<P> The type I error rate or significance level is the probability of rejecting the null hypothesis given that it is true . It is denoted by the Greek letter α ( alpha ) and is also called the alpha level . Often , the significance level is set to 0.05 ( 5 % ) , implying that it is acceptable to have a 5 % probability of incorrectly rejecting the null hypothesis . </P>
the probability of making a type i error when retaining ho at the .05 level of significance is
5 %