Experimental Designs Show The Uniqueness of Experimental Methodology Experimental Control Determination of Causality Internal versus External Validity Another advantage of a well-designed experimental method is its high level of internal validity. A design that has high internal validity allows you to conclude that a particular variable is the direct cause of a particular outcome. In contrast external validity is often seen as a challenge for experimental work. External validity is the degree to which conclusions drawn from a particular set of results can be generalized to other samples and situations. The sample in a particular experiment may not represent the larger population of interest, and the experimental situation may not resemble the real-world context that it is designed to model because of its artificiality. The concern around artificiality is controversial and not shared by everyone who does psychological research. Key Constructs of Experimental Methods Independent and Dependent Variables Experimental
and Control Groups Placebo Effect Random Assignment Types of Experimental Designs Between-Subjects Designs Advantages of Between-Subjects Designs Disadvantages of
Between-Subjects Designs Within-Subjects Designs Advantages of Within-Subjects Designs Disadvantages of Within-Subjects Designs Matched Group Designs Advantages of Matched Group Designs Disadvantages of Matched Group Designs Confounding Factors and Extraneous Variables Participant Characteristics The Hawthorne Effect Demand Characteristics Other Confounds Strategies for Dealing with Confounds Hold Potential Confounding Variables Constant Vary Test Items and Tasks Use Blind and Double-Blind Designs Statistically Control for Variables that Can’t be
Experimentally Controlled Use Randomization and Counterbalancing Ceiling and Floor
Effects What Steele and Aronson Found Ethical Considerations in Experimental Design Placebo/Control Group and Denial of Treatment Confederates and Deceit In what study are both the researcher and the participants unaware of group assignments?A double-blind study withholds each subject's group assignment from both the participant and the researcher performing the experiment. If participants know which group they are assigned to, there is a risk that they might change their behavior in a way that would influence the results.
What is a doubleFor example, let's imagine that researchers are investigating the effects of a new drug. In a double-blind study, the researchers who interact with the participants would not know who was receiving the actual drug and who was receiving a placebo.
What is it called when participants are aware of the study?Subject bias, also known as participant bias, is a tendency of participants (subjects) in an experiment to consciously or subconsciously act in a way that they think the experimenter or researcher wants them to act. It often occurs when subjects realize or know the purpose of the study.
What is an example of a singleExample: Yogurt Tasting
The researchers know which yogurt containers are low-fat and which are high-fat, but participants are not told. This is an example of a single-blind study because the researchers know which participants are in the low- and high-fat groups but the participants do not know.
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