Rejection region
The rejection region is the set of test-statistic values for which the null hypothesis is rejected, bounded by the critical value at the chosen significance level. A test statistic in this region is statistically significant.
FrameworkHypothesis testing
See it move
At a 5% significance level, the rejection region is the portion of the sampling distribution beyond the critical value. For a two-tailed test using the standard normal distribution, that boundary sits at ±1.96: test statistics below −1.96 or above +1.96 fall in the rejection region. The area covered by both tails equals α, the chosen probability of rejecting a true null hypothesis.
Check yourself
For a two-tailed z-test at a 5% significance level, the critical values are approximately ±1.96. A researcher calculates a test statistic of z = 2.15. What is the correct conclusion?