Learning Objectives
- A researcher has two options in assigning participants to control and experimental conditions: between subjects and within subjects.
- For a between-subjects procedure, participants are randomly assigned to control and experimental groups. A between-subjects design ensures that participants are exposed to only one level of the independent variable—for example, a particular treatment—and not to any other types of treatment.
- For a within-subjects procedure, all participants receive all conditions of the experiment. This procedure gives birth to what is called a repeated-measures design, also known as a within-subjects design.
- Choosing a between- or within-subjects procedure depends largely on the research question under investigation, the nature of the independent and dependent variables, and the hypothesis being tested.
- Data collected in psychological experiments are commonly analyzed by testing the statistical significance of the null hypothesis, such as there being no relationship between the independent and dependent variables.
- The researcher aims to reject the null hypothesis in favor of the research hypothesis that predicts a specific relationship between the independent and dependent variables.