If not, then there is not enough evidence to reject H 0.īut how to calculate critical values? First of all, you need to set a significance level, α \alpha α, which quantifies the probability of rejecting the null hypothesis when it is actually correct.If so, it means that you can reject the null hypothesis and accept the alternative hypothesis and.Once you have found the rejection region, check if the value of the test statistic generated by your sample belongs to it: In other words, critical values divide the scale of your test statistic into the rejection region and the non-rejection region. A critical value is a cut-off value (or two cut-off values in the case of a two-tailed test) that constitutes the boundary of the rejection region(s). The critical value approach consists of checking if the value of the test statistic generated by your sample belongs to the so-called rejection region, or critical region, which is the region where the test statistic is highly improbable to lie.

The other approach is to calculate the p-value (for example, using the p-value calculator). In hypothesis testing, critical values are one of the two approaches which allow you to decide whether to retain or reject the null hypothesis.