Fact-finding and probability: the importance of asking the right questions

Re D (A Child)   [2014] EWHC 121 (Fam)  (Mostyn J)


This decision in a fact-finding hearing relating to children merits note here because of the helpful summary of the relevant legal principles, which are – I suggest – directly applicable to fact-finding hearings in proceedings in the CoP where it is alleged that a third party has caused harm to P.

The question that Mostyn J had to decide (as the first stage in care proceedings brought by a local authority) was whether the mother of a young child who had spent her entire life in hospital had deliberately switched off her oxygen supply.   It was common ground that there was a closed class of possible scenarios: (1) the oxygen supply was not in fact turned off, and the nurse who asserted that it was was mistaken in believing that it was; or (2) the oxygen supply was accidentally turned off by a student nurse, J; or (3) the oxygen supply was deliberately turned off by the mother.

At paragraph 31, Mostyn J set out the applicable legal principles thus:

i)            The local authority must prove its allegations on the balance of probabilities, no more, no less: Re B (Care Proceedings: Standard of Proof), [2009] 1 AC 11, [2008] 3 WLR 1, [2008] 2 FLR 141, at paras [2] and [70].

ii) 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.

iii) The more serious or improbable the allegation the greater the need for evidential ‘cogency’: Re Dellow’s Will Trusts; Lloyd’s Bank v Institute of Cancer Research [1964] 1 WLR 451 at 455; Re H (Minors) (Sexual Abuse: Standard of Proof) [1996] AC 563, [1996] 2 WLR 8, [1996] 1 FLR 80; Re S-B (Children) (Care Proceedings: Standard of Proof), [2010] 1 AC 678, [2010] 2 WLR 238, [2010] 1 FLR 1161 at para [13]. Evidential cogency is obviously needed where the harmful event is itself disputed. However, where there is no dispute that it happened the improbability of the event is irrelevant: Re B (Care Proceedings: Standard of Proof), at paras [72] and [73].

iv) Sometimes the burden of proof will come to the judge’s rescue: the party with the burden of showing that something took place will not have satisfied him that it did. But generally speaking a judge ought to be able to make up his mind where the truth lies without needing to rely upon the burden of proof: Re B (Care Proceedings: Standard of Proof) at paras [2] and [32]; Rhesa Shipping Co SA v Edmond and Another: The Popi M  [1985] 1 WLR 948.

v) It is impermissible for a judge to conclude in the case of a series of improbable causes that the least improbable or least unlikely is nonetheless the cause of the event: Rhesa Shipping Co SA v Edmond and Another: The Popi M; Ide v ATB Sales Ltd; Lexus Financial Services t/a Toyota Financial Services (UK) plc v Russell [2008] EWCA Civ 424 at para [4].

vi) There is no pseudo-burden or obligation cast on the respondents to come up with alternative explanations: Lancashire County Council v D and E [2010] 2 FLR 196 at paras [36] and [37]; Re C and D (Photographs of Injuries) [2011] 1 FLR 990, at para [203].

vii) The assessment of credibility generally involves wider problems than mere ‘demeanour’ which is mostly concerned with whether the witness appears to be telling the truth as he now believes it to be. With every day that passes the memory becomes fainter and the imagination becomes more active. The human capacity for honestly believing something which bears no relation to what actually happened is unlimited. Therefore, contemporary documents are always of the utmost importance: Onassis and Calogeropoulos v Vergottis [1968] 2 Lloyd’s Rep 403, per Lord Pearce; A County Council v M and F [2011] EWHC 1804 (Fam) [2012] 2 FLR 939 at paras [29] and [30].”

This case was not one of the “pool of possible perpetrators” class of case governed by the principles in Re S-B (Children) (Care Proceedings: Standard of Proof). In such a case the harmful act is a certainty and there is a pool of at least two guilty perpetrators.  Rather, Mostyn J found that the most that could be said against the student nurse was that she was negligent.

In an exercise of particular interest to those who care about the proper application of statistics to legal proceedings, Mostyn J then went on to analyse the three possible scenarios.  He found that he was satisfied – just – that the oxygen supply was turned off, but he resisted the submission made on behalf of the local authority that it was appropriate to proceed in stages and then to consider whether it was either (1) the student nurse; or (2) the mother who had turned it off.   A staged approach, in essence, turned something that was only just established on the balance of probabilities at the first stage into a certainty and then led to a false choice between the mother and the nurse as responsible.  For reasons the interested reader can read in more detail in his judgment, this led to the mathematically impossible situation where the relevant probabilities of the competing scenarios added up to more than 1.  Or, “[p]ut another way, a way which is less numeric and more linguistic, if there is an alleged primary harmful act and a whodunit between two possible perpetrators then in deciding the whodunit the possibility that the primary act was not in fact harmful has to be taken into account” (paragraph 39).

Mostyn J therefore was able to conclude that, on the balance of probabilities, if the supply was turned off the mother did not do it.  But it did not flow from that – he emphasised – that he was concluding that the student nurse, J, turned off the supply by accident.  Rather, a correct application of the laws of probability led him to conclude that he was not satisfied on the balance of probability that she turned off the supply either.


The application of the laws of probability by Mostyn J is the subject of an extremely interesting discussion by Ian Hunt, an independent statistician, in a paper here.

Whilst I am very alive to the fact that there are clear distinctions in principle between proceedings in the CoP and those relating to children, I have had cause in the past to note the forensic similarities between certain of the exercises that are required in both sets of proceedings (see, for a recent example, the discussion in relation to disclosure in the case of RC and the comments of McFarlane J as he then was in Re SA [2010] EWHC 196 (Admin), [2009] COPLR Con Vol 362).  I therefore have no hesitation in suggesting that the principles distilled by Mostyn J are equally applicable to ‘safeguarding’ cases before the CoP.   They also – by the same token – stand as a reminder of the need for real forensic clarity on the part of all those involved in fact-finding.

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