3. Independent Samples t-Test (or 2-Sample t-Test)
When to use the independent samples t-test
The independent samples t-test is probably the single most widely used test in statistics. It is used to compare differences between separate groups. In Psychology, these groups are often composed by randomly assigning research participants to conditions. However, this test can also be used to explore differences in naturally occurring groups. For example, we may be interested in differences of emotional intelligence between males and females. Any differences between groups can be explored with the independent t-test, as long as the tested members of each group are reasonably representative of the population.
Example 3.1
Suppose we put people on 2 diets: the pizza diet and the beer diet. Participants are randomly assigned to either 1-week of eating exclusively pizza or 1-week of exclusively drinking beer. Of course, this would be unethical, because pizza and beer should always be consumed together, but this is just an example. At the end of the week, we measure weight gain by each participant.
Which diet causes more weight gain?
In other words, the null hypothesis is:
Ho: wt. gain pizza diet =wt. gain beer diet.
Why? The null hypothesis is the opposite of what we hope to find. In this case, our research hypothesis is that there ARE differences between the 2 diets. Therefore, our null hypothesis is that there are NO differences between these 2 diets.
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