Decide whether to reject H0 by using the test statistic value and the critical value
\Decide whether to reject H0 by using the test statistic value and the critical value rule. Since the test statistic value z = 2.20 is greater than the critical value z.05 = 1.645, we can reject H0: μ = 50 in favor of Ha: μ > 50 by setting α equal to .05. Furthermore, we can be intuitively confident that H0: μ = 50 is false and Ha: μ > 50 is true. This is because, since we have rejected H0 by setting α equal to .05, we have rejected H0 by using a test that allows only a 5 percent chance of wrongly rejecting H0. In general, if we can reject a null hypothesis in favor of an alternative hypothesis by setting the probability of a Type I error equal to α, we say that we have statistical significance at the α level.