In Armstrong, Carol Ann (executrix of the estate of Peter Traynor, deceased and on behalf of the dependents of Peter Traynor, deceased) v Quest Laboratories Pte Ltd and another and other appeals [2019] SGCA 75, a 5-judge Court of Appeal reversed the trial judge's finding that the negligence of a medical laboratory (Laboratory) and a pathologist, Dr T (Respondents), had caused Mr Traynor to lose four years of his life. Instead, the Court of Appeal held that but for the Respondents' negligence, Mr Traynor would have been fully cured of his metastatic melanoma, and damages should be calculated on the basis of Mr Traynor's full life expectancy.

In the highly anticipated written judgment, the Court of Appeal undertook a detailed examination of the issue of causation, and elucidated several principles which will no doubt provide useful guidance in this complex area of law. In particular, the role of statistical evidence in proving causation was thoroughly considered by the Court of Appeal.

Notably, however, the Court of Appeal did not express a view as to whether the trial judge had been correct to have recourse to the "loss of chance" doctrine or the trial judge's use of a "lost years" approach.

Brief facts

In September 2009, Mr Traynor consulted his general practitioner about an unusual mole on his back. A specimen of the mole was sent to the Laboratory for an examination and preparation of a pathology report. Dr T, a pathologist from the Laboratory, returned a pathology report indicating no malignancy.

Two years later, in December 2011, Mr Traynor discovered a lump under his right armpit. A biopsy of his axillary lymph nodes revealed metastatic melanoma. The specimen from Mr Traynor's mole taken in September 2009 was also re-examined by another pathologist, whose pathology report carried the diagnosis of "malignant melanoma with ulceration".

Despite repeated medical procedures and several rounds of chemotherapy, Mr Traynor passed away from metastatic melanoma in December 2013 at the age of 49.

The suit was brought in 2015 by Mr Traynor's widow (Appellant) as executrix of his estate and on behalf of their two daughters (as dependants).

Decision of the High Court

The trial judge held that the question of breach was straightforward in this case. Sending Mr Traynor a pathology report with a clean bill of health when the circumstances required (at the very least) further examination was, in the trial judge's view, a clear case of negligence. 

What was less clear was the issue of causation. The trial judge noted the Appellant's argument that the cancer had not spread beyond the armpits until after 2009. An earlier diagnosis would have resulted in surgical removal of the lymph nodes and arrested the spread of the cancer. As to the staging of the cancer as at 2009, which was also a contested issue, the Appellant argued that based on her experts' staging of the cancer, Mr Traynor would have had at least a 68% and closer to 80% chance of survival.

Conversely, the Respondents claimed that Mr Traynor's fate had been "biologically determined" even before the misdiagnosis. They argued that prior to September 2009, the melanoma had already distally metastasised, but remained dormant and undetectable until later on. Since the course of Mr Traynor's melanoma was already biologically determined, so to speak, the Respondents argued that they ought not to be held liable for his demise.

The trial judge was not fully persuaded by either side. While the trial judge thought that the Respondents' breach had caused Mr Traynor to "lose a fighting chance", the trial judge did not accept the Appellant's statistical evidence that Mr Traynor would have at least a 68% chance of surviving 10 years.

The trial judge took heed of Lord Nicholls' dissent in the English case of Gregg v Scott [2005] UKHL 2, where Lord Nicholls had urged courts to "leap an evidentiary gap when overall fairness plainly so requires". The trial judge's leap over the "evidentiary gap" in this case was in estimating that since Mr Traynor had survived almost four years after his misdiagnosis, he might have lived twice that number had he been properly diagnosed. Thus, the trial judge found that the Respondents' negligence had caused Mr Traynor to lose four years of his life.

On the issue of damages, there was no need for a discount rate to be applied to the multiplier-multiplicand approach in calculating the Dependency Claim and Loss of Inheritance Claim, since four years from Mr Traynor's death in 2013 corresponded with the year of the trial. As for the Loss of Appreciation Claim and the Estate Claims, these were rejected by the trial judge as they were based on the assumption that Mr Traynor would live to the age of 82.

Decision of the Court of Appeal

The Court of Appeal agreed with the trial judge's views on the Respondents' breach.

Turning to the causation question, the Court of Appeal disagreed with the trial judge's approach, and accepted the Appellant's argument that but for the Respondents' negligence, Mr Traynor's melanoma would have been cured completely. The Court of Appeal was convinced on the balance of probabilities that Mr Traynor's fate was not already "biologically determined" at the time of misdiagnosis in 2009. Furthermore, the Court of Appeal was persuaded that Mr Traynor would have availed himself of curative treatment through a sentinel lymph node biopsy which would have revealed the microscopic melanoma metastasis in the lymph nodes, followed by completion lymph node dissection. This would have completely cured Mr Traynor of his melanoma.

In coming to the conclusion that the Appellant had proven her case on the balance of probabilities, the Court of Appeal undertook a lucid and systematic examination of all of the available evidence, much of which involved medical and scientific information of a very technical nature. In so doing, the Court of Appeal observed that there was a tendency in medical negligence cases to focus overwhelmingly on the statistical evidence presented. A careful appreciation of what statistical evidence means and how it should be applied is necessary.

It followed from the Court of Appeal's findings that the Appellant's damages should be calculated on the basis of Mr Traynor's full life expectancy, and not on the basis that Mr Traynor had only lost four years of life. Within those parameters, the Court of Appeal remitted various questions on damages for the trial judge's consideration.

Key takeaways

1. Is "loss of chance" an actionable claim in medical negligence cases?

The orthodox "but for" test for causation operates on the balance of probabilities, which requires a plaintiff to show that it was more likely than not (i.e. > 50%) that the defendant's negligence caused the plaintiff's injury or damage. If this substantial hurdle is cleared, the plaintiff is entitled to compensation for the entire damage suffered. If the hurdle is not cleared, the plaintiff walks away empty-handed.

Proponents of the "loss of chance" doctrine argue that even if a plaintiff cannot prove on the balance of probabilities that the defendant's negligence caused his injury or damage, a claim should be allowed if the plaintiff can prove that the defendant's negligence reduced the chances of a better outcome. The plaintiff must show that he had a chance of a better outcome (even if this is < 50%), and the defendant's negligence diminished or eliminated that chance.

As the Court of Appeal decided that the Appellants had proven on the balance of probabilities that Mr Traynor would have been completely cured but for the Respondents' negligence, there was no need for them to express a view as to whether the trial judge was correct to have recourse to the minority's reasoning in Gregg v Scott on the loss of chance doctrine, or to have used a "lost years" approach.

Indeed, Singapore courts have yet to come to a clear position on these issues. In another recent medical negligence case, Noor Azlin bte Abdul Rahman v Changi General Hospital Pte Ltd and others [2019] 1 SLR 834, the Court of Appeal (and the trial judge) did not directly deal with the Appellant's argument that her chances of surviving beyond the five-year point were reduced by the Respondents' alleged delay in diagnosis.

Why have the Singapore courts refrained from ruling definitively on this question? In short, this is an intriguing and difficult topic which has seen compelling arguments by both camps. Whether loss of chance claims in clinical negligence should be allowed ultimately boils down to a choice between doing substantive justice to individual claimants and opening the door to potentially unlimited liability for defendants and their insurers. The wide-ranging commercial consequences and disruption to the existing fabric of the law must be very carefully weighed before such a momentous decision is made. It is our view that a prudent court would understandably prefer to decide a claim based on the established "but for" test if the facts of the case lend themselves to it.

As noted by Lord Hoffmann on behalf of the majority in Gregg v Scott, a wholesale adoption of possible rather than probable causation as the criterion of liability would likely open the proverbial floodgates and lead to expansion of liability. Proving that a defendant's negligence has caused the plaintiff to lose a chance (even if the original chance of a better outcome was less than 50%) is a comparatively lower hurdle for the plaintiff than the traditional "but for" test which operates on the balance of probabilities.

Be that as it may, some argue that common sense justice requires an offer of some damages to represent the loss of chance, rather than a black-and-white approach to accepting or rejecting a claim wholesale. Lord Nicholls observed in Gregg v Scott that it is "rough justice indeed" for a patient with a 60% chance of recovery reduced to a 40% chance due to medical negligence to be able to obtain compensation, but to have no recourse if his prospects are reduced from 40% to nil. However, the problem with this approach is that almost every clinical negligence claim can be formulated as a loss of chance claim, and doctors and hospitals may have to compensate patients even in cases where they are unlikely to have caused the outcome complained of (e.g. where a patient has only a 20% chance of a good outcome to begin with, which was lost due to a doctor's negligence).

Difficult questions thus remain unresolved. As the Court of Appeal has yet to reject the "loss of chance" doctrine, we expect plaintiffs to continue deploying loss of chance arguments in medical negligence claims, as an alternative or secondary line of attack to buttress a primary argument based on the orthodox "but for" test. However, it should be borne in mind that the Singapore courts have not explicitly endorsed this doctrine in the context of medical negligence claims, and for now, these remain relatively unchartered waters in the Singapore legal scene.

2. "But for" causation and the use of statistical evidence

The Court of Appeal highlighted that in most medical negligence cases, the causation inquiry may be addressed using the "but for" test, to be answered on a balance of probabilities. As demonstrated in the lengthy judgment of the Court of Appeal, majority of which was spent grappling with the causation questions, the apparent simplicity of the "but for" test is deceiving.

The Court of Appeal astutely observed that there is a conceptual distinction between fact probability and belief probability, and both of these should be considered in any causation inquiry. Fact probability refers to the causal connection between the defendant's acts and the pleaded damage. Belief probability is the degree of overall strength and credibility attributed by the decision maker to the fact probability evidence.

Statistical evidence only goes towards showing fact probability. The legal significance of such statistical evidence depends on the belief probability i.e. the level of confidence the court holds in it. In other words, statistical evidence showing a 70% likelihood that the pleaded damage was caused by the defendant's conduct does not automatically mean that the "but for" test for causation is satisfied.

Indeed, the Court of Appeal noted that epidemiological studies are concerned with large groups and populations rather than individuals. Although proper scientific interpretation may mean that the correlations within the studies might lend weight to an inference of causation, they cannot in the individual case conclusively prove causation.

All this is to say that courts will examine all of the available evidence in coming to a decision on causation, and will not simply take statistical evidence at face value. Litigants have to be aware of the likely weight of statistical evidence they choose to adduce in proving their case on causation.

3. Use of expert evidence in establishing causation

The Court of Appeal unequivocally stated that the well-known Bolam-Bolitho test, which is used in determining the question of breach, has no part to play in the causation inquiry. The Court of Appeal explained that the Bolam-Bolitho test is concerned with a potential diversity of views as to the standard of care, which is a quasi-normative question (i.e. what the doctor ought to have done), and not with a diversity of views as to causation, which is a purely descriptive question (i.e. did X cause Y?)

Relatedly, it was clarified that in considering expert evidence, the courts are not bound to accept any opinion in its entirety. While it is true that where there is no contrary evidential basis, a court should not adopt an alternative theory unfounded on evidence, it is not true that the court is bound to undertake a binary choice wherever medical evidence is proffered (and certainly not a binary choice as to the entirety of an expert's evidence). Ultimately, courts will consider the consistency, logic and coherence of an expert's evidence in deciding whether to accept or reject it, in whole or in part.


The Court of Appeal's decision in this case provides valuable insight on the challenging and complex concept of causation, and has articulated several useful principles to guide litigants and courts in future cases. However, the issue of loss of chance and whether it is an actionable claim in medical negligence cases remains unresolved. It remains to be seen whether the opportunity will arise for the Singapore courts to substantively consider these intriguing legal conundrums at a later date.

Dentons Rodyk thanks and acknowledges associate Sarah Lim for her contributions to this article.

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