Second, they can also be used as an alternative means for determining the
probability that facts given in observational evidence are true. Here the court
will use two means of assessing probabilities. (i) The court will assess the
probability by reference to the two evidentiary theorems. (ii) The court can
also test it by reference to patterns of behaviour. To do this the court will ask
itself: “Does the witness’ account of the facts ring true? Does it describe the
world working in a way that it normally works?” It is because courts almost
naturally assess observational evidence in this way that a lawyer will try to
present a persuasive theory that explains all of the undeniable facts and also
explains the disputed facts in a way that is both plausible and favourable to
their client.
Causation
Inference based on causation underlies scientific evidence. For example, a
forensic etymologist might be able to testify as to the approximate time of
death of a person due to the existing and breeding state of maggots on
a
corpse. There are three items here:
(1)
The evidence as to the time of death is based on a foundational fact
(FF) namely the presence of maggots on their corpse.
(2)
The scientist has gathered these maggots and subjected them to testing
and analysis to determine their breeding state. This is a scientific process (SP).
(3)
Causation comes from a scientific rule (SR). This rule describes the
breeding activities and cycles of maggots.
These three items are combined to produce a conclusion about the
approximate time of death. This is a derived fact (DF). The probability (P) that
the derived fact is true depends on the probabilities of the three items involved,
the probability that the foundational facts is true, P(FF), the probability that the
relevant scientific rule is true, P(SR), and the probability that the process
utilised to establish the truth of the derived fact, given the truth of the
foundational fact, is totally reliable, P(SP). Given this, the probability that the
derived fact is true, P(DF), is the multiple of the other three probabilities. That
is P(DF) = P(FF) x P(SR) x P(SP).
Step 3: Standard of Truth
At this stage,
the court has before it, because of Step 1, the versions of the
facts of the case alleged by each party and presented in their evidence. In Step
2 the court has also assessed the probability that each version is true. Now, in
Step 3, the court compares this probability to ascertain if the party initiating the
proceedings has discharged the required standard of truth, which lawyers refer
to as the standard of proof. In civil matters, of course, this is generally proof
on the balance of probability or the preponderance of evidence, which is 51%.
In criminal matters it is proof beyond all reasonable doubt, which is not
equated with any agreed numerical probability. In some cases the standard
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