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Multiple Independent Variables

18 November, 2015 - 17:39

LEARNING OBJECTIVES

  1. Explain why researchers often include multiple independent variables in their studies.
  2. Define factorial design, and use a factorial design table to represent and interpret simple factorial designs.
  3. Distinguish between main effects and interactions, and recognize and give examples of each.
  4. Sketch and interpret bar graphs and line graphs showing the results of studies with simple factorial designs.

Just as it is common for studies in psychology to include multiple dependent variables, it is also common for them to include multiple independent variables. Schnall and her colleagues studied the effect of both disgust and private body consciousness in the same study. Researchers’ inclusion of multiple independent variables in one experiment is further illustrated by the following actual titles from various professional journals:

  • The Effects of Temporal Delay and Orientation on Haptic Object Recognition
  • Opening Closed Minds: The Combined Effects of Intergroup Contact and Need for Closure on Prejudice
  • Effects of Expectancies and Coping on Pain-Induced Intentions to Smoke
  • The Effect of Age and Divided Attention on Spontaneous Recognition
  • The Effects of Reduced Food Size and Package Size on the Consumption Behavior of Restrained and Unrestrained Eaters

Just as including multiple dependent variables in the same experiment allows one to answer more research questions, so too does including multiple independent variables in the same experiment. For example, instead of conducting one study on the effect of disgust on moral judgment and another on the effect of private body consciousness on moral judgment, Schnall and colleagues were able to conduct one study that addressed both questions. But including multiple independent variables also allows the researcher to answer questions about whether the effect of one independent variable depends on the level of another. This is referred to as an interaction between the independent variables. Schnall and her colleagues, for example, observed an interaction between disgust and private body consciousness because the effect of disgust depended on whether participants were high or low in private body consciousness. As we will see, interactions are often among the most interesting results in psychological research.