Case Note

• Citation: (2011) 23 SAcLJ 307
• Published date: 01 December 2011
• Author: Basil C BITAS Juris Doctor (JD) (Georgetown University Law Center, Washington, DC); Member of the Bars of New York State and Washington, DC; Practice Associate Professor, School of Law, Singapore Management University.
• Date: 01 December 2011

A COMMON LAW VIEW OF CAUSATION, SCIENCE AND STATISTICAL EVIDENCE IN THE COURTROOM

Amaca Pty Ltd v Ellis

[2010] HCA 5

In March 2010, the Australian High Court in Amaca Ltd v Ellis [2010] HCA 5 (“Amaca”) moved assertively to clarify the approach of the Australian courts to causation in cases of lung disease involving multiple pathogens. The court demonstrated sensitivity to both the scientific and legal inquiries while reaffirming the obligation of plaintiffs to prove causation based on the balance of probabilities. In examining the plaintiff ‘s statistical evidence, the court established important guideposts regarding the proper use and interpretation of epidemiology in the courtroom, highlighting both the relevance and limits of such proof regarding causation and the satisfaction of the plaintiff ‘s evidentiary burden. While Amaca dealt with lung cancer, asbestos and cigarette smoking, the court‘s careful approach to the statistical evidence and reaffirmation of the common law standard of “but for” causation are likely to resonate beyond the asbestos field to cases involving other complex diseases arising from a range of low-level occupational and environmental exposures. The High Court has established a practical and useful road map for the manner in which courts should integrate scientific proof into the inquiry while preserving the fundamental aspects and related application of the common law doctrine of causation.

I. Introduction

1 In Amaca Pty Ltd v Ellis as Executor of the Estate of Cotton (deceased); South Australia v Ellis; Millenium Inorganic Chemicals Ltd v Ellis1 (“Amaca”), a decision rendered by the Australian High Court on 3 March 2010, the justices moved assertively, and, indeed, unanimously to reaffirm the relevance and precise application of the common law “but for” standard for determining causation in cases of complex multifactorial pathogenesis. The case, which involved an individual‘s development of lung cancer following the cumulative exposure to asbestos and cigarette smoke, is noteworthy to the extent that it (a) clarifies the standard of causation in such cases within Australia‘s federal system; (b) underscores the importance of examining and interpreting the scientific evidence adduced; (c) highlights the challenges, potential and limits of the dialogue between the medical and legal spheres; and (d) suggests a more conservative or traditional approach to the issue of causation, where diffuse risks cannot be definitively quantified or parsed. The exposures brought about by industrial society may be many and varied, but the justices in Amaca have now reaffirmed that the complexity and overlapping nature of these exposures cannot be used indiscriminately to relax the evidentiary burden where causation is at issue. Amaca is likely to resonate beyond the asbestos field as courts in Australia and elsewhere deal with diffuse, but low-level risks arising from rapid growth and the development of new industries.

II. Facts

2 Paul Cotton was a regular cigarette smoker of between 15 to 20 cigarettes per day for 26 years. He was also exposed to asbestos during two periods of employment, one with the Engineering Water Supply Department of the State of South Australia from 1975 to 1978, where he worked with asbestos-lined pipes manufactured by Amaca (formerly James Hardie & Coy Pty Ltd), and later in his work with Millennium from 1990 until his death from lung cancer in 2002.

3 Mr Cotton‘s executrix secured a favourable judgment against his two employers and Amaca at the trial court level in the Supreme Court of Western Australia and later prevailed on appeal in a majority opinion issued by the West Australian Court of Appeal, with Martin CJ dissenting.

III. Issue

4 Amaca and the other original defendants were granted special leave to appeal to the High Court on the issue of causation. Issues of breach of duty and foreseeability of injury were not in question. Accordingly, the question at issue can be framed as whether, in the presence of a breach of duty where injury was reasonably foreseeable, the balance of probabilities concerning causation justified a finding that Amaca‘s specific breach and/or that of the other defendants led to the plaintiff ‘s illness?

5 How should the court interpret the causative role of the decedent‘s exposure to respirable asbestos, an acknowledged risk factor for lung cancer, where the plaintiff ‘s history also revealed a long and substantial history of cigarette smoking also closely associated with the pathology at issue? The case therefore essentially involved the analysis of a complex multifactorial, or synergistic, disease process within a legal setting.

6 How does one assess and parse risk in such a situation and can liability be assessed and apportioned before causation itself is conclusively proved or otherwise plausibly established? To what extent can the court infer causation? It is the answer to these questions that highlights the difference between the nature of the scientific and the legal inquiries and that further yields the relatively “bright line” test of “but for” causation that separates the two.

IV. Applying the standard and interpreting scientific evidence in the courtroom - Causation and material contribution

7 The history of Amaca2 through the Australian court system highlights the collision, or evolving co-existence, of legal concepts with scientific, probabilistic analysis. While the case nominally dealt with the application of the “but for” or balance of probabilities standard to determine causation, it is clear that the disparate interpretation of the scientific evidence by the trial, appellate and high courts conditioned the interpretation and application of the relevant standard. The courts‘ understanding of the pathology and related interpretation of the scientific evidence adduced in support of the plaintiff ‘s claim resulted in the operational application of different tests at the trial and appellate levels as compared to that of the High Court.

8 In cases of complex disease processes involving lung carcinogens, Australian courts in certain states had witnessed a qualified

relaxation of the standard of proof, relying, inter alia, on the House of Lords decision in Bonnington Castings Ltd v Wardlaw3 (“Bonnington Castings”). With regard to complex disease processes involving lung pathology, the court in that case asked whether the plaintiff ‘s exposure to silica dust was a cause or otherwise made a material contribution to the plaintiff ‘s development of pneumoconiosis, adding that any exposure above a de minimis level could be deemed to be material.4 In Bonnington Castings, the plaintiff ‘s exposure to silica dust, a principal cause of pneumoconiosis, came from two sources, a pneumatic hammer and swing grinders, only one of which involved a breach of duty potentially triggering legal liability. Moreover, it was well established as a medical matter that the pathology develops over time from the cumulative exposure to silica dust. Accordingly, in a case where (a) silica‘s role as a cause was well accepted and (b) the cumulative nature of the disease process was understood, the court found it logically and legally plausible to ascribe legal liability to the defendant whose breach of duty exposed the plaintiff to only one source of the contaminant.

9 As a predicate to the analysis of Amaca,5 it is important to note the following. The plaintiff ‘s exposure in Bonnington Castings6 dealt with two sources of exposure to the same contaminant. Silica‘s role as a cause of the pathology in question was beyond medical question. Accordingly, there was no issue concerning the point at which to draw a causal inference from statistical data. The role of cumulative exposure was also well established though here there was perhaps a question as to what constituted a material contribution. Given the strong causal connection between silica and the development of pneumoconiosis, the court felt justified in adopting the principle that any exposure above a de minimis level could be deemed to be a material contribution. It is important to note, however, that material contribution was not used to establish causation per se, but rather to define the level at which legal responsibility would be triggered, the causative role of silica as a medical matter having already been established. Material contribution was therefore used to inform and clarify the effects and application of a finding of causation (ie, to establish the scope of legal responsibility), not to substitute for proof of same.

V. Amaca distinguished and clarified

10 Amaca7 constituted an opportunity for the court to clarify the relevant standard in cases of complex lung pathogenesis. It raised considerations that resonated with those of Bonnington Castings,8 including a potentially deserving plaintiff, work place exposure, a complex disease process, and the interpretation of scientific evidence in the courtroom.

11 It did not, however, constitute a situation involving exposure to a single lung pathogen known to “cause” the condition at issue. Nor was the exposure to the pathogens at issue solely the product of the work place. Rather, Amaca9 concerned the plaintiff ‘s exposure to two different lung pathogens, cigarette smoke and asbestos, the former of which was voluntary and the latter “imposed” from the plaintiff ‘s perspective due to the conditions of the work place. Moreover, the cumulative exposure to a single pathogen was not the sole issue, but rather the separate and combined exposure of the plaintiff to two different pathogens constituted the focus of the inquiry.

12 The factual situation in Amaca10 was therefore decidedly more complex than the one at issue in Bonnington Castings11 as both a medical and legal matter. There were more permutations or causal scenarios to separate and analyse than in Bonnington Castings. Moreover, once the inquiry began...