Two-Tail Hypothesis Test

This test is used whenever the alternative hypothesis is expressed as not equal.

The two-tailed test is a statistical test used in inference, in which a given statistical hypothesis, H0 (the null hypothesis), will be rejected when the value of the test statistic is either sufficiently small or sufficiently large. This contrasts with a one-tailed test, in which only one of the rejection regions "sufficiently small" or "sufficiently large" is preselected according to the alternative hypothesis being selected, and the hypothesis is rejected only if the test statistic satisfies that criterion. Alternative names are one-sided and two-sided tests.