Factorial Experiments Factorial Design experiment in which more

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 withinsubjects 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