The decision assists defendants who are involved in cases
dealing with the development " of diseases and questions of
The legal test for causation has not changed. Plaintiffs must
show that it was more " probable than not
that the defendant's actions or omissions caused the injury,
not that " the defendant merely increased the risk or may have
caused the injury in the individual bringing the claim.
Where medical and scientific evidence is inconclusive, a
plaintiff will have significant difficulty in establishing
causation and an entitlement to damages.
Paul Cotton died of lung cancer. He was a smoker and smoked
between 15 and 20 cigarettes a day for 26 years. He had also had
light exposure to respirable asbestos fibres over 15 years in the
course of his employment. After Mr Cotton died, the executor of his
estate sought compensation on the basis of his exposure to asbestos
in the workplace.
The trial judge said that the plaintiff would succeed if the
evidence supports the conclusion that, on the probabilities, his
cancer was caused by the combined effects of asbestos exposure with
the effects of his chronic smoking.
The plaintiff relied on epidemiological evidence (the study of
large populations) to prove her case. She argued that:
Smoking and asbestos work together, because more people who are
exposed to both carcinogens contract lung cancer than would be
expected from exposure to 1 carcinogen;
the only 2 explanations of Mr Cotton's lung cancer that
need to be considered are smoking as the sole cause, and the
combined effect of smoking and asbestos; and
the epidemiological evidence shows that both exposure to
tobacco smoke and asbestos is more dangerous than exposure to one
or the other, and accordingly, exposure to both carcinogens was
probably the cause of Mr Cotton's cancer.
None of the expert medical witnesses could definitively
attribute Mr Cotton's cancer to the smoking or the asbestos or
both carcinogens. Further, none of the witnesses assigned a greater
than 23% to the chance that Mr Cotton's cancer was caused by
his exposure to asbestos, but assigned a much high probability of
no less than 67% to the cancer being caused by smoking alone.
The trial judge however rejected the approach which looked at
the probabilities of each individual cause of lung cancer, because
of medical evidence which suggested that smoking and asbestos
exposure has a cumulative effect. Based on that evidence, the trial
judge decided that the relevant causal connection existed between
the defendant's negligence and the damage suffered.
The defendants appealed the decision.
Court of Appeal
The Western Australian Court of Appeal upheld the trial
High Court Decision
The High Court disagreed with the approach taking by the trial
judge and the Court of Appeal. In short, the High Court said that
Mr Cotton's lung cancer could not be attributed to asbestos
exposure. The High Court did not accept the plaintiff's
proposition that because exposure to both carcinogens is more
dangerous than exposure to one, smoking and asbestos must work
together and they must have worked together in this case. The court
held that the epidemiological evidence did not establish this. The
evidence showed that it was more likely that Mr Cotton's lung
cancer was caused by smoking, and the expert witnesses unanimously
agreed that the risk of contracting lung cancer from smoking was
"no scientific or medical
examination can now say, with certainty, what caused Mr
Cotton's cancer or lung cancer."
" "...despite this uncertainty, the courts must, and do,
"reduce to legal certainty [a question] to which no other
conclusive answer can be given". The courts do that by asking
whether it is more probably than not that X was the cause of Y.
Saying only that exposure to asbestos may have been a cause of Mr
Cotton's cancer is not a sufficient basis for attributing legal
responsibility. Observing that a small percentage of cases of
cancer were probably caused by exposure to asbestos does not
identify whether an individual is one of that
As such, the plaintiff had not satisfied the court that it was
more probable than not that asbestos was the causative effect of Mr
Cotton's cancer, but merely demonstrated that the inhalation of
asbestos fibres increased the risk or may be a cause of Mr
Cotton's cancer, which was insufficient to attribute legal
responsibility to the defendants.
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