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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
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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