purposes of proof when the truth of Fact A has no bearing on the truth of Fact
B.
Justice David Hodgson of the New South Wales Supreme Court has
commented that in reality facts in a case as presented by counsel are more
likely to be dependent than independent. Obviously the major reason for this
arises from the common practice of each party proposing a persuasive theory
based on an hypothesis as to the overall facts; His Honour, however,
perceptively points out that because it is still a possibility that facts are
independent “courts should generally be aware of the underlying mathematical
rules”.
634
Independent Facts
In the illustration depicted above the facts are Facts 1-4. Here we assume that
they are independent. When the court hears the case it then finds the
probability of truth for each fact. Assume that it finds the following
probabilities:
Fact
True
False
Total
Fact 1
60%
40%
100%
Fact 2
80%
20%
100%
Fact 3
75%
25%
100%
Fact 4
60%
40%
100%
Figure 24.1 Independent Facts
Where the facts are independent we use the product rule to calculate the
overall probability by multiplying together the probability for each specific
fact, Facts 1-4 in the illustration, to obtain the probability that all of the facts
are true:
Probability
= P (Fact 1) x P (Fact 2) x P (Fact 3) x P (Fact 4)
= (0.60) x (0.80) x (0.75) x (0.60)
= 0.216
= 21.6%
Figure 24.2 Independent Facts: Calculations
These calculations show that the probability that Facts 1-4 are all true is 21.6%.
634
Hodgson (1995) pp 746-748. See also Rose v Abbey Orchard Property Investment
[1987] Aust Torts Reports 80-121. A possible explanation of why facts are more
commonly dependent than independent is that, by their nature, facts establishing a
cause of action will be linked. This is reflected in the need for a court to find a coherent
overall account of the facts, often referred to as a persuasive theory.
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