Proof on the balance of probabilities: what this means in practice
An article on the burden of proof in civil litigation, which refers to judicial decision-making.
What proof on the balance of probabilities means in theory
Before asking what proof on the balance of probabilities means in practice, it is helpful to know what it means in theory.
In a family case (Re B  UKHL 35), Lord Hoffman answered that question using a mathematical analogy:
"If a legal rule requires a fact to be proved (a 'fact in issue'), a judge or jury 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."
In another family case (In re H (Minors)  AC 563 at 586), Lord Nicholls explained that it was a flexible test:
"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 stepfather 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."
To quote again from Lord Hoffman, this time in a judicial review case (Secretary of State for the Home Department v Rehman  UKHL 47):
"It would need more cogent evidence to satisfy [a judge] 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."
What is the difference between succeeding on the balance of probabilities and failing on the balance of probabilities? In one case (Miller v Minister of Pensions  2 All ER 372) Denning J said:
"If the evidence is such that the tribunal can say 'we think it more probable than not' the burden is discharged, but if the probabilities are equal it is not."
Expressing that in percentage terms, if a judge concludes that it is 50% likely that the claimant's case is right, then the claimant will lose. By contrast, if the judge concludes that it is 51% likely that the claimant's case is right then the claimant will win. One may well ask how the judge is expected to measure the probabilities of a case to 1%!
Applications for summary judgment are an interesting wrinkle on the balance of probabilities test. The court is being asked to decide whether or not the defendant has a real prospect of successfully defending the claim at trial. At trial, of course, the test to be applied is the balance of probabilities. So the true question for the court to consider at summary judgment stage is whether or not, on the material before it at this stage in the case (and thus usually without the benefit of disclosure or cross-examination), the defendant has established that there is a real (that is, a less than fanciful) prospect that he will be able to show at trial that his case is at least as probable as that of the Claimant. That is obviously not a high bar to surmount.
Therefore, although TCC judges are exhorted to examine critically jurisdictional defences raised in opposition to an application for summary judgment to enforce an adjudicator's decision, if the defence is that the adjudicator had no jurisdiction to determine the dispute because, for example, there was a pre-contract meeting at which an oral term varying a term contained in a written tender was discussed and agreed, there may be cases where it would be difficult for the judge to feel confident that there is no real prospect that at trial the defendant could show that this was at least as likely as that there was no such discussion or agreement.
Is the burden of proof regularly used to decide cases in practice?
Take the example of a typical case proceeding in the Manchester TCC. The claimant, Mr Smith, a local builder, is suing Mr and Mrs Jones, house-owners, for the unpaid balance on his final account. Mr and Mrs Jones are disputing the final account and are counter-claiming for damages for delay and for defects. The case comes on for trial and, over three days, the parties and their witnesses are extensively cross-examined. The judge forms an adverse impression of the reliability of both camps. The single joint expert is able to add very little, because by the time he has been instructed remedial works have already been completed, and the documentation is largely inconclusive. The judge is tempted to dismiss both claim and counterclaim on the basis that neither party has established its case on the balance of probabilities. Is it likely that he would do so? Although he might be tempted, he is unlikely to do so, because he is likely to have the warning words of Baroness Hale of Richmond in Re B very much in his mind.
In Re B, the trial judge had to decide whether or not a child had been abused. It was a difficult case because he found himself unable to accept any of the witnesses as reliable, and there was no independent evidence to help him. He therefore considered, in the course of an extremely detailed and conscientious judgment, that he was unable to decide on the balance of probabilities either that any abuse had happened or that it had not happened. All that he felt he could safely conclude was that there was a real possibility that abuse had occurred.
The case went to the House of Lords. In the course of her speech, Baroness Hale said this:
"My Lords, if the judiciary in this country regularly found themselves in this state of mind, our civil and family justice systems would rapidly grind to a halt. In this country we do not require documentary proof. We rely heavily on oral evidence, especially from those who were present when the alleged events took place. Day after day, up and down the country, on issues large and small, judges are making up their minds whom to believe. They are guided by many things, including the inherent probabilities, any contemporaneous documentation or records, any circumstantial evidence tending to support one account rather than the other, and their overall impression of the characters and motivations of the witnesses. The task is a difficult one. It must be performed without prejudice and preconceived ideas. But it is the task which we are paid to perform to the best of our ability.
In our legal system, if a judge finds it more likely than not that something did take place, then it is treated as having taken place. If he finds it more likely than not that it did not take place, then it is treated as not having taken place. He is not allowed to sit on the fence. He has to find for one side or the other. Sometimes the burden of proof will come to his 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 is able to make up his mind where the truth lies without needing to rely upon the burden of proof."
(Paragraphs 31 and 32, judgment.)
It follows that any judge who does not want to risk a similar admonition from the appeal court is unlikely to go down that path, tempting though it may be on occasions.
There are, however, certain cases where the burden of proof may have a part to play. I will refer to two:
Non-attendance of a material witness
This has been considered on a number of occasions, recently by Lightman J in the case of Raja v Van Hoogstraten  EWHC 2890 (Ch). This case involved civil proceedings, commenced by Mr Raja before his death and continued by his family through his estate. They alleged that Mr Van Hoogstraten had procured two of his henchmen to murder Mr Raja in order to prevent him from continuing with the civil proceedings. The case came to trial on the issue as to whether or not Mr Van Hoogstraten was indeed responsible for Mr Raja's murder. Despite extensive participation in interlocutory proceedings, Mr Van Hoogstraten elected not to attend the trial or to give evidence. Lightman J had to consider the consequences of that decision. Referring to earlier decisions of the House of Lords and the Privy Council, he concluded that although the non-attendance of a material witness did not shift the burden of proof, nonetheless in the absence of a good reason for his non-attendance, his failure to call evidence in relation to a point about which he might reasonably have been expected to give evidence might convert evidence called by the other party, so long as credible, even if slender, into sufficient proof.
It is not uncommon for a party who is not calling a material witness to fail to adduce evidence to explain why he is not calling that witness, even though there may be a perfectly good reason for not so doing, and there is obviously a risk that if no explanation is received, the judge may draw what may in fact be an unjustified inference.
The application of the burden of proof in fire cases
In fire cases (that is, claims arising out of a fire at domestic or commercial premises, usually involving insurers either as defendant to a claim under an insurance policy or as subrogated claimant), typically there are a number of possible causes for the fire, ranging from criminal conduct (arson, whether of a third party or the building owner himself), through negligence (for example a carelessly discarded cigarette) down to breach of contract without fault (defective electrical equipment supplied or serviced by the defendant). Often at trial the case becomes a competition between the claimant's fire investigator propounding cause A and the defendant's fire investigator propounding either cause B, or causes B, C, D, E (albeit usually with a declining degree of conviction). The temptation for the judge is to decide which of the competing causes is the more likely, and to give judgment accordingly. However, it has been said on a number of occasions that this is unacceptable. I refer to two examples, the first of which is not a fire case but nonetheless often referred to in such cases.
In Rhesa Shipping Co v Edmunds  1 WLR 948, the trial judge, Bingham J, was faced with two competing causes for the sinking of a ship in calm weather in the Mediterranean off the coast of Algeria. It was established that the cause of the sinking was a large hole in the hull of the ship, but the cause of the hole was very much in dispute. One theory, propounded by the owners, was that it was struck by an unidentified, moving, submerged submarine, which was never detected, never seen and which never surfaced. The other theory, propounded by the insurers, was that the hull had simply opened up through prolonged wear and tear over many years. Bingham J, having considered a mass of evidence, concluded that the wear and tear theory was virtually impossible, whereas he concluded that the submarine theory was only extremely improbable. He found, therefore, that on the balance of probabilities the cause was the unidentified submarine. He was upheld in the Court of Appeal but reversed in the House of Lords.
According to Lord Brandon, Bingham J fell into error in applying the approach propounded by Sherlock Holmes in that well known legal text "The Sign of Four", in which he reminded Dr Watson:
"How often have I said to you that, when you have eliminated the impossible, whatever remains, however improbable, must be the truth?"
Lord Brandon said:
"It is, no doubt, on the basis of this well-known but unjudicial dictum that Bingham J decided to accept the shipowners' submarine theory, even though he regarded it, for seven cogent reasons, as extremely improbable."
The House of Lords held that if the judge, as he appeared to do, regarded both competing causes as improbable, then it was perfectly appropriate for him to hold that the claimant had failed to establish his case on the balance of probabilities.
In Fosse Motor Engineers v Conde Nast  EWHC 2037 (TCC), there were 5 possible causes of the fire, and Akenhead J described the case as having some features of a "whodunit" and certainly what "done it". He said:
"What is not acceptable, at the very least in a case like the current one, is to identify that there are, say, (as here) five possible causes, rank them each in percentage terms as possibilities and then select the possibility with the highest percentage as the probable cause. The only circumstances in which it would be legitimate would be if the highest ranked cause was the one which on all the evidence the judge was satisfied was the probable cause of the incident or loss in question…I consider that it is dangerous and generally a fruitless occupation to seek to rank possibilities or probabilities in percentage terms in any event. If there are five possibilities of which four are remote or extremely improbable, that conclusion may go to support a judge's finding that the remaining 'possibility' is in fact the probable cause or explanation for the event in question."
It is different when there are only two competing theories, neither of which is improbable. In Ide v ATB Sales  EWCA Civ 424, a case which reached the Court of Appeal, Thomas LJ said this:
"As a matter of common sense it will usually be safe for a judge to conclude, where there are two competing theories before him neither of which is improbable, that having rejected one it is logical to accept the other as being the cause on the balance of probabilities. It was accepted in the course of argument on behalf of the appellant that, as a matter of principle, if there were only three possible causes of an event, then it was permissible for a judge to approach the matter by analysing each of those causes. If he ranked those causes in terms of probability and concluded that one was more probable than the others, then, provided those were the only three possible causes, he was entitled to conclude that the one he considered most probable, was the probable cause of the event provided it was not improbable."
This paper was first given at the TeCSA/TECBAR Conference 22 October 2009 and is published with the kind permission of HHJ Stephen Davies.