(3)
The probability that the process utilised to establish the truth of
the
derived fact, given the truth of the foundational fact, is truly scientific: 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).
Real Evidence
Subject to some important qualifications, real evidence is generally reliable.
For example if a witness produces a document, a gun or some other object
that is part of the facts then it is likely to be a good representation of the way
that the document, a gun or object was at the time of the events giving rise to
the case. The relevant qualifications are such things as whether the witness is
speaking the truth when identifying the object, and whether the object has
changed or been altered since the occurrence of the events. Subject to
considerations of this kind, the court has the real thing.
Recorded Evidence
Some recorded evidence such as a video or similar media (for example, sound
recorded material or digitally recorded material, such as DVDs, CD-ROMs) is
also very reliable in principle. However, there are some important
qualifications. First, it must be a recording of the actual events. Second, it
must not have been altered. Advances in technology now make this an
important qualification because it is possible to alter a video or similar media in
a way which can be hard to detect without special equipment. Third, while a
recording may show many things clearly, it may sometimes be open to
interpretation.
4. Combination of Methods
Methods of proof can be used in combination. Frequently this happens where
there is evidence before the court based on observation. The truthfulness of
this evidence can be tested by two means that are used concurrently. (i) It can
be assessed by the means that directly apply to observational evidence. (ii)
Commonly it is also assessed by resort to inference based on patterns of
behaviour. Does the evidence, the court says to itself, tell of facts that happen
in the way that things usually happen? Alternatively, is there some inherent
improbability in the account of the facts that the evidence gives? In other
words, how likely it is that the facts occurred in the way that the witness
claimed?
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