chapter 6 control problems in experimental research
TRANSCRIPT
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CHAPTER 6Control Problems in
Experimental Research
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Chapter 6. Control Problems in Experimental Research
Chapter Objectives
• Distinguish between-subjects designs from within-subjects designs
• Understand how random assignment can solve the equivalent groups problem in between-subjects designs
• Understand when matched random assignment should be used when attempting to create independent groups
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Chapter Objectives
• Distinguish between progressive and carry-over effects in within-subjects designs
• Describe the various forms of counterbalancing
• Describe the specific types of between- and within-subjects designs that occur in developmental psychology, and understand the problems associated with each
• Describe how participant/experimenter bias can occur and how it can be controlled
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Between-Subjects Designs
• Comparison is between two different groups of subjects (each subject receives one level of IV)
• Necessary when
• Subjects in each condition have to be naïve
• Barbara Helm study
• Subject variable (e.g., gender) is the IV
• Main problem to solve: creating equivalent groups
Level 1 Level 2
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Creating Equivalent Groups
• Random assignment• Each subject has equal chance of being assigned to any
group in the study • Spreads potential confounds equally through all groups• Accomplished through blocked random assignment
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Creating Equivalent Groups
• Random assignment• Each subject has equal chance of being assigned to any
group in the study • Spreads potential confounds equally through all groups• Accomplished through blocked random assignment
• Matching • Deliberate control over a potential confound• Use when• Small N per group might foil random assignment
• Some matching variable correlates with DV
• Measuring the matching variable is feasible
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Within-Subjects Designs
• Also called repeated-measures designs (same subjects in every level of an IV)
• Comparison is within the same group of subjects• Used when comparisons within the same individual are essential
(e.g., perception studies)
• Removes possibility that differences between levels of the IV due to individual differences
Level 1 Level 2
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Within-Subjects Designs
• Main problem to solve order effects• Progressive• Carry-over (harder to control)• Sequence A-B may yield differ carryover than the sequence
B-A
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Controlling Order Effects
• Counterbalancing• Altering the order of the experimental conditions
• Complete counterbalancing (all possible orders = x!)• Test participants in every possible different order at least
once• Works well with only a few conditions
• Partial counterbalancing• Random sample of all possible combinations is selected
Notice: Skip p219 “Testing more than once per condition” to end of p 223.
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Methodological Control in Developmental Research
• Cross-sectional design• Between-subjects design• Potential for cohort effects• Worse with large age differences
• Longitudinal design• Within-subjects design• Potential for attrition difficulties
• Cohort sequential design• Combines cross-sectional and longitudinal
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Problems with Biasing
• Experimenter bias• Experimenter expectations can influence subject
behavior
• Controlling for experimenter bias• Automating the procedure• Using a double blind procedure
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Problems with Biasing
• Subject bias• Hawthorne effect: Effect of knowing one is in a study• “Good” subjects• Participants tend to be cooperative, to please the researcher
• Evaluation apprehension• Participants tend to behave in ideal ways so as not to be evaluated
negatively
• Demand characteristics• Cues giving away true purpose and study’s hypothesis
• Controlling for participant bias• Effective deception• Use of manipulation checks• Field research
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Ethical Responsibilities of Participants
• Be responsible• Show up for scheduled appointments, or inform
research of cancellation
• Be cooperative• Behave professionally when participating in research
• Listen carefully• Ask questions if unsure of your rights or of what you are
asked to do
• Respect the researcher• Do not discuss study with others
• Be actively involved in debriefing• Help the researcher understand your experience
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Lab PrepStroop Effect
• John Ridley Stroop (1935)
RED GREEN BLUE YELLOW
RED GREEN BLUE YELLOW
1
2
3
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Lab PrepStroop Effect
• Modern-day Stroop Paradigm
RED GREEN BLUE YELLOW
congruent
incongruent
RED GREEN BLUE YELLOW
Automaticity
Relative Speed of Processing (“horse-race” model)
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“Horse-Race” ModelWhen two processes occur in parallel, the faster one May interfere with the slower one, but not vice versa.
RED
“red”
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“Horse-Race” ModelWhen two processes occur in parallel, the faster one May interfere with the slower one, but not vice versa.
RED
“red”
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Is the “Horse-Race” Model Supported?
Congruent Incongruent
Name color
Read word
What would the horse race model predict?
If prediction turns out to be true, we support the model.