A rational view of “irrationality” and the Civil Liability Act s5O Defence | South Western Sydney Local Health District v Gould [2018] NSWCA 69

Author: Simon Grey

Judgement Date: 13th April, 2018

Citation: South Western Sydney Local Health District v Gould [2018] NSWCA 69

Jurisdiction: New South Wales Court of Appeal (Basten JA, Meagher JA, Leeming JA)


  • The standard of care by which breach of duty is to be assessed in professional negligence cases (where s5O of the Civil Liability Act is pleaded) is whether the professional acted in a manner that was widely accepted by peer professional opinion as competent professional “practice”, subject to that opinion not being considered by the court as “irrational” (s5O(2)).
  • Professional “practice” in the context of s5O remains a reference to a particular specific practice or method of providing the services.
  • It is a ‘seriously pejorative and exceptional thing to find that a professional person [in this case, a medical expert] has expressed an opinion that is “irrational” [in the context of s5O(2)], and even more exceptional if the opinion be widely held’.


The respondent, Robert Gould, aged eight at the time, presented to the Emergency Department of Campbelltown Hospital in August 2011 with an open fracture to his left thumb. He was immediately transferred to Liverpool Hospital for treatment but later required amputation of the thumb which occurred in September 2011.

The respondent sued the appellant, South Western Sydney Local Health District (responsible for Campbelltown and Liverpool Hospitals) alleging a breach of duty of care in his treatment, resulting in the need for the amputation.

In accordance with the Uniform Civil Procedure Rules, a plaintiff is obliged to serve independent expert evidence supporting a claim of professional negligence (known as peer professional opinion). In this case, the respondent served expert evidence from an independent emergency physician. Typically, and as occurred in this case, the appellant also served expert evidence from independent doctors, namely a hand specialist/plastic surgeon and a microbiologist, in support of its defence of the claim.

In a judgment of Levy J of the District Court the appellant was found liable in negligence to the respondent for treatment of the thumb injury. Although Levy J made a number of findings of breach, only one was found to be causative of the loss of the thumb, namely a failure to administer an additional antibiotic drug (gentamycin) on the evening of the respondent’s presentation to Hospital.

The appellant’s expert evidence going to the critical issue of antibiotic management was found to be “irrational” by Levy J and accordingly the defence provided by s5O of the Civil Liability Act was unsuccessful.


The appeal

Leeming JA wrote the lead judgment with Basten JA and Meagher JA agreeing.

 “Irrationality” under s5O

Section 5O(1) of the Civil Liability Act provides that a professional does not incur a liability in negligence if that person acted in a manner that was widely accepted by peer professional opinion as competent professional practice. However, this is always subject to s5O(2), which states that peer professional opinion cannot be relied upon if the court considers it “irrational”.

The statutory meaning of “irrational” is not otherwise defined, however Gould provides guidance on the application of irrationality in the s5O defence. Leeming JA’s judgment assists in understanding how the term should be applied.

First, the statutory construction of “irrational” is not the dictionary definition of the word. Leeming JA does not define “irrational’ but cites English authority, seemingly with approval, that the body of professional opinion could not be determinative of the standard of care if it is shown the opinion “is not capable of withstanding logical analysis”. Leeming JA noted that the primary judge erred in taking into account dictionary definitions of a synonym for irrational, specifically “unreasonableness”, in order to construct a definition of “irrationality”.

Second, Leeming JA found that it is two very different things to prefer evidence for certain reasons (which courts do legitimately everyday) and to find evidence to be “irrational”. The primary judge erroneously rejected evidence as irrational on the basis that he preferred other evidence on the “basis of rationality”. Further, to the extent that the primary judge merely preferred the views of one witness over another, that rejection was inconsistent with the notion that differing peer professional opinion can be relied on and that peer professional opinion does not need to be universally accepted.

Central to the appeal in Gould was the choice of antibiotics administered to the respondent, specifically whether gentamycin should have been administered. In determining whether the appellant had a defence under s5O was the relevance and application of therapeutic guidelines for the administration of antibiotics (“the guideline”) to the professional practice under consideration. The guideline suggested the administration of certain antibiotics in the case of a child with an open wound. Gentamycin was not one of the suggested antibiotics.

The primary judge rejected the evidence of the appellant’s two experts as “irrational”. With regard to the hand specialist/plastic surgeon, the primary judge found “irrationality” on the basis of ‘incomplete consideration of relevant factual matters’. With regard to the microbiologist, the primary judge found “irrationality” on the basis that his views, insofar as they concerned antibiotic stewardship as reflected in the guideline, were “misdirected” and “overstated”.

The Court of Appeal found that neither of the appellant’s experts should have been rejected as “irrational”. First, because there was a lack of procedural fairness in circumstances where “irrationality” had not been pleaded or put to the experts.

Second, the primary judge applied the wrong legal test. “Irrationality” is distinct from admissibility. The “irrationality” test imposed by s50(2) is not dependent upon making good particular assumptions which are not established on the evidence, nor when the basis for a practice is unexplained.

The Court of Appeal found that the “irrationality” exception should only very rarely be available and it is a ‘seriously pejorative and exceptional thing to find that a professional person has expressed an opinion that is “irrational”, and even more exceptional if the opinion be widely held’.

Basten JA added that “It will only be if the court can on the evidence be satisfied that there is no rational basis for it [the peer professional opinion] that it can be rejected”. His Honour noted that this may create an evidential burden on the plaintiff and that burden will not be satisfied by evidence merely justifying an alternative approach.

The Court of Appeal found that the peer professional opinions led by the appellant were not irrational and that the appellant’s practice accorded with those opinions. It followed that s5O applied and there was no liability in negligence. On this basis, the appeal was allowed.

s5O and Evidence from Treating Doctors

In addition to the appellant’s independent experts, there was further evidence to support the conclusion of a widely accepted practice which was not irrational, namely, the evidence of the hand surgeon who operated on the respondent. The hand surgeon gave evidence addressing usual practice based on his clinical experience in various hospitals. The primary judge’s conclusions on the irrationality of the independent experts paid no regard to such evidence.

Leeming JA confirmed that it was open to the court to have regard to the hand surgeon’s evidence in order to reinforce a conclusion that not administering a certain antibiotic was a practice which was widespread. In other words, a professional defendant’s (e.g. a treating doctor’s) own evidence can be taken into account in determining whether the s5O defence is made out.

The Standard of Care

The Court of Appeal clarified the standard of care against which breach of duty is to be assessed (in professional negligence cases where the s5O defence is relied on).

In cases such as Gould, where the defendant establishes the preconditions to s5O, then there is a single standard against which the defendant is assessed, namely, the s5O standard (widely accepted by peer professional opinion as competent professional practice), subject always to the peer professional opinion not being irrational.

“Practice” for the purposes of s5O

While the judgment of Gould does not engage with this issue, it is worth clarifying the legal position as this point has been the subject of recent judicial discussion.

The Court acknowledged as a “divisive issue” [1] whether the reference to a “practice” (in the context of ‘competent professional practice’ as provided by s5O(1)) was a reference to the practice of the relevant profession, or more narrowly to a particular specific practice or method of providing services. This appeal was able to ‘put that issue entirely to one side’. Accordingly, at least for now, the latter approach as favoured in McKenna [2] remains good law.

It follows that it will assist a professional defendant’s case if guidelines or similar evidence can be used to establish a “practice” for the methods of the provision of services.




[1] Referring to the distinction captured by Simpson JA in Sparks v Hobson; Gray v Hobson [2018] NSWCA 29 at [335]

[2] McKenna v Hunter New England Local Health District [2013] NSWCA 476