2.4 p-Values

Formally, the conclusion of a statistical hypothesis test is to 'reject' or to 'not reject' the null hypothesis at a pre-set significance level. Another way to convey a test's level of significance is with its p-values. The p-value is the actual probability of obtaining the calculated test statistic or a value in a more extreme part of the rejection region, when H₀ is true.

In the alkaline phosphatase example discussed previously, the test statistic of Z₀ = 1.33 is obtained. The p-value is computed as