With thanks to Phil Gleeson for noting the publication of reasons for judgment in East Metropolitan Health Service v Ellis  WASCA 147 (on JADE).
There was no challenge to the findings of negligence by the primary judge. The Court, in a single judgment, dismissed an appeal by the Health Service which covered 22 different grounds of appeal, focusing on causation, with some overlapping themes (see ).
This note is not aimed at the extensive expert evidence, but rather to the discussion of causation principles and the helpful clarification of some first instance remarks in Western Australian cases about ‘appropriate case’ causation. A case is not an ‘appropriate case’ merely because the plaintiff has failed to discharge his or her onus under s 5C(1)(a). Something more is required.
Factual causation and inferences.
Turning to the issues of principle regarding factual causation, the Court said:
 It is clear, and there can be no doubt, that mere proof by a plaintiff the possibility that a defendant’s breach caused the plaintiff to suffer harm is insufficient. The court must be satisfied that it is more probable than not that the defendant’s breach caused the relevant harm; it is not sufficient to conclude that the breach may have been a cause of the harm.
 At the same time, it is also well‑established that causation may be proved by inference. If direct proof is not available, an inference of causation may be drawn if the circumstantial evidence is sufficiently strong and coherent to support a definite inference to that effect. Before such an inference can be drawn, there must be more than two conflicting inferences of equal probability.
 …in cases where expert evidence is led bearing upon a question of causation, the court must consider, and reason with reference to, the expert evidence led. However, nothing …. requires a plaintiff to prove, or a trial judge to find, by reference to expert evidence, the specific mechanism by which one event caused another event.
 A court may draw an inference of causation notwithstanding that, in the particular case, expert witnesses do not express an opinion that the damage was caused by the relevant breach. An inference of causation may be drawn without medical evidence to support it, or when the expert evidence does not rise above the opinion that a causal connection is possible if, but only if, the materials as a whole justify an inference of probable connection.
 In circumstances where the aetiology is uncertain, or subject to significant scientific dispute, the courts are not thereby disabled from making decisions as to causation on the balance of probabilities….
 Evidence of possibility, including epidemiological studies, can therefore be regarded as circumstantial evidence which may, alone or in combination with other evidence, establish causation in a specific case. As in any circumstantial case, an inference as to the probabilities may be drawn from a number of pieces of particular evidence, each piece of which does not itself rise above the level of possibilities.
 Causation, like any other fact to be established by a process of inference, may be established by a process that combines primary facts like strands in a cable rather than links in a chain. In those where the evidence does consist of strands in a cable, rather than essential links in a chain, as long as the ultimate inference is reached to the required standard, it is not necessary for an intermediate fact to be established to the legal standard. This principle of course applies, in a criminal case, to proof beyond reasonable doubt; a fortiori it applies to the proof of causation on the balance of probabilities.
The findings on appeal meant that it was not strictly necessary for the Court to address the remarks of the primary judge in respect of section 5C(2) of the Civil Liability Act, being the “appropriate case” sub-section. However the Court went on to do so as the issue was fully argued.
Section 5C(2) of the Civil Liability Act is an alternative means of establishing factual causation in ‘an appropriate case’ where ‘a fault that cannot be established as a necessary condition of the occurrence of harm’. Where fault can (and is) established as a necessary condition of the occurrence of the harm, s 5C(2) is irrelevant. The application of s 5C(2) (where it is said to apply) calls attention whether the instant case is ‘an appropriate case, in accordance with established principles’ (see , ).
The appellant contended that the learned trial judge erred in law in applying the notion of ‘material contribution’ to harm as an established principle giving rise to an ‘appropriate case’ within the meaning of s 5C(2). As part of that contention, the appellant submits that his Honour gave no reason for his conclusion that the present case was an appropriate one for the application of s 5C(2). In that regard the Court held at :
We accept the appellant’s submissions in this regard. In our respectful view, the learned trial judge’s analysis of s 5C(2), and in particular his Honour’s approach of the notion of ‘material contribution’ in that context, confused the important difference between s 5C(1)(a) and s 5C(2). Whether, and in what way, ‘material contribution’ might have a role to play in the application of s 5C has yet to be finally determined. Nevertheless, it does not operate in the manner that the learned trial judge appears to have applied it in Primary reasons…
The Court went on to discuss the various ways in which ‘material contribution’ has been used and said at  that ‘material contribution’ is picked up in s 5C(1)(a), in the requirement that the plaintiff establish ‘that the fault was a necessary condition of the occurrence of the harm’ (as opposed, for example, to ‘the necessary conditions’).
However referring then to a discussion in Strong v Woolworths Ltd regarding Bonnington Castings, the Court said at 
Material contribution’ in this sense is applied in a context where the ‘but for’ test cannot be applied. In Bonnington Castings Ltd v Wardlaw, this was because it could not be said that without (‘but for’) the ‘quota of silica dust’ contributed to by the negligence of the appellant, Mr Wardlow would not have developed the disease. And that was, in turn, because it was the accumulated gradual exposure to silica dust that had caused the disease, and no single part of that accumulated exposure could meet a ‘but for’ test.
The Court concluded at  and .
As is apparent from the text of s 5C(2), it is concerned with an ‘appropriate case’ in which by reason of the particular circumstances fault ‘cannot be established as a necessary condition’. The word ‘cannot’ is, in our view, significant in this context. Section 5C(2) is not concerned, in our view, with a case in which evidence ‘does not’ establish factual causation (in the sense that there could be evidence to support a finding of a necessary condition, but no such evidence is adduced). It is concerned, rather, with a case in which there ‘cannot’ be such evidence because of the nature of the case.
The metes and bounds of what is an ‘appropriate case’ for the purposes of s 5C(2) of the Civil Liability Act remain to be determined. It is clear, however, that s 5C(2) does not apply merely because a plaintiff is only able to prove that the defendant’s fault may have been a cause of the harm. A case is not an ‘appropriate case’ merely because the plaintiff has failed to discharge his or her onus under s 5C(1)(a). Something more is required.