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This informative guide explores various types of experimental designs and common threats to internal validity in research studies. It discusses researcher-related, participant-related, and procedure-related threats, as well as different types of experimental designs such as pre-experiments, quasi-experiments, and true experiments. The text includes insights on controlling variables, creating equivalent groups, manipulating independent variables, and conducting classical experiments. It also delves into factorial designs and their significance in examining complex causal relationships. Moreover, the text addresses the importance of manipulation checks and the implementation of double-blind experiments in ensuring research credibility. The guide concludes by posing a research question related to the influence of speaker sex and immediacy on perceived credibility, introducing a 2x3 factorial design.
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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
Participant-Related Threats to Internal Validity • The Hawthorne Effect • Testing Effect • Maturation • Experimental Mortality • Selection Biases • Intersubject Biases • Compensatory Study • Demoralization
Procedure-Related Threats to Internal Validity • History • Instrumentation • Treatment Confound • Statistical Regression • Compensation
Exercising Control • Creating Equivalent Groups (Treatment & Control) • Manipulating an Independent Variable • Controlling for extraneous variables
Types of Experimental Designs • Pre-Experimental Design • Quasi-Experimental Design • “True” or Classical Experimental Design
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
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
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.
Types of Classical Experiments • Pretest – Posttest Control Group Design • Posttest – Only Control Group Design • Solomon Four – Group Design
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)
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
