Factorial Experiments Factorial Design = experiment in which more than one IV (factor) at a time is manipulated Uses all possible combinations of the levels.

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Presentation transcript:

Factorial Experiments Factorial Design = experiment in which more than one IV (factor) at a time is manipulated Uses all possible combinations of the levels of the factors The factors are “orthogonal”

Factorial Designs Main effects –The effect of each IV alone Interactions –When the effect on one variable depends on the level of another variable

Between-subjects factorial design –2 or more between-subjects factors (IVs) Within-subjects factorial design –2 or more within-subjects factors –Counterbalancing Mixed factorial design –1 or more of each (between-subjects and within-subjects factors) –Counterbalancing

Counterbalancing in Factorial Designs Necessary for order and sequence effects when there are within-subjects factors Define a counterbalancing variable –Calculate the number of conditions (the product of the number of levels for all within-subjects IVs) –Define the levels of the counterbalancing variable using a Latin Square or Balanced Latin Square –Assign subjects to counterbalancing groups using block randomization

Designing an Experiment Selecting Participants –convenience vs. random samples –Sample Size - rule of thumb: 20 per condition Manipulation of IV: straightforward vs. staged DV measures –Self-report vs. Behavioral –Floor and Ceiling effects Pilot testing Manipulation checks