Ch. 11: Introduction to Factorial Designs

• Factors


  An independent variable in an experiment that include two or more independent variables OR a variable that differentiates a set of groups or conditions being compared in a research study.
• Factorial Designs


  A research design that includes two or more factors.
• What is the primary advantage of a factorial design?

  Factorial designs allows researchers to examine how unique combinations of factors acting together influence behaviour.
• What is a matrix?

  It is representative of the matrix; a structure of a two-factor design. The levels of one factor determine the columns and the levels of the second factor determine the row. Each cell in the matrix corresponds to a specific combination of factors, that is, a separate treatment condition.
• Main Effects


  In a factorial study, the mean differences among the levels of one factor.
• Interaction Between Factors


  Occurs whenever two factors, acting together, produce mean differences that are not explained by the main effects of the two factors. On the other hand, if the main effect for either factor appliex equally across all levels of the second factor, then the two factors are independent and there is no interactions.
• Combined Strategy


  A factorial study that combines two different research strategies, such as experimental and non-experimental or quasi-experimental in the same factorial design.
• In a "Combined Strategy" study, what kind of factor that is involved?

  A true independent variable that consists of a set of manipulated treatment conditions and a second factor that is a quasi-independent variable that falls into one of the two categories:

  1. Pre-existing participant characteristics such as age or gender.
  2. Time.
• Types of Order Effects in Within-Subject Designs

  1. No Order Effects
  2. Symmetrical Order Effects
  3. Nonsymmetrical Order Effects
• No Order Effects


  When there are no order effects it does not matter if the treatment is presented as first or second; the mean is the same in either case.
• Symmetrical Order Effects


  When order effects exist, the scores in the second treatment are influenced by participation in the first treatment. For this data, the order effect is symmetrical and the order effect appears in the data as a symmetrical interaction. This only exists in situations in which the order effects are summetrical.
• Nonsymmetrical Order Effects


  Order effects are not symmetrical. Participant in different treatment conditions may produce different levels of fatigue or practise.

  • The participants in group 1 received treatment 1 first. This treatment products a relatively large order effect.
  • The participants in group 2 receive treatment 2 first. This treatment produces a relatively small order effect thati ncreases the mean for treatment 1.