Two Possibilities
Discussion in this chapter is divided into two parts to cater for the two
possibilities that can arise here. One possibility is that each overall version of
the facts is a party’s complete case. This means there is one version of the
overall facts. The other is that a party’s case consists of two or more overall
versions of the facts.
One Version
Introduction
Tasks
Here we consider the case where there is just one version of the overall facts in
a case. To work out the probability that it is true it is necessary to do two
things. First, we take each specific version of the facts and work out the
probability that it is true. This was done in the previous chapter. Second, we
use these probabilities to calculate the probability that the overall version of the
facts, constituted by all these specific facts, is true.
Two Contrasting Situations
There are two contrasting situations to consider. One is where the truth of a
specific fact is dependent on other specific facts. Here the truth of these facts
tends to rise and fall together. The other is where the truth of a specific fact is
independent of the truth of any other fact.
To explain these we will first set out an illustration. We use this illustration to
explain how we calculate the overall probability for independent facts and
dependent facts in turn.
Illustration
To illustrate the task we will consider a case where there is a cause of action,
which has four elements, namely Elements 1-4. An overall version of the facts,
therefore, consists of Facts 1-4 because these satisfy Elements 1-4 of the
plaintiff or prosecutor’s cause of action. For convenience in the discussion
which follows we refer to a plaintiff, but this is just a way of referring to
whatever party is bringing the case be they a plaintiff in a civil case or a
prosecutor in a criminal case.
Dependent and Independent Facts
Facts A and B are dependent when the truth of Fact A has a bearing on the
truth of Fact B. In the extreme case they rise and fall together – If Fact A is
true Fact B is true, and if Fact A is false Fact B is false.
Facts A and B are independent when what happens to one of them has no
bearing on what happens to the other. Thus facts are independent for the
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