By Louise Cantrill, Partner & Mason Thomas, Graduate Lawyer
The recent decision of East Metropolitan Health Service v Ellis (Ellis) in September this year provides an interesting discussion on the general principles of causation and how causation may be established pursuant to s 5C of the Civil Liability Act 2002 (WA), and various other statutory equivalents.
It also grapples with the ongoing conflict between the concept of causation from a medical or scientific viewpoint and apportioning liability in law, particularly when the scientific literature is uncertain as to the precise cause of the damage.
The case concerned the negligent use of a vacuum extraction device by an obstetrician during labour to help assist the delivery of Master Cooper Ellis. Soon after Cooper was delivered, it was discovered that he had suffered periods of perinatal asphyxia (a lack of oxygen or blood supply). Cooper through his next friend and father claimed to have suffered significant injuries in the course of his birth, and that those injuries were caused by the negligence of the doctor.
The matter was heard at first instance in the Western Australia District Court in 2018 before Gething DCJ, who found the obstetrician (for whom the Health Service was responsible) was negligent in the management of Cooper’s birth causing him developmental and cognitive impairments. The Health Service appealed to the Court of Appeal, where it was dismissed.
Both judgments consider extensive expert evidence from both sides. However, this note is limited to the case’s discussion of causation principles.
Establishing a cause of action
At risk of stating the obvious, the purpose of establishing causation is to apportion responsibility. The court therefore needs to be satisfied, on the balance of probabilities, the negligent act by the defendant caused the damage of the plaintiff. The various statutory tests set out a two-pronged test wherein the following is to be considered: “but for the negligent act, would the harm nevertheless have occurred?”. If so, then the negligence is said to be a “necessary condition of the occurrence of the harm”.
Understanding the legal concept of causation
The legal concept of causation is, however, distinct from that shared amongst the sciences. The latter is concerned with “explaining phenomena by reference to the relationship between conditions and occurrences”. In law, on the other hand, discussions of causation are aimed at apportioning legal responsibility. A court may therefore hold a person responsible for damage even if their wrongful conduct is “one of a number of conditions sufficient to produce that damage.”
Expert evidence submitted by the parties suggested Cooper most likely developed Hypoxic ischemic encephalopathy (HIE) from impaired blood flow and oxygen delivery to the brain during birth. Of children with stage 1 HIE, 90% are expected to have normal neurodevelopment. It was more likely Cooper’s periods of perinatal asphyxia would not develop into neurological deficits.
How, then, can the court attribute certain legal responsibility on the doctor?
As cited by their Honours in Ellis, French CJ explains in Amaca v Booth, considered the leading authority in this respect, that:
“an after-the-event inference of causal connection may be reached on the balance of probabilities notwithstanding that the statistical correlation between the first event and the second event indicated, prospectively, no more than a ‘mere possibility’ that the second event would occur given the first.” 
In this context, their Honours considered the relevance of such expert evidence as to ‘possibilities’. That is to say, where the aetiology is uncertain, experts serve to provide evidence of possibilities about whether the damage was caused by the wrongful act.
The trial judge was entitled to consider and combine primary facts and expert evidence “like strands in a cable rather than links in a chain”. Their Honours agreed the evidence did not need to set out precisely how the doctor’s negligence was the probable cause of the damage, provided the facts “supported a reasonable and definite inference that there was such a causal link”.
The case provides an interesting judicial application of s 5C of the WACLA to establish causation. It also contends with the need to be pragmatic, and confirms the courts ability to make binding decisions in apportioning legal liability and responsibility in circumstances where current scientific knowledge is unable to confirm a causal connection between an act and injury.
Expert witnesses are particularly relied upon to give evidence where the facts of the case extend beyond the level of layperson knowledge. The courts are restricted to some degree as to the inferences and connections they may draw, particularly when actively refuted by expert evidence. However, the court ultimately has the authority to make conclusions on causation without direct medical evidence to support it, as long as there is enough evidence that can be drawn together like strands in a cable to establish causation.
 East Metropolitan Health Service v Ellis (by his Next Friend Ellis)  WASCA 147 (Ellis).
 Civil Liability Act 2002 (WA) (‘WACLA’)
 NSW: Civil Liability Act 2002, s 5D; ACT: Civil Law (Wrongs) Act 2002, s 45; WA: Civil Liability Act 2002, s 5C; NT: No equivalent; Qld: Civil Liability Act 2003, s 11; SA: No equivalent; Tas: Civil Liability Act 2002, s 13; Vic: Wrongs Act 1958 s 51,
 Tabet v Gett (2010) 240 CLR 537 at .
 Ellis , citing March v E & MH Stramare Pty Ltd (1991) 171 CLR 506, 509 (Mason CJ)
 Amaca Pty Ltd v Booth  HCA 53; (2011) 246 CLR 36 (“Amaca”) .
 Ibid 
 Ibid .
 Ibid .
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