Causation - What you Should, And Should Not, Ask Your Expert

Medical Indemnity InsuranceWhen medical practitioners are sued, they understandably tend to conclude that if they have made a mistake, they are liable for any injuries the patient has suffered. However, for a patient to be successful in their claim against a medical practitioner, the law requires that they prove not only that the doctor breached his or her duty of care, but that the breach caused the loss.

Coote v Kelly : How well do we understand causation?

The recent decision of the NSW Court of Appeal in Coote v Kelly1 suggests that lawyers, like doctors, struggle with the issue of causation. As a legal concept, it can be quite obtuse, but getting it right is crucial. The background is lengthy as the litigation spanned five years, with two trials and two appeals.

The facts: On 3 September 2009, Mr Coote visited his general practitioner, Dr Steven Kelly, who diagnosed him with a plantar wart on the sole of his left foot. In early March 2011, a biopsy revealed the lesion was in fact a malignant melanoma which had metastasised.

Mr Coote sued Dr Kelly. In March 2012, the Court found that Dr Kelly had been negligent but that causation had not been established (first decision). Mr Coote died on 23 May 2012. His widow challenged the finding on causation and Dr Kelly challenged the finding on breach. Both challenges were upheld and a direction made for a new trial.

In a judgment delivered on 13 October 2016, all three proceedings2 were dismissed on the basis that no breach of duty had been established. Davies J also concluded that, had he found negligence on the part of Dr Kelly, Mrs Coote had, nevertheless, failed to establish causation (second decision). Mrs Coote appealed the findings on both breach and causation.

The decision: The appeal was dismissed.

The case centred on the competing evidence of Mr and Mrs Coote on the one hand, and the medical practitioners (including Dr Kelly) on the other. Mrs Coote’s evidence was that before her husband’s first consultation with Dr Kelly, the lesion on his foot was pigmented. The evidence of Dr Kelly and the other doctors who saw Mr Coote was that there was no pigmentation. This evidence was relevant to both breach – the diagnosis of a plantar wart would be unsustainable if the lesion was pigmented – and causation – if the lesion was pigmented that fact could be used as evidence in determining when it metastasised.

The case was run on the basis that the melanoma needed to be removed before it metastasised. The trial judge had not been satisfied that, had there been a melanoma in late 2009, it had not already metastasised by the last time Dr Kelly saw him in August 2011.

What is so interesting about Coote v Kelly?

Coote is essential reading for lawyers who engage experts for opinions on breach and causation. When framing questions for experts, it is important that the questions are clearly defined, concise and consistent. Posing a question which has a hypothetical – and ultimately disproven – factual assumption is potentially dangerous, cumbersome and expensive.

In Coote, the expert witnesses were asked to form a conclave, and so the questions put to them were drafted jointly by the parties’ solicitors. The Court was critical of the questions as they referred “somewhat indiscriminately, to “metastasis”, “metastatic spread or distribution”, “metastatic spread to distant organs” and… somewhat randomly to possibilities, probabilities and events.”3

The first question asked was whether it was possible to say that the lesion was metastatic at the various dates Mr Coote was seen by Dr Kelly. The Court was critical of this question for two reasons:

Scope of question: There was conflicting evidence as to what the lesion was at the relevant times.4 Therefore, the question should have been “was this a melanoma?” and not “was it metastatic?” The experts should have been asked whether the lesion was, on balance, a melanoma at the relevant times. If the answer was “no”, then the issue of causation goes away.

Test for causation: The standard of proof for causation is probability, not possibility.5 If the answer to the first question (above) was “yes”, the next question should have been “on the balance of probabilities, had the melanoma metastasised as at that date?” If the answer was “yes”, then causation is established. Kiefel J (as she then was) says in Tabet v Gett “the common law treats what is shown to have occurred as certain.”6

As framed, the questions overly complicated the exercise and set up a hypothetical framework for the determination of causation which Basten JA considered inappropriate, saying “[t]here was some degree of awkwardness in asking whether a melanoma, which had not been shown to probably exist in that period, had been shown probably not to have metastasised.”7

Would it have made any difference?

One might ask, does it really matter? In short, yes. The outcome may have been different if the questions had been separated out into logical stages as above.

The experts were divided as to whether the lesion was a melanoma at the relevant time (Mr Coote’s experts said yes, Dr Kelly’s said no). If this specific question had been put to the conclave, after some discussion they may have agreed that the lesion was a melanoma at the relevant time. That would not have been a stretch given they were evenly split and the Court of Appeal considered the judge’s finding (that the lesion was not a melanoma at the relevant time) to be “controversial.” Had the experts so agreed, the Court of Appeal considered that some of the evidence in respect of causation would arguably have been given different weight and “would support an inference that as at August 2009 to May 2010 it was probable that the melanoma had not metastasised.”

The above exercise is of course artificial,8 but it demonstrates that drafting clear, sequential and factually sound questions has the potential to tip the evidence in your favour, and that just might mean the difference between winning and losing.

Sophie Pennington

M: 0405 807 135


  1. Coote v Kelly; Northam v Kelly [2017] NSWCA 192
  2. Which included the widow’s claim for mental anguish and statutory claim for compensation.
  3. Paragraph 129.
  4. While the melanoma had to have always been a melanoma, there was a question as to whether Mr Coote also had a plantar wart or whether the melanoma was of a type which looked similar in appearance to a plantar wart.
  5. Kiefel J said in Tabet v Gett [2010] HCA 12 that “resort to the language of “chance” cannot displace the analysis necessary for the determination of the issue of causation… …Expressing what is said to be the loss or damage as a “chance” of a better outcome recognises that what is involved are mere possibilities and that the general standard of proof cannot be met.”5
  6. [2010] HCA 12 at paragraph 112.
  7. Paragraph 130.
  8. As acknowledged by Basten JA, paragraph 133. It is also artificial when breach had not been established.

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