Chapter 2 – Comparing two designs (or anything else!) using independent sample T-tests

This chapter considers the comparison of two means when you have independent samples. This usually means in practice that you have two different groups of people comparing either the same or different variables. For example, you may be considering mean satisfaction (the dependent variable) of a specific design for two different categories of people—e.g., experts vs. novices (the independent variable); or you may be comparing the mean satisfaction level for two different designs, with each design having its own evaluation sample of people. Or the quantity of interest might be the time to complete a task (e.g., make a purchase of a particular product on a particular Web site), or a myriad of other variables. In all these cases, we use what is called the two-sample t-test for independent samples. This chapter discusses and illustrates this technique, and goes into detail instructing the reader on how to perform the test using Excel and SPSS, and how to interpret the results.