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# 5 Numbers

Both lawyers and laypeople often struggle with numbers. The Latin phrase ‘iudex non calculat’ (a judge does not calculate) means that it is the quality and not the quantity of arguments that counts – but some lawyers jokingly take it to mean that judges are not good at maths. While there is some truth that lawyers and laypeople can be uncomfortable with the numbers often used in expert evidence, there are ways of overcoming this problem.

In Box 4, you will be reminded about probabilities, a mathematical idea that underpins much of expert evidence.

## Box 4 About probabilities

Much expert evidence is discussed in terms of numerical probabilities. These can be expressed as a percentage where 0 per cent is impossible and 100 per cent is a certainty (see Figure 13), or as a number where 0 is impossible and 1 is a certainty.

Figure 13 The scale of probability
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- 1 Times, January 10, 1994.

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