These study tips are designed to clarify key points and help you to avoid errors that students commonly make. Review the Tips for Success as you study each chapter and review them again after you have studied each chapter.

1. You should be thoroughly comfortable with the material in Chapter 7, particularly the basic logic and procedures of the t test before going on to the material in this chapter.
2. The comparison distributions for the t test for dependent means and the t test for independent means have similar names: a distribution of means of difference scores, and a distribution of differences between means, respectively. Thus, it can be easy to confuse these comparisons. To remember which is which, think of the logic of each t test. The t test for dependent means is involves difference scores. So, its comparison distribution is a distribution of means of difference scores. The t test for independent involves differences between means. Thus, its comparison distribution is a distribution of differences between means.
3. You know you have made a mistake in figuring S²_Pooled if it does not come out between the two estimates from of the population variances. (You know you have made a mistake if it does not come out closer to the estimate than the larger sample.)
4. Remember that when figuring estimated variances, you divide by the number of degrees of freedom. But when figuring the variance of a distribution of means, which does not involve any additional estimation, you divide by the actual number in the sample.
5. Notice that, in the example on page 292, the value for S²_M1, is the same as the value for S²_M2. This is because there was the same number of students in the two groups (that is, N₁ was the same as N₂). When the number of individuals in the two groups is not the same, the values for S²_M1 and S²_M2 will be different.
6. We recommend that you spend some time carefully going through Table 8-6 on page 303. Test your understanding of the three kinds of t tests by covering up portions of the table and trying to recall the hidden information. If you are at all unsure about any information in the table, be sure to review the relevant material in this chapter and in Chapter 7.