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Experimental Designs

Experimental Designs. Experiments are conducted to identify how independent variables influence some change in a dependent variable. Researcher-Related Threats to Internal Validity. Experimenter Effect Observer Bias Researcher Attribute Effect.

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Experimental Designs

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  1. Experimental Designs

  2. Experiments are conducted to identify how independent variables influence some change in a dependent variable.

  3. Researcher-Related Threats to Internal Validity • Experimenter Effect • Observer Bias • Researcher Attribute Effect

  4. Participant-Related Threats to Internal Validity • The Hawthorne Effect • Testing Effect • Maturation • Experimental Mortality • Selection Biases • Intersubject Biases • Compensatory Study • Demoralization

  5. Procedure-Related Threats to Internal Validity • History • Instrumentation • Treatment Confound • Statistical Regression • Compensation

  6. Exercising Control • Creating Equivalent Groups (Treatment & Control) • Manipulating an Independent Variable • Controlling for extraneous variables

  7. Types of Experimental Designs • Pre-Experimental Design • Quasi-Experimental Design • “True” or Classical Experimental Design

  8. Pre-Experiments • Little control exercised by researcher • Conditions are not randomly assigned • Independent variable is either manipulated or observed • Types of Designs: • One-Shot Case Study • One-Group Pretest-Posttest Design • Static-Group Comparison

  9. Quasi-Experiments • Some Control exerted by researcher • Groups not randomly assigned -- assigned by pretest or natural categories – called “matching” • Independent variable is often observed in its naturally occurring context • Tend to be field experiments • Types of Designs: • Time-Series Designs • Nonequivalent Control Group Design • Multiple Time-Series Design

  10. True or Classical Experiments • Most controlled design • Must have random assignment to groups • Laboratory experiment • Independent variable is manipulated • Double-Blind Experiment is when the participants and those who have contact with the participants are unaware of the group to which a participant is assigned. • Manipulation checks are used to ensure the operationalization of the independent variable was manipulated as intended.

  11. Types of Classical Experiments • Pretest – Posttest Control Group Design • Posttest – Only Control Group Design • Solomon Four – Group Design

  12. Factorial Designs • Used when there is more than one independent variable • Examines complex causal relationships • how each independent variable affects the dependent variable (main effects) and how the independent variables combined affect the dependent variable (interaction effects)

  13. RQ: How does the sex of the speaker and immediacy influence perceived credibility? High Immediacy Moderate Immediacy Low Immediacy Female Speaker Male Speaker 2 x 3 Factorial Design

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