See one-sided test. An hypothesis test of the null hypothesis that the value of a parameter, μ, is equal to a null value, μ₀, designed to have power against the alternative hypothesis that either μ < μ₀ or μ > μ₀ (the alternative hypothesis contains values on both sides of the null value). For example, a significance level 5%, two-sided z test of the null hypothesis that the mean of a population equals zero against the alternative that it is greater than zero would reject the null hypothesis for values of

$$ |z| = \left | \frac{\mbox{sample mean}}{\mbox{SE}} \right | > 1.96.$$