9.3: Comparing Within-Subjects and Between-Subjects Designs

• What is an advantage of a within-subjects designs?

  One advantage of a within-subjects design is that it requires relatively few participants in comparison to between-subjects designs. This is useful in situations in which participants are difficult to find.
• What are the two disadvantages of a between-subject design relative to individual differences?

  1. Individual differences between groups become a confounding variable; if the individual in one treatment condition are noticeably different from the others, then the individual differences explain the differences not the treatment.
  2. The individual differences within each treatment condition can create high variance, which can obscure ay differences between treatments.
• What are the disadvantages of within-subjects design?

  • Each participant goes through a series of treatment conditions, with each treatment administered at a different time. With each treatment, there is an opportunity for time-related confounding variables.
  • Participant Attrition: The loss of participants over time.
• What are the three factors that differentiate within- and between-subjects design?

  1. Individual differences.
  2. Time related factors and order effects.
  3. Fewer participants.
• Matched-Subjects Designs?

  Each individual in one group is matched with a participant in each of the other groups. The matching is done so that the matched individuals are equivalent with respect to a variable that the researcher considers to be relevant to the study.
• What does a matched-subject design do?

  It elimiantes the problems associated with between-subjects experiments (individual differences) and the problems associated with within-subjects experiments (order effects).