Am I the only one who thinks that the legal tests in clinical negligence are sometimes harder to understand than they should be ?

The case law on my favourite topic – Bolam and other tests for breach of duty – is littered with confusion. And it strikes me that Material Contribution is too.

The But For test is, thankfully, beautifully simple and easy to understand. But what if your experts can’t tell whether the outcome would probably have been avoided or the same and you have to use the causation test of Material Contribution ?

The case of Davies v Frimley Health NHSFT 2021 EWHC 169 QB earlier this year is a recent example of the Court addressing both tests on causation in clinical negligence.

Mrs Davies died from bacterial meningitis. The Trust admitted a 2 hour 40 minute negligent delay in commencing IV antibiotics and only causation remained in dispute. The Claimant argued causation on both the But For test and Material Contribution.

The Judge found for the Claimant on the But For test. In addressing this test, the Judge stated – “I have to consider, if that had happened, is it more likely that Mrs Davies would have survived than died; or more likely that she would have died than survived ?”.

Is that correct ?

Firstly, the burden is on the Claimant to prove their case on the balance of probabilities. Secondly, surely it is not enough for the Claimant to prove that the chance of surviving with proper treatment is greater than the chance of dying (which appears to be what the Judge is saying)? Rather the Claimant has to prove that the chance of her surviving with proper treatment was more than 50% ie it was likely on the balance of probabilities.

However, the judgment is more interesting for what it says on Material Contribution. 

The Judge in Davies considered that -

  1. Where an injury is divisible, a defendant will only be held liable for the extent which they caused;
  2. Where an injury is indivisible, a defendant will be liable for the whole if they caused it using the But For test;
  3. If two defendants are liable for an indivisible injury, they are each liable for all of it.

However the Judge also appears to have accepted the Defendant’s argument that Material Contribution could only apply to a divisible injury; the injury in Mrs Davies’s case was her death, this was an indivisible injury (in the sense that you can’t apportion different parts or proportions of the injury between different causes) and therefore the test of Material Contribution was not available to the Claimant; the only test of causation which could apply in her case was the But For test.

Is this correct ?

Some commentators argue that the injury needs to be “divisible” for Material Contribution to apply. This stems from the Court of Appeal decision in MOD v AB and others 2010 EWCA Civ 1317 – the atomic test veterans case for personal injury – “The principle only applies where the condition or disease is divisible, so that an increased dose of the harmful agent worsens the disease”. In MOD v AB the Court is using “divisible” to mean dose related. However, I am unaware of any clinical negligence claim confirming that the injury has to be dose related to the negligent cause for Material Contribution to apply.

Confusingly, the word “divisible” is also used in other cases to mean that a specific proportion of the injury can be attributed to the negligent cause – something completely different. When used with this meaning, it can be argued (with merit in my view) that Material Contribution cannot apply to a divisible injury, because in such cases the Court can find that the negligence on the balance of probabilities caused that percentage or proportion of the Claimant’s injury and assess damages accordingly.

So in this sense of the word, Material Contribution requires an “indivisible” injury to apply.

My view is that this is clear from the judgment of Lord Toulson in Williams v Bermuda, citing  Professor Sarah Green – “It is trite law that, where possible, defendants should only be held liable for that part of the claimant’s ultimate damage to which they can be causally linked … It is equally trite that, where a defendant has been found to have caused or contributed to an indivisible injury, she will be held fully liable for it, even though there may well have been other contributing causes …”. That quote neatly sums up the essence of the law in this area.

To avoid further confusion, “divisible” as a term is best used to mean that a specific proportion of an injury can be attributed to an individual cause, and not “dose related”. 

In addition to confusion over the use of the term “divisible”, I should also point out that the cases disagree as to whether the Material Contribution test is a departure from the But For test (CA in Bailey v MoD) or is an application of it (PC in Williams v Bermuda). My own view is that it is best distinguished from the But For test, because it only applies if you can’t answer the But For test. However, it is correct that it is still a balance of probabilities test because you are still asking – did the negligent cause probably make a material contribution?

Some cases (eg Bailey v MoD) and commentaries also refer to Material Contribution applying to “Cumulative Cause” cases. Again my own view is that this doesn’t introduce any further requirement to prove that the causes are cumulative; there will be a number of causes of the injury (consecutive or concurrent – Williams v Bermuda) and nothing further is required.

So where does this all take us ?

My own approach to the Material Contribution test is as follows.

It only applies if on the evidence it is not possible to conclude that with proper management the injury would probably have been avoided or been the same – ie the But For test cannot give you the answer either way.

When it applies, a Claimant only needs to prove –

  1. There were a number of causes of the injury;
  2. One of them was the negligent cause;
  3. The effect of it was more than negligible.

And it matters not whether the causes were concurrent or consecutive. 

Once it applies, proving the effect of the negligence on an injury was more than negligible is much easier than proving its effect was to cause an injury which otherwise would have been avoided.

And whenever you are considering the test for causation, it is worth remembering other ways in which causation can fail – eg

– a claimant fails to prove measurable damage from the negligence (Tahir v Haringey HA 1998 Lloyd’s Rep Med 104);

- all a claimant can prove is that the negligence increased the risk of injury (also Tahir v Haringey HA 1998 Lloyd’s Rep Med 104);

- in a case with a number of potential causes for an injury a claimant fails to prove the operative one was probably the negligent one (Wilsher v Essex AHA 1988 AC 1074).

 Useful cases to remember, where Material Contribution has succeeded, are –

Bailey v MoD 2008 EWCA Civ 883 – pancreatitis;

Popple v Bimingham Women’s NHSFT 2012 EWCA Civ 1628 – hypoxic birth injury;

Sido John v Central Manchester NHSFT 2016 EWHC 407 QB – traumatic brain injury;

Williams v Bermuda 2016 UKPC 4 – appendicitis;

Andrews v Greater Glasgow Health Board 2019 CSOH 31 – bowel ischaemia;

Leach v North East Ambulance NHSFT 2020 EWHC 2914 QB – PTSD.

Finally, don’t be put off –

  • Material Contribution is an underused test for causation in clinical negligence;
  • It often appears to be a more complicated test than it really is;
  • When it applies it usually presents a lower hurdle for a Claimant to overcome than the But For test of causation.



Dr Simon Fox QC