What implications does the Toombes vs Mitchell case have for other healthcare professionals?BMJ 2022; 376 doi: https://doi.org/10.1136/bmj.o162 (Published 20 January 2022) Cite this as: BMJ 2022;376:o162
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Implicit misuse of statistics as harmful as explicit misuse
Roy Meadow’s explicit misuse of statistics led to miscarriage of justice in Sally Clark’s case.. In Toombes vs Mitchell case, although there was no explicit misuse of statistics, there is implicit misuse of statistics which could be eventually harmful to the society..
Firstly, there is prosecutor’s fallacy as the Judge seems to implicitly accept that the presence of Neural tube defects (NTDs) in Miss Toombes as strong evidence that the mother has not taken folic acid supplements.. In particular, the Judge has not explicitly considered the possibility that spina bifida and other NTDs, although rare, can occur even after folic acid supplements have been taken. .
The Judge seems to have been persuaded by the extremely low rates of NTDs in mothers who do take folic acid supplements. For instance, a large China-U.S. Collaborative Project published in NEJM found that in affluent areas of southern China, the incidence rate of NTDs is very low ( 0.6 in 1000 ) when mothers have taken folic acid supplements.. But this 0.006% rate is the wrong comparator to consider as it leads to prosecutors fallacy..
Given a rare event like NTD in Miss Toombes, the comparator should not be all normal babies but instead, the denominator should be all babies with NTDs irrespective of Folic acid supplementation. It is crucial to acknowledge that NTDs can occur even after Folic acid supplementation so as to avoid prosecutor’s fallacy. .
In the China-U.S. Collaborative Project, the rate of NTDs in babies born to affluent mothers not taking folic acid was statistically higher but still very low at 1 in 1000 and not dissimilar to the long term trends in Europe.. So this real world data, shows that 38% of babies with NTDs (0.6 out of the total 1. 0 + 0.6 ) were given birth by mothers who have actually taken folic acid supplements..
This rate of 38% is entirely compatible with the only two hard facts available in this case. One is the midwife’s contemporaneous documentation saying “current medication: folic acid” and the second one is the preceding GP documentation of discussion of folic acid supplements with the mother.. This substantial 38% rate of NTDs also rules out the need to invoke convoluted explanations for disregarding these two hard facts which contradict the core assertion that the mother didn’t take any folic acid supplements.(Occam’s razor)..
Secondly, there is a conjunctional fallacy when the Judge concludes that had the mother delayed conception and taken Folic acid supplements, then a healthy baby would have been the expected outcome.. The Judge alludes to the normal baby born after second pregnancy. It is conjunctional fallacy to hypothesise that the first pregnancy would have been normal just because the second baby was normal. This fallacy ignores the innumerable obstacles to conception, pregnancy associated complications, and most importantly child-birth issues unique to a 1st pregnancy. Additionally, the confounding variable of oral contraceptives (OCPs) seems to have been overlooked. OCPs were found to increase risk of NTD in some studies and OCPs were taken by the mother immediately prior to the first pregnancy. .
Furthermore, in the pivotal Hungarian trial, folic acid was very beneficial not only in terms of alleviating NTD (almost completely) but also was beneficial in significantly reducing other congenital defects.  . Nevertheless, in this pivotal study, the risk of NTD in mothers not taking folic acid was only 3 in 1000, whereas the risk of congenital anomalies other than NTD, even in mothers taking folic acid supplements, was substantially higher at 21 in 1000.. This seven times substantially higher rate of congenital anomalies other than NTD fatally undermines the judgment, which hypothesises that a delayed conception and folic acid supplementation would have automatically led to a normal healthy baby.. If one has to use a common parlance, dice don’t have memory, each roll of dice is independent and there is no guarantee of a favourable outcome with the next roll of a dice.
It would be to detrimental to the well being of the society if judicial inferences based on fallacies are allowed to undermine economical viability of preventative health services.
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Competing interests: No competing interests
The judges comments re notes seem to my contemporaries of that time to be not based on what was normal practice. The fact that any mention of folic acid advice was recorded is to be praised not criticised.
It seems strange also that the judge is swayed by memories of a conversation that took place 20 year before when we know that people recall accurately only a tiny portion of what takes place in a consultation even when reviewed on leaving the consulting room.
What we don't record seems potentially now even more important . If it is someones belief (held strongly but not necessarily true) for example that the doctor (or midwife) did not warn them re alcohol in pregnancy, pertussis jabs, covid jabs and many many other pregnancy health advice options they may be held to be at fault for any harm to mother or baby 20 plus years later. Plainly an impossible situation and it surprises many that this decision has not be appealed.
And as the BMJ has said this week why was the GP the target of this litigation but not public health , the education system national food policy etc.
Equally sad is that many young women are unaware of the need for folate supplements pre pregnancy and in the first trimester and those needing higher dose may not see a health care person until booking with a midwife by which time it may be too late
Competing interests: No competing interests