Psych 218 Introduction to Behavioral Research Methods

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Psych 218Introduction to Behavioral Research
Methods

• Week 10 Lecture 19

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Outline of Todays Lecture

• Last lecture we discussed
• Manipulating variables between-subjects vs.
  within-subjects
• Research using Multiple factors (independent
  variables)
• Today we will discuss
• Research using Multiple factors (independent
  variables)

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Factorial Research Designs

• Used to assess the effects of 2 or more
  independent variables (factors) on your dependent
  variable
• Using multiple IVs in one experiment is
• more economical (particularly for within-Ss)
• provides more information
• Main effects of each IV (separate effects of each
  IV)
• Interaction between the IVs (synergism) effect
  of one variable changes across the levels of the
  other variable

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Factorial Research Designs Possible Outcomes of
a 2 x2 Design

• No effects Main Effect A Only Main Effect
  B Only

B1, B2
B2
DV
DV
DV
B1, B2
B1
A1
A2
A1
A2
A1
A2
Factor A
Factor A
Factor A
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Factorial Research Designs Possible Outcomes of
a 2 x2 Design
Main Effects for A and B, No Interaction
Main Effects for A and B, Interaction (ordinal)
Main Effect for A only, Interaction (disordinal)
Main Effect for B only, Interaction (ordinal)
B2
B2
B2
B2
B1
B1
DV
DV
DV
DV
B1
B1
A1
A2
A1
A2
A1
A2
A1
A2
Factor A
Factor A
Factor A
Factor A
IMPORTANT always interpret the highest order
effect or interaction
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Example Factorial Experiment Perceiving Heading

• An experiment on perceiving the heading direction
  during steering control vs. riding and pointing

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Example Factorial Experiment Perceiving Heading

• IV1 observers task
• Steering control Steer so that you appear to be
  moving straight ahead
• Pointing Point in the direction towards which
  you perceive yourself to be moving while riding
• IV2 simulated velocity of observer movement
• Three levels 50, 100, and 200 ms-1
• Dependent Variable (measure) RMS
  (root-mean-squared) heading error

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Results

• Significant Effects
• Task Main Effect
• Interaction
  between task and velocity
• IMPORTANT! ALWAYS INTERPRET HIGHEST ORDER EFFECT

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Combining Between-Subjects and Within Subjects
Designs

• The Mixed Design
• Also known as split plot
• Groups of subjects each receive a unique level of
  the between Ss variable(s) and all levels of the
  within Ss variable(s)

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Three-factor Factorial Design Adding
Presentation Order as a Factor to Account for
Differential Carryover
Presentation order Variable (between) Group A
(control then pointing) Group B (pointing then
control) Found 3-way interaction that indicates
differential carryover (asymmetrical transfer)