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Chapter 8

Chapter 8. Experimental Designs: Between-Subjects Design. Experimental Strategy. Basic Characteristics: Manipulation of variable to create two or more levels Measurement of second variable Comparison of scores between levels Control of other variables. BGD.

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Chapter 8

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  1. Chapter 8 Experimental Designs: Between-Subjects Design

  2. Experimental Strategy • Basic Characteristics: • Manipulation of variable to create two or more levels • Measurement of second variable • Comparison of scores between levels • Control of other variables

  3. BGD • Compares diff groups of individuals • Scores / groups are independent

  4. Advantages & Disadvantages • Advantages • Independent scores • Scores not contaminated • No practice, fatigue • No drug carry-over • Disadvantages • Large number of participants • Individual diff • Gender • History • High variability in scores

  5. BGD Confounds • Assignment Bias-confounding from ind. Diff. • Environmental var-any environ factors that diff between groups • Room • Temperature • Time of day

  6. Techniques for Equivalent Groups • Process to obtain participants should be similar • Treated equally • Characteristics of one group similar as possible • Restricted random assignment • Matching

  7. Matching • Assigning individuals to groups to balance potential confound • Can be tedious / time

  8. Variability • Can obscure effects of treatment • Variancestatistical measure that measures differences between scores • Example how ind diff influence variance and how variance influence interpretation of results

  9. Two Populations A & B

  10. Variance within the groups is bad • Variance between groups is good • Goal: maximize difference between conditions and minimize difference within the conditions • Minimize WGV: standardize process, limit ind diff, random assgn, matching, increase N

  11. Two-Group Design • Two levels of IV • Experimental Group • Control Group • Simplicity and maximizes effect of IV • Problem: true nature of relationship between IV and DV incomplete

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