SPSS Statistics Workbook For Dummies

Chapter 8

Comparing Two Groups with T-Tests

IN THIS CHAPTER

Comparing groups with the independent-samples t-test

Comparing time points or conditions with the paired-samples t-test

Viewing error bar charts

In this chapter, we explain how to compare two different groups on a continuous outcome variable. The independent-samples t-test determines if a significant difference exists between two different groups. For example, you might want to know whether one group of customers purchases more items, on average, than a second group of customers; or whether drug A reduces depression levels more than drug B; or whether student test scores in one class are higher than in a second class.

You also learn how to compare a group of people who have been assessed at two different points in time or under two different conditions, such as before and after an intervention. The paired-samples t-test determines if there's a significant difference or change from one point in time or condition to another. For example, you might want to know whether measures administered before and after some type of treatment differ; or whether differences in ratings exist between two competing products; or whether satisfaction ...