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Mostyn-tacious – a judgment that makes your temples throb

 The case of Re D (A child) 2014 presented Mostyn J with a very very serious issue to try.

 The child, D, was profoundly unwell, with a great deal of problems.

 A very full report by a consultant paediatrician, indicates that D suffers, or is suspected to suffer, from, inter alia, sublugotic stenosis, chronic lung disease, cerebral palsy, visual impairment, epilepsy, sickle cell disease inherited from her parents, aspiration pneumonia, and gastroesophageal reflux. As a result she has suffered multiple cardio-respiratory arrests, is fed naso-gastrically and has undergone both insertion of a central line and a tracheostomy through which she is continuously administered oxygen – she is oxygen dependant. She will require 24 hour intensive care even upon discharge from hospital.

 On 2nd July 2013, there was a suspicion that D’s mother had deliberately turned off the tap which controlled the oxygen supply to D.

 There ended up being three, and only three possibilities


  1. The tap had not been turned off, and the medical staff who believed that it had were wrong
  2. The tap had been turned off, but it had been done so accidentally by a student nurse J
  3. The tap had been turned off deliberately by the mother



It is fairly easy to see that if a student nurse had made such a dreadful mistake, that would have some consequences. Likewise, if the Court were to find that mother had done so deliberately that would have very serious consequences for her.  Therefore, if the medical staff who believed the tap had been turned on were wrong, that would be important to know.


The police had undertaken a forensic exercise, but the only DNA on the tap was D’s herself. Obviously D was not capable of touching the tap, so the DNA would have been transferred there by another person touching the tap. So, the forensic evidence did not really help one way or another.


Here’s where things start to get complicated. Obviously, before you move to the identification of a perpetrator  (the whodunit exercise), you first want to establish whether anyone did anything.


Mostyn J indicated that he was satisfied that it was more likely than not that the tap HAD been turned off.


As he then pointed out, once he had found that it was more likely than not, the binary approach turns that into a probability of 100%.  Once a Judge finds that X event was more likely than not to have happened, then it happened.


The law operates a binary system in which the only values are 0 and 1. The fact either happened or it did not. If the court is left in doubt, the doubt is resolved by a rule that one party or the other carries the burden of proof. If the party who bears the burden of proof fails to discharge it, a value of 0 is returned and the fact is treated as not having happened. If he does discharge it, a value of 1 is returned and the fact is treated as having happened: Re B (Care Proceedings: Standard of Proof), at para [2] per Lord Hoffmann.


And moving onto the ‘whodunnit’ part, the Court no longer takes into account that there was doubt about the first element, because it is a proven fact.  [i.e once the Court has found as a fact that an injury happened, then on considering who perpetrated it there is no longer a final option of “nobody did anything”]



Mostyn J was clearly in difficulties with that. He provided some probabilities, purely by way of example.


  1. Counsel for the Local Authority asks me to consider scenario (i) first. She invites me to find first on the balance of probabilities that the oxygen supply was indeed turned off and that Nurse G is not mistaken about that. As I will explain, I accept that submission notwithstanding that I have some serious concerns that I may well be wrong. I will find on the barest balance of probability that the supply was turned off. I appreciate that in a different context in Re B (Care Proceedings: Standard of Proof) at para 44 Lady Hale stated that “it is positively unhelpful to have the sort of indication of percentages that the judge was invited to give in this case”. However I do not think that prevents me from indicating, only for the sake of example, that the probability that the supply was turned off was 55% (or as the mathematicians would say P = 0.55 and Q = 0.45). Indeed, were I not to do so I believe that a serious injustice may well arise in this and other cases, for the reasons that follow.
  1. If I approach the exercise in the staged way suggested by Counsel for the Local Authority then the 55% probability which I ascribe to scenario (i) is converted by reason of Lord Hoffmann’s binary method of judging to a 100% certainty (or P = 1). What is a mere likelihood (in the true sense of the word) is transmuted into a certainty. The 45% probability that the oxygen supply was not turned off simply will not feature in the second stage which inquires into who turned it off.



What he then says, is (and indicating that he ascribes these percentage values purely for illustration) – what if the Judge then thinks that between the two remaining probabilities  (the student nurse did it v mother did it) he ascribes a 60% chance to the student nurse and 40% to mother…


On the traditional approach, having established that someone turned off the tap (it is more likely than not that someone did, so it becomes a judicial fact), one would then just find that it was more likely than not that the student nurse did it accidentally.


But if you sit down and do some maths, as Mostyn J did


Well, you then end up with


1.         The chance that the tap was not turned off and it was a mistake                        45%

2.         The chance that the tap was turned off by the student nurse 33% [that being 60% of the 55% chance that the tap WAS turned off]


3.         The chance that the tap was turned off by the mother       22%  [that being 40% of the 55% chance that the tap WAS turned off]


[That adds up, as probabilities must, in a closed system where there are no other options, to 100%.  And the largest of those probabilities is that the tap wasn’t turned off – although none of them hit the magic 51% that would show that it was MORE LIKELY THAN NOT]


As you can see, you get two contradictory results, depending on whether you approach the three possibilities in a LINEAR way (deciding first whether the tap was turned off, and then who did it)  or whether you calculate the probabilities of each event and THEN look at which is the most likely.

What is being illustrated here, is that if, instead of a two stage process

1. Did the event happen?

2. Who did it?

One compresses that into a one stage process

1. Is it more likely than not that person x did event y ?

 You can end up with two different answers.


That led Mostyn J to form these two conclusions


 I have already indicated that on the barest balance of probabilities Nurse G was right to deduce that the oxygen supply was turned off. The grip on the tap in the off position is distinct if slight. She has been consistent in her contemporaneous statements. She is an experienced and meticulous nurse. On the other hand, she accepted that this may well have been an event where the oxygen saturation level fell even though the oxygen was on, and that she may have jumped to a conclusion. There was a great drama happening and attention to detail may have been wanting. Having considered the matter very carefully I am satisfied, just, that the supply was turned off, but I do record that my doubts are very real.


[i.e that the Court finds it was more likely than not that the tap WAS turned off, although there’s a significant possibility that it wasn’t.]


But then


Having weighed all the evidence very clearly I conclude on the balance of probabilities that if the supply was turned off the mother did not do it. In the light of Lady Hale’s strictures I do not ascribe a percentage probability to this finding but I am confident in it. But it does not follow from this finding that I am concluding that J did turn the supply off by accident. Far from it. A correct application of the laws of probability leads me to conclude that in relation to her also I am not satisfied on the balance of probability that she accidentally turned off the supply.



[Explicitly finding that IF the tap was turned off, mother did not do it, but also making clear that this does not mean that the only remaining of the three possibilities – that the student nurse, J, did it, was what the Court found. In fact, that this possibility is not found either. ]



I think (deep breath) that the finding actually ends up being (though this is never baldly stated)


Whilst it appears that it is more likely than not that the tap was turned off, once one factors in the doubt about this, it is not more likely than not that the tap was turned off EITHER by  J, the student nurse, or by the mother, and thus no findings can be safely made against either mother OR J the student nurse.



I can see what Mostyn J is getting at here, but it is clearly problematic that a Judge faced with the exercise of hearing the evidence about a very grave allegation ends up not finding that any of the only three probabilities is more likely than not to have happened.  You end up with an odd situation that the Judge basically hints that the MOST likely of the three explanations is that the tap was not turned off, even though the only thing that he found WAS more likely than not was that the tap WAS turned off.


A problem here is that the case before him didn’t easily settle into a Lancashire finding – i.e that (i) it is more likely than not that someone turned off the tap (ii) the Court can’t identify the perpetrator, but that the only two possibilities are the student nurse J and the mother and neither can be safely excluded


The reason being that the ‘motivation’ for turning off the tap is different for the two potential perpetrators – one is an accident, and one is deliberate. So a Lancashire finding doesn’t really resolve anything.  [It is, at least arguable that if the scenario had been that either mum or dad had deliberately turned off the tap and nobody else could possibly have done it, then, a Lancashire finding would have been made]



The other problem is that whilst the numbers used by Mostyn J are arbitrary, for illustrative purposes, the residual impression is that Mostyn J considered that if the tap HAD been turned off, it was much more likely to have been by the student nurse than by the mother, that being caused simply by the numbers he plugs into his calculations.


That residual impression is quite a big deal for the nurse in question, and I wonder whether the human importance of what was being deliberated here got somewhat lost in the maths.

 I wonder if these arguments are going to be imported into other cases, or whether Mostyn J is pretty much the only Judge who is going to divert from the standard way of dealing with findings.

One thing is for sure, counsel appearing before Mostyn J in finding of fact cases would do well to read up a bit on probability theory and bring a calculator (and perhaps some Migraleve).