# 10. Comparing Two Population Means

There are two types of two-sample t-tests. (The test we covered in Chapter 9 that compared the mean of one sample to a fixed number is known as a one-sample -test.) These tests are:

Unpaired or independent sample -test:

The two populations are “independent”. There is no relation between the and variables (as we’ll call them). This is a “between subjects” test, the experimental subjects in each of the two populations are different.

Paired or dependent sample -test:

There is a natural pairing between the two variables and , usually they are measured from the same subject. A paired -test is an example of a “repeated measures” or “within subject” test.

We will introduce the independent sample -test with a -test approximation first to build ideas. As before, note that SPSS doesn’t do these approximate -tests. It does -tests even for large samples.