Section 9.4 Summary

1. The test statistic used for the test for the mean is

   with degrees of freedom. The test may be used under either of the following conditions: (a) the population is normal, or (b) the sample size is large . For the critical-value method, we compare the values of and . If falls in the critical region, we reject .

2. For the -value method, we reject if the .
3. We may use confidence interval to perform two-tailed tests at level of significance for various values of .