The use of statistical evidence in clinical negligence cases

Can a claimant in a clinical negligence claim who is unable to prove the precise mechanism by which a positive outcome would have been achieved still succeed on causation? Yes, held the Court of Appeal in Schembri v Marshall[1]. The judgment also provides a useful summary of authorities dealing with the use of statistics for causation purposes in clinical negligence cases.

On 25 April 2014 Mrs Marshall visited her GP Mr Schembri complaining of chest pains. She was not referred to hospital and she died the next morning as a result of an untreated pulmonary embolism. Mr Marshall, the Deceased's husband, brought a claim for damages against Mr Schembri alleging that the Deceased should have been referred to hospital where she would have received life-saving treatment and the failure to do so caused her death. Mr Schembri admitted a breach of duty but denied causation, arguing that the deceased would likely have died even if she had been so referred.

At first instance Stewart J considered extensive expert evidence and medical literature concerning survival rates following a pulmonary embolism. The Judge found the Claimant was unable to prove that the Deceased would have been in the 64-75% who would have survived a cardiogenic shock (paragraph 115). The Claimant was further unable to prove a specific train or mechanism which, absent the admitted negligence, would have saved the Deceased.

However, Stewart J then considered a separate, overriding question: was it nevertheless more likely than not that the Deceased would have survived had she been referred to hospital? Stewart J decided that this was all the Claimant needed to prove and it was unnecessary to establish the precise mechanism by which survival would have been achieved. In considering the wealth of statistical evidence as a whole Stewart J found that the Deceased's chances of survival would have significantly increased had she been in hospital when she became unstable but made no findings as to exactly why this was the case.  The claim succeeded.

The Defendant appealed arguing inter alia that:

• Having found that the Claimant had not proven that the Deceased would have survived had she been admitted to hospital on the basis of detailed analysis of the particular circumstances the Judge should have concluded the claim must fail;
• The Judge should not have posed a separate, overriding question based on general survival rates of patients who have suffered pulmonary embolisms whilst in hospital.

The Court of Appeal reviewed the following authorities when coming to a decision:

• The Appellant relied upon Wardlaw v Farrar[2]. In that case, involving similar circumstances, the Court of Appeal cautioned against the use of general statistical evidence to challenge fact specific findings on causation. Brooke LJ held at paragraph 35 of that judgment that "While judges are of course entitled to place such weight on statistical evidence as is appropriate, they must not blind themselves to the effect of other evidence which might put a particular patient in a particular category, regardless of the general probabilities."
• The Respondent relied on Drake v Harbour[3] arguing that the Judge was entitled to draw an inference from the facts in circumstances where there had been an admitted breach of duty.
• Both parties relied on the case of Gregg v Scott[4]. At paragraphs 27-32 of Gregg Lord Nicholls acknowledged that statistical evidence is not strictly a guide to what would have happened in a particular case but at times statistical evidence will be the main evidential aid. When there is nothing better the courts should be able to use the statistical figures and give them such weight as is appropriate in the circumstances, especially when the reason why the actual outcome for the claimant patient if treated promptly is not known is due to the defendant's negligence.

Having considered the above, the Court of Appeal upheld the 'common sense and pragmatic' decision of Stewart J (paragraph 53). Having found that the specific mechanism could not be proved the Judge took a 'legitimate pause for thought' and looked at all the statistical data available. This was necessary because of the large number of unknowns and because the actual outcome was unknown due to the appellant's negligence (paragraph 51). Further, whilst it clearly suited the Appellant to rely on statistical evidence when considering whether a specific chain of events was established he could not 'sweep away such evidence' when it became inconvenient in respect of a more general question (paragraph 52).

The Court of Appeal nonetheless emphasised that statistics were not determinative of causation and each case remains fact specific (paragraph 56). This was not a case in which statistics were used to transpose a strong case in the appellant's favour into a decision in favour of the respondent. Instead Stewart J considered the Deceased's individual condition and her likely presentation at hospital and legitimately considered statistical evidence when coming to his conclusion. Defendants should not therefore be too perturbed by the decision; causation arguments may still be advanced even where the Claimant has obtained favourable statistical evidence, particularly where the facts and circumstances suggest the case outlies the statistical norm.

 

[1] [2020] EWCA Civ 358

[2] [2003] EWCA Civ 1719

[3] [2008] EWCA Civ 25

[4] [2005] 2 AC 176