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CHAPTER 6 Control Problems in Experimental Research

CHAPTER 6 Control Problems in Experimental Research. 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

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CHAPTER 6 Control Problems in Experimental Research

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  1. CHAPTER 6Control Problems in Experimental Research

  2. Chapter 6. Control Problems in Experimental ResearchChapter 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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.

  10. 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

  11. Problems with Biasing • Experimenter bias • Experimenter expectations can influence subject behavior • Controlling for experimenter bias • Automating the procedure • Using a double blind procedure

  12. 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

  13. 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

  14. Lab PrepStroop Effect • John Ridley Stroop (1935) 1 RED GREEN BLUE YELLOW 2 REDGREEN BLUEYELLOW 3

  15. Lab PrepStroop Effect • Modern-day Stroop Paradigm REDGREENBLUEYELLOW congruent REDGREENBLUEYELLOW incongruent Automaticity Relative Speed of Processing (“horse-race” model)

  16. “Horse-Race” Model When two processes occur in parallel, the faster one May interfere with the slower one, but not vice versa. RED “red”

  17. “Horse-Race” Model When two processes occur in parallel, the faster one May interfere with the slower one, but not vice versa. RED “red”

  18. 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.

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