A decision rule for rejecting the null hypothesis in favour of the alternative. The rejection rule can be based on the range of values for the test statistic or on the p-value. When the test is based on a statistic, the rejection rule is to reject the null hypothesis in favour of the alternative if the value of the test statistic obtained from the sample falls in the region of values, called the rejection region, that would have only low probability to be drawn from the distribution of this statistic under the null hypothesis. Alternatively, the rejection rule is to reject the null in favour of the alternative if the p-value is less than a pre-specified significance level.