) determined (unlike in Letby’s case) that she was present at all 25 of the suspicious incidents that were investigated (Allitt was not charged for all of them).
Figure: Roster data in Beverley Allitt case
Source: The Beverley Allitt Tapes (Woodcut Media, Sky Crime documentary)
It should also be noted that Allitt never testified at her trial (according to the Greensboro News and Record, Allitt was not “in court for nine weeks of her 13-week trial because of [an] eating disorder and did not testify.
Colleagues and psychiatrists were unable to suggest a motive, and she has made no public statements” (https://greensboro.com/english-nurse-convicted-in-death-of-infant-patients/article_bec86764-b5ed-5bf1-8d5d-719e01ff22db.html).
Letby on the other hand chose to testify and spent nine days on the stand being cross examined (you can read all the reports in The Chester Standard and judge for yourself how she did). Furthermore, during the hours of police questioning, Letby did not once invoke her right to silence (again, you can read many of the various exchanges cited at trial in The Chester Standard).
This, too, is unlike Allitt, who after a certain point of police questioning refused to say anything further.
Then there is the case of nurse Colin Norris who was convicted in 2008 of murdering four elderly patients and attempting to murder two others in 2002 (his case was recently referred to the Court of Appeals following a scientific finding that hypoglycaemia can have a natural cause and in the elderly often does – according to the prosecution the hypoglycaemia in Norris’ ‘victims’ was due to him having injected them with insulin).
Norris was originally charged with five murders, but before trial roster data determined that for one of them he was not present so could not have been responsible. The police then started looking for second murderer, right?
Er, no – they just decided that a death that they were previously certain was a murder was not in fact a murder, and reduced the count to four.
High incidence of multiple pregnancies in relation to murder/attempted murder charges
“The obstetricians were confident in their ability to manage high risk pregnancies including twins and triplets to later stages of gestation, and where cots and appropriate safe staffing are available it is preferable for families to be able to stay locally following delivery.
The obstetrics team had expressed concern about four of the deaths particularly, which were discussed at the perinatal M&M meeting and found to have no antenatal indicators of concern.
The review team was however concerned at whether there were sufficient staff for the LNU to care for triplets, for example, albeit post 34 weeks.” (Clause 4.4.14, RCPCH Report)
Chart 2 below shows that the percentage of multiple pregnancies in relation to the murder/attempted murder charges was way higher than in the general population. For example, in the general population, 1.2 percent of pregnancies are multiple pregnancies.
In the case of the pregnancies at COCH where there was a murder charge, 50 percent were multiple pregnancies (three of six). In other words, it may be that the deaths and collapses reflected the high risk nature of multiple pregnancies rather than the presence of a murderer.
Chart 2
Source: https://www.itv.com/news/granada/2022-10-14/who-are-the-children-alleged-to-have-been-murdered-by-lucy-letby, https://www.raisingmultiples.org/faqs/faq-what-are-the-odds-of-having-a-multiple-birth/
Higher activity/lower admission birthweight than average
“Further in-depth analysis by the neonatal lead in July 2016 examined activity and acuity from June 2015. This included admissions per month, time between deaths, total care days per month, IT care days per month, birthweight and prematurity.
This was not a systematic review but concluded that there was higher activity and lower admission birthweight than average during the period corresponding to the increase in mortality.
This was not however considered to have been significant enough to explain the increase in mortality.” (Clause 3.8, RCPCH Report)
I would be interested to know if the term “significant” was used in its strictly statistical sense (i.e. statistical significance). I presume not, because the conclusion appears to be that of the ‘neonatal lead’, not a statistician.
Also, it appears that the higher activity/lower admission birthweight was not considered sufficiently significant because it could not solely explain the increase in mortality. Why could it not have been deemed to have been a contributing factor, one among others?
Then, what about nonlinearity? Presumably there is a point at which a small percentage increase in activity/decrease in birthweight leads to a large increase in mortality.
To what extent was this considered by the neonatal lead?
This is taken from a long document, read the rest here chimpinvestor.com
Header image: Sportskeedia
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