Balance of Probabilities Explained
The Balance of Probabilities Test in the UK (GMC and MPTS Cases)
What is ‘the balance of probabilities’ test? In simple form, the test might be summarised as this: which version of events, as advanced by the parties, or which can be drawn from inferences within the case, is more likely to have occurred than not?
Tribunals and judges must form a judgment on the balance of probabilities as to which facts they accept and which they do not, before going on to find for one party or another. Is that a straightforward explanation?
It has led to a number of cases over the years, and those precedents (decisions of the higher courts) have sought to define what it means. Here are some excerpts from law reports that help to shine some light of the definition:
In Secretary of State for the Home Department v. Rehman  UKHL 47 , Hoffman L, opined:
“It would need more cogent evidence to satisfy [a judge or tribunal1] that the creature seen walking in Regent’s Park was more likely than not to have been a lioness than to be satisfied to the same standard of probability that it was an Alsatian. In this basis, cogent evidence is generally required to satisfy a civil tribunal that a person has been fraudulent or behaved in some other reprehensible manner. But the question is always whether the tribunal thinks it more probable than not.”
*1 the original word was ‘one’.
He referred in that case to: In re H (Sexual Abuse: Standard of Proof) (Minors)  AC 563, which in turn referred to: Re B (Children), Re  UKHL 35. In that case, Hoffman L, stated (at para 2):
“If a legal rule requires a fact to be proved (a “fact in issue”), a judge or jury [or tribunal2] must decide whether or not it happened. There is no room for a finding that it might have 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 tribunal 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.”
*2 inserted for clarity in relation to MPTS hearings
See also, In re H (Minors)(Sexual Abuse: Standard of Proof)  AC 563, 586D-H, Lord Nicholls of Birkenhead stated (at para 73 of the linked version):
“The balance of probability standard means that a court is satisfied an event occurred if the court considers that, on the evidence, the occurrence of the event was more likely than not. When assessing the probabilities the court will have in mind as a factor, to whatever extent is appropriate in the particular case, that the more serious the allegation the less likely it is that the event occurred and, hence, the stronger should be the evidence before the court concludes that the allegation is established on the balance of probability. Fraud is usually less likely than negligence. Deliberate physical injury is usually less likely than accidental physical injury. A step-father is usually less likely to have repeatedly raped and had non-consensual oral sex with his under age stepdaughter than on some occasion to have lost his temper and slapped her. Built into the preponderance of probability standard is a generous degree of flexibility in respect of the seriousness of the allegation.
Although the result is much the same, this does not mean that where a serious allegation is in issue the standard of proof required is higher. It means only that the inherent probability or improbability of an event is itself a matter to be taken into account when weighing the probabilities and deciding whether, on balance, the event occurred. The more improbable the event, the stronger must be the evidence that it did occur before, on the balance of probability, its occurrence will be established.”
It was clarified in Re B (above) that this does not mean a higher standard of proof, such as the criminal standard, or a higher standard of proof than the civil standard. It merely means that inherent probabilities should be considered when assessing the evidence on the balance of probabilities, such as the lioness versus an Alsatian dog walking in a park. Which one is more probable, and what element of evidence is needed to analyse those probabilities. Cogency of evidence might be needed but not by diluting the simple balance of probabilities test to be some hybrid test.
In Re B (at para 14):
“14. Finally, I should say something about the notion of inherent probabilities. Lord Nicholls said, in the passage I have already quoted, that —
“the court will have in mind as a factor, to whatever extent is appropriate in the particular case, that the more serious the allegation the less likely it is that the event occurred and, hence, the stronger should be the evidence before the court concludes that the allegation is established on the balance of probability.”
15. I wish to lay some stress upon the words I have italicised. Lord Nicholls was not laying down any rule of law. There is only one rule of law, namely that the occurrence of the fact in issue must be proved to have been more probable than not. Common sense, not law, requires that in deciding this question, regard should be had, to whatever extent appropriate, to inherent probabilities. If a child alleges sexual abuse by a parent, it is common sense to start with the assumption that most parents do not abuse their children. But this assumption may be swiftly dispelled by other compelling evidence of the relationship between parent and child or parent and other children. It would be absurd to suggest that the tribunal must in all cases assume that serious conduct is unlikely to have occurred. In many cases, the other evidence will show that it was all too likely. If, for example, it is clear that a child was assaulted by one or other of two people, it would make no sense to start one’s reasoning by saying that assaulting children is a serious matter and therefore neither of them is likely to have done so. The fact is that one of them did and the question for the tribunal is simply whether it is more probable that one rather than the other was the perpetrator.”
These are just some of the cases on the definition and scope of the concept of the balance of probabilities. The GMC still has the burden of proof to prove the case against a doctor, which means that the doctor does not have to prove anything. It is for the GMC to prove each of the facts in the allegations. However, it will greatly assist a doctor’s case if they can advance through evidence matters that support their version of events and matters that undermine the case advanced by the GMC.
Does Applying the Balance of Probabilities Test Arrive at the Truth?
In Towuaghantse v General Medical Council (Rev 2)  EWHC 681 (Admin) the appeal court opined (at para 74) that:
It is perfectly normal in a forensic process, where there are two versions of events, for one version to be preferred by the fact-finder (on the balance of probability) but without a consequential condemnation of the exponent of the other version as a liar. This unsententious approach reflects a judicial self-awareness of our fallibility as fact-finders, as Baroness Hale of Richmond recognised in Re B (Children) (Care Proceedings: Standard of Proof)  UKHL 35,  AC 11 at  where she said:
“…the “risk” is not an actual risk to the child but a risk that the judge has got it wrong. We are all fallible human beings, very capable of getting things wrong.”
“…the disconcerting truth is that, as judges, we can never actually know what happened: we were not there when whatever happened did happen. We can only do our best on the balance of probabilities …” (original emphasis)
In essence, the tribunal or court arrives at a conclusion it considers to be more probable to have occurred than not. That, in itself, demonstrates that while the process will be deemed a fair one, if the rules of evidence are properly applied, the court or tribunal will not necessarily arrive at the “truth” as seen from the doctor’s perspective. But that does not mean that the decision-making process was defective.
Assessing the Credibility of Witnesses (when applying the balance of probabilities); No Requirement for Corroborating Evidence
In Byrne v General Medical Council  EWHC 2237 (Admin), the appeal judge opined, at paras  to :
“(2) The credibility of witnesses and corroborating evidence
17. First, the credibility of witnesses must take account of the unreliability of memory and should be considered and tested by reference to objective facts, and in particular as shown in contemporaneous documents. Where possible, factual findings should be based on objective facts as shown by contemporaneous documents: Dutta §§39 to 42 citing, in particular, Gestmin and Lachaux.
18. Secondly, nevertheless, in assessing the reliability and credibility of witnesses, whilst there are different schools of thought, I consider that, if relevant, demeanour might in an appropriate case be a significant factor and the lower court is best placed to assess demeanour: Despite the doubts expressed in Dutta §42 and Khan §110, the balance of authority supports this view: Gupta §18 and Southall at §59.
19. Thirdly, corroborating documentary evidence is not always required or indeed available. There may not be much or any such documentary evidence. In a case where the evidence consists of conflicting oral accounts, the court may properly place substantial reliance upon the oral evidence of the complainant (in preference to that of the defendant/appellant): Chycat §23. There is no rule that corroboration of a patient complainant’s evidence is required: see Muscat §83 and Mubarak §20.
20. Fourthly, in a case where the complainant provides an oral account, and there is a flat denial from the other person concerned, and little or no independent evidence, it is commonplace for there to be inconsistency and confusion in some of the detail. Nevertheless the task of the court below is to consider whether the core allegations are true: Mubarak at §20.”
The same appeal court also addressed the law on the standard of proof in GMC/MPT cases:
(4) “Serious cases”: the standard of proof and “heightened scrutiny”
22. The standard of proof to be applied by the Tribunal and by this Court is the civil standard of balance of probabilities. As regards the position where the allegations, or the consequences for the person concerned, are particularly serious, the Appellant referred me to Casey at §16, suggesting that there is a need for a “heightened examination of the evidence”. It was common ground that the correct approach is as set out in my judgment in O v Secretary of State for Education at §66. In that case, after referring to the relevant House of Lords and Supreme Court authorities (Re B and Re S-B) (which in turn referred to Re Doherty cited in Casey), I summarised the position as follows:
“(1) There is only one civil standard of proof in all civil cases, and that is proof that the fact in issue more probably occurred than not.
(2) There is no heightened civil standard of proof in particular classes of case. In particular, it is not correct that the more serious the nature of the allegation made, the higher the standard of proof required.
(3) The inherent probability or improbability of an event is a matter which can be taken into account when weighing the probabilities and in deciding whether the event occurred. Where an event is inherently improbable, it may take better evidence to persuade the judge that it has happened. This goes to the quality of evidence.
(4) However it does not follow, as a rule of law, that the more serious the allegation, the less likely it is to have occurred. So whilst the court may take account of inherent probabilities, there is no logical or necessary connection between seriousness and probability. Thus, it is not the case that “the more serious the allegation the more cogent the evidence need to prove it”.
(10 August 2021)
Doctors Defence Service advises on the law of evidence and procedure and law of the balance of probabilities in GMC and MPTS cases. For more information, contact us without obligation and in strict confidence on: 0800 10 88 739