8.1: Introduction to Between-Subject Experiments

• The major goals of the Experimental Research Strategy Are?

  1. Manipulation of one variable to create a set of two or more treatment conditions.
  2. Measurement of a second variable to obtain a set of scores within each treatment condition.
  3. Comparison of the scores between treatments.
  4. Control of all other variables to prevent them from becoming confounding.
• The Two Basic Research Design Methods:

  1. Within-Subjects Design: The different groups of scores are all obtained from the same group of participants.
  2. Between-Subjects Design: Each of the different groups of scores is obtained from a separate group of participants.
• What is the defining characteristic of a between-subject design?

  It compares different groups of individuals. A researcher manipulates the independent variable to create different treatment conditions, and a separate group of participants is assigned to each of the different conditions. The dependent variable is measured and a difference between the groups are looked for.
• What is the general goal of a between-subjects experiment?

  To determine whether differences exist between two or more treatment conditions.
• What is the relevancy of independent scores in a between-subjects experiments?

  The design allows only one score for each participant; it uses different group of participants for each level of the independent variable, and each participant is exposed to only one level of the independent variable.
• What are the two advantages of a between-subjects design?

  1. Each individual score is independent from the other score; thus, the measurement is not impacted by other treatment factors.
  2. It can be used for a wide variety of research questions. It is always possible to assign different groups to the different treatments.
• What are the two disadvantages of a between-subjects design?

  1. Requires a large number of participants. Each participant contributes only one score to the final data; thus, it is an issue involving special and small populations.
  2. Individual differences become confounding variables.
• What is the issue with individual differences?

  The concern with individual differences is that they can cause two different individuals to produce two different scores when a dependent variable is measured.

  1. Individual differences become confounding variables.
  2. Individual differences can produce high variability in the scores, making it difficult to determine whether the treatment has any effect.