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Factorial Designs in Experimental Research

Explore the use of factorial designs in experimental research to study the effects of manipulating multiple variables on dependent outcomes. Learn about main effects, interactions, and application examples in social sciences.

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Factorial Designs in Experimental Research

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  1. Review • During the last lecture we were discussing the use of experiments as a way of answering questions about the causal relationship between variables • If we can systematically manipulate a variable and show that it has an effect on another variable, then we have a strong basis for concluding that one variable affects the other.

  2. Factorial Designs • Today we’re going to discuss experimental designs involving more than one independent variable. • Why might we want to manipulate more than one variable in an experiment? • to study multiple variables at once • we may have reason to believe that the effects of one variable on another are conditional upon a third variable. Example: It may be the case that whether or not people behave aggressively after viewing violent television depends on whether they’ve been provoked or threatened.

  3. Factorial Designs • Multiple independent variables • Factorial designs [# of levels]  [# of levels] IV#1 IV#2 Example: a 2  3 factorial design 2 levels of the first IV, “violent TV viewing” (e.g., watching violent TV and nonviolent TV) and 3 levels of second IV, “provocation” (e.g., 0 threats, 1 threat, 2 threats)

  4. Factorial Designs • Possible outcomes in a 2  2 design main effect: manipulating one of the IV’s produces a change in the DV in a 2  2 design, you can have 0, 1, or 2 main effects interaction: the effect of one IV on the DV is dependent on the other IV

  5. No main effect of A or B, no interaction Provocations Aggressive behavior (DV) This represents a situation in which the experimental manipulations have no effects on the dependent variable. Aggressive TV viewing

  6. Main effect of A, no main effect of B and no interaction Provocations Aggressive behavior (DV) Watching violent TV leads to increases in aggressive behavior. Aggressive TV viewing

  7. Main effect of B, no main effect of A and no interaction Provocations Aggressive behavior (DV) Being provoked leads to increases in aggressive behavior. Aggressive TV viewing

  8. Main effect of A and B, no interaction Provocations Aggressive behavior (DV) Watching violent TV leads to aggressive behavior. and Being provoked leads to increases in aggressive behavior. Aggressive TV viewing

  9. No main effect of A or B; interaction Provocations Aggressive behavior (DV) Whether people behave aggressively after watching violent TV depends on whether they’ve been provoked. If provoked, violent TV leads people to behave aggressively. If not provoked, violent TV leads people to behave less aggressively. Aggressive TV viewing

  10. Main effect of A, no main effect of B; interaction Provocations Aggressive behavior (DV) Watching violent TV leads to less aggressive behavior. and it depends. Watching violent TV leads people to behave less aggressively when they have not been provoked. Aggressive TV viewing

  11. Main effect of B, no main effect of A; interaction Provocations Aggressive behavior (DV) Being provoked leads to more aggressive behavior. and it depends. Being provoked leads to more aggressive behavior when watching violent TV. When not watching violent TV, provoked and non-provoked people are equally aggressive. Aggressive TV viewing

  12. Main effect of A and B; interaction Provocations Aggressive behavior (DV) Watching violent TV leads to more aggressive behavior. and Being provoked leads to increases in aggressive behavior. and it depends. In the absence of provocation, there is no effect of violent TV viewing on behavior. When provoked, watching violent TV leads people to behave more aggressively. Aggressive TV viewing

  13. Experimental Research • Between- and within-subjects designs between-subjects: different people are exposed to each level of the IV within-subjects: the same people exposed to each level of the IV • Mixed design: one factor is a between-subjects factor and the other is a within-subjects factor

  14. Pros and cons of different designs

  15. Counter-balancing t1 t2 t3 Person 1 T1 T2 T3 Person 2 T1 T3 T2 Person 3 T2 T1 T3 Person 4 T2 T3 T2 Person 5 T3 T1 T2 Person 6 T3 T2 T1 Counter-balancing helps to ensure that the specific test used (T1, T2, T3) is uncorrelated with order of presentation

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