Download - Within Subjects Designs
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Within Subjects Designs
• AKA Repeated Measures Design• Remember matched groups design?
– Allowed more power if you matched on correct variable
– Within Subjects Designs can be considered the ultimate way of matching.
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Reasons to use Within Subjects Designs
• 1. Requires fewer subjects• 2. Often more convenient or efficient
• ludwig and DeWitt (1993)
• 3. More sensitive (has more power)• Infant smiles
• 4. Sometimes the question requires a within Ss Design
• Learning studies – acquisition
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Issue to worry about with within Ss designs
• Progressive Error– Test person over and over again– Might get better
• Practice effects– Might get worse
• Fatigue effects
• Which threat to internal validity are we talking about?– Maturation
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Progressive Error
• Kahneman, Fredrickson, Schreiber, and Redelmeier (1993)– Pain Perception– Hypothesis
• It is the final moments of a painful episode that we remember the most.
• Duration of pain plays a smaller role
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Potential Design• Long trial
– Keep hand in 14 degree Celsius water for 60s• Then leave hand in for an additional 30 seconds while
temperature is raised 1 degree to 15 degrees• 7 minute break• Short trial
– Keep hand in 14 degree Celsius water for 60s• Asked participants which trial they would prefer to repeat
– 69% chose Long trial.• Supports notion that final moments are more memorable. (14
degrees vs 15 degrees)– IV? DV?– Any issues?
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Actual Design• Randomly assigned participant to one of two
balancing conditions• Half of Ss
– Long/break/Short 72% 28%
• Other half of Ss– Short/break/Long 33% 67%
• Collapse across balancing condition– 69% prefer long trial
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Balancing Progressive Error
• Subject x Subject Balancing– progressive error is balanced for each
participant– each participant experiences the conditions of
the experiment more than once, and in a different order each time
– Each person experiences a balanced presentation of conditions
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Balancing Progressive Error• Across Subjects Balancing
– progressive error is balanced across different participants
– Each participant only experiences each condition of the experiment one time.
– different participants experience different orders of conditions
– Thus, an individual participant would not be balanced, but after we average across participants the design would be balanced.
• Which balancing technique was used in the cold water (pain) experiment?– Subject x Subject or Across Subjects?
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Balancing Progressive Error
• Subject x Subject– Block Randomization– ABBA counterbalancing
• Across Subjects– Complete (All Possible Orders)– Partial Counterbalancing
• Latin Square• Systematic Sequential Rotation
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example of subject x subject balancing
• Sackheim, Gur, and Saucy (1978)– does one side of our face express more emotion?
• brain lateralization – left brain – right brain
» contralateral
– composite pictures• left composite• right composite• normal
– six emotions• happy, sad, surprise, fear, anger, and disgust
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Latin Square• 1) Randomly order the conditions of the
experiment – we will do a study with 6 conditions
• Let’s say 6 perfumes or colognes– Perfume and cologne A, B, C, D, E, F– F=1– C=2– B=3– E=4– A=5– D=6
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Latin Square• To generate the first order use the following rule
– 1, 2, N, 3, N-1, 4, N-2, 5, N-3, 6.........• N – refers to the number of conditions in the study
• With 6 conditions our rule would be– 1, 2, N, 3, N-1, 4
• So our first row (first order of conditions would be).– 1, 2, 6, 3, 5, 4 or F, C, D, B, A, E
• Now to generate the other conditions we simply add 1 to each column– 1, 2, 6, 3, 5, 4 or F, C, D, B, A, E– 2, 3, 1, 4, 6, 5 C, B, F, E, D, A– 3, 4, 2, 5, 1, 6 B, E, C, A, F, D– 4, 5, 3, 6, 2, 1 E, A, B, D, C, F– 5, 6, 4, 1, 3, 2 A, D, E, F, B, C– 6, 1, 5, 2, 4, 3 D, F, A, C, E, B
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Latin Square• Notice each condition occurs in each of the six possible positions (columns)
– F, C, D, B, A, E– C, B, F, E, D, A– B, E, C, A, F, D– E, A, B, D, C, F– A, D, E, F, B, C– D, F, A, C, E, B
• Also notice that each condition occurs after each of all of the other conditions
– F, C, D, B, A, E– C, B, F, E, D, A– B, E, C, A, F, D– E, A, B, D, C, F– A, D, E, F, B, C– D, F, A, C, E, B
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Systematic Sequential Rotation
• Randomly order the conditions– 1, 2, 3, 4, 5, 6 or F, C, B, A, E, D
• Now simply add 1 to each column until you have 6 rows– 1, 2, 3, 4, 5, 6 or F, C, B, A, E, D– 2, 3, 4, 5, 6, 1 or C, B, A, E, D, F– 3, 4, 5, 6, 1, 2 or B, A, E, D, F, C – 4, 5, 6, 1, 2, 3 or A, E, D, F, C, B– 5, 6, 1, 2, 3, 4 or E, D, F, C, B, A– 6, 1, 2, 3, 4, 5 or D, F, C, B, A, E
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Systematic Sequential Rotation• Notice each condition still occurs in each of the six possible conditions
– F, C, B, A, E, D– C, B, A, E, D, F– B, A, E, D, F, C – A, E, D, F, C, B– E, D, F, C, B, A– D, F, C, B, A, E
• However each condition is no longer preceded by each of the other conditions. It is always the same condition that precedes.
– F, C, B, A, E, D– C, B, A, E, D, F– B, A, E, D, F, C – A, E, D, F, C, B– E, D, F, C, B, A– D, F, C, B, A, E