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Chapter 7

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Nussbaum D

CHAPTER 7 Multifactorial experiments  Vary two or more independent variables  Provide direct tests of the main effects of each independent variable and the interaction effects between the independent variables The variables have two or more levels and can be within- or between- subjects.  Two independent variables can be added to a study as long as they are qualitatively different A multifactorial experiment is a more economical and efficient design to evaluate and test separate/joint influences of one or more independent variables. Notations and Terms Simplest multifactorial design has two independent variables, each with two levels/values. 2x2 factorial design  two independent variables, with each having two levels 3x4 factorial design  two independent variables, one with three levels and one with four.  AxA  the amount of „A‟ tells you how many independent variables  A xA  „A ‟ tells you how many levels the first IV has while „A ‟ tells you how many levels the second IV has With the designs, the values of each independent variable is multiplied by the other, as each value from one interacts with the values from the other.  In a 3x4 design, this means that there are 12 levels Theory and Experimentation Theory  How experiment is designed  How independent variables are developed and manipulated  How dependent variables are measured  What specific hypothesis are tested Very important in multifactorial designs as there are more variables to manipulate Example of Within-Subjects Experiment Adam and Kleck (2003) According to their theory, eye-gaze direction and facial expressions can be understood in terms of approach-avoidance motivation  Both work to share information such signals of approach/instigating behaviour AND fuel avoidance/trigger inhibition Constructed the theory of social signaling system: facial expressions and eye-gaze work as a way to govern approach and avoidance. They found that the amygdala seemed to be especially sensitive to fearful white eyes but not happy white eyes Devising Independent Variables Formulated hypothesis  Anger faces with direct gaze would be more readily perceived than anger faces with averted gaze  Fear faces with averted gaze would be more readily perceived than fear faces with direct gaze Researchers had to create experimental stimuli: materials that are used in constructing an independent variable  They create facial expressions in Photoshop o Anger with direct gaze o Anger with averted gaze o Fear with direct gaze o Fear with averted gaze Had to organize experimental task: task that participants performed that is used as an independent variable  Participants had to view faces on screen and decide what expression was being made Within-subject design was chosen because individual differences could be important in the processing emotions – people vary in their responses to different emotions  Also, is more economical Main Effects Def.: The effects of each independent variable on the dependent variable. Can be calculated for each independent variable.  Row means  the averages across levels of one independent variable  Column means  the averages across levels of the other independent variable Interactions Def.: When the effects of one level of the independent variable depend on the particular level of the other independent variable  Example (from study): on one hand, direct gaze led to faster judgement of anger faces but slower judgement of fear faces. On the other hand, averted gaze led to faster judgement of fear faces but slower judgement of anger faces. If an interaction exists, values will differ across levels of the independent variables (additional info from lecture) Interpreting the Results Steps to Interpreting results from multifactorial 2x2
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