Medical professionals are rarely negligent. Often a patient who suffers an unexpectedly poor outcome from treatment by medical professionals will have no direct evidence about what occurred to cause that result. Statistically it is unlikely that the result was caused by negligence.
A submissions often made on behalf of defendants to clinical negligence actions is that the alleged negligence is so inherently unlikely that it can be rejected. The alleged negligence, so goes the submission, can be rejected as having been inherently improbable.
Mr Justice Jay considered and rejected such a submission in Jacobs v King's College Hospital NHS Foundation Trust  EWHC 121 (QB).
The Claimant contended that during the course of an operation to repair a direct inguinal hernia the surgeon failed to identify and repair an indirect inguinal hernia. The surgery was performed by a Mr El-Hasani. The Claimant was reviewed post-operatively by a nurse, Ms Starlene Grandy-Smith. This was by any standards a low value clinical negligence claim, but it reached trial in the High Court where evidence was heard over two days in January 2016.
Jay J observed at :
"This case raises a not unfamiliar judicial conundrum. On the one hand the court is confronted by evidence from health professionals who can have no specific recollection of this patient and are therefore compelled to rely on their standard practice and (on the instant facts) relatively sparse contemporaneous records. On the other hand the court has a lay witness, supported to some extent by her mother, who can give a reasonably compelling account of events, and is wholly convinced in her own mind that the first operation was a failure. The unshakeable cornerstone of the claimant's case is her belief that when she returned home from hospital on 13th June 2010 the lump was exactly the same."
The Court then addressed the "inherent improbability" submission that, in my experience, is commonly adopted by lawyers for clinical negligence defendants, and that was put forward in this case by Mr Gibson, for the defendant Trust. At  he said:
"I cannot accept Mr Gibson's suggested approach which is in some way to weigh up and assess the competing inherent probabilities, and to conclude that the combined chance of Mr El-Hasani and Ms Grandy-Smith "missing" (in their different ways) an indirect inguinal hernia must be lower than the chance of recurrence stricto sensu. This approach may well appeal to a mathematician or statistician, and there are occasions where statistics and epidemiology have a role in the judicial decision-making process, but this is not one of them. The difficulty is that there is no comparison of like with like, and no proper basis for placing any sort of figure on the chance of an experienced surgeon making a mistake of the suggested nature. However, that is not to say that the inherent probabilities cannot be viewed more generally and impressionistically, a point to which I will be coming later."
He later commented on his favourable impression of the surgeon and his impressive record of successfully performing such surgery.
Of course in the interests of promoting a modern legal system fit for the 21st century one must condemn the use of the Latin phrase "stricto sensu" when "in the strict sense" or would have conveyed the same meaning.
The Learned Judge became almost poetic when describing the judicial role when assessing the evidence of fact:
"All the evidence has to be weighed in the balance at all material times, with the judicial telescope, or microscope, constantly shifting in its power of magnification, bringing certain facts in and out of view, and then back into focus."
When carrying out that process he found that the lay and expert evidence for the defendant was "not quite rock-solid but it is sufficiently robust and well-anchored that it would require compelling and consistently reliable evidence on the claimant's side to undermine it. The claimant's evidence does not fall into that category"
So, the claim was defeated (total damages and interest would have been only £10,500) but the passage at  might usefully be borne in mind whenever the "inherent improbability" submission is deployed.