They then considered the possible decisions after a hypothesis test, which are either to reject a null hypothesis in favour of the alternative, or not to reject the null.fn6 Two types of mistake are therefore possible: a Type I error is made when we reject a null hypothesis when it is true, and a Type II error is made when we do not reject a null hypothesis when in fact the alternative hypothesis holds. There is a strong legal analogy which is illustrated in Table 10.6 – a Type I legal error is to falsely convict an innocent person, and a Type II error is to find someone ‘not guilty’ when in
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