See two-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 either the alternative hypothesis that μ < μ₀ or the alternative μ > μ₀ (but not both). For example, a significance level 5%, one-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