Research Methods and Experimental Design
11. Experimental Design and Methodology
The Scientific Method in Psychology
Rigorous psychological research relies on robust experimental design to infer causality. While correlational studies can identify relationships between variables, only true experiments—characterized by random assignment and manipulation of an independent variable—can establish cause and effect.
Experimental Designs
Between-Subjects Design
- Different participants are assigned to each condition.
- Avoids carryover effects (like practice or fatigue).
- Requires more participants and is subject to individual differences.
Within-Subjects Design
- The same participants experience all conditions.
- Requires fewer participants and controls for individual differences.
- Subject to order effects, requiring counterbalancing.
The Hypothetico-Deductive Method
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1
Formulate a falsifiable hypothesis based on theory.
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2
Design an empirical study to test the hypothesis.
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3
Collect and analyze the data.
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4
Accept or reject the null hypothesis.
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5
Refine the theory based on findings.
Which type of validity refers to the extent to which the results of a study can be generalized to other situations, populations, or times?
External validity is about generalizability, whereas internal validity focuses on whether the study design properly establishes a causal relationship.
Correct answer: External Validity
Controlling for Bias
Researchers must rigorously control for extraneous variables that could become confounding variables. Confounders provide alternative explanations for the results, threatening internal validity. Strategies include randomization, blinding, and standardization of procedures.
Types of Variables
| Variable Type | Definition | Example in a Drug Trial |
|---|---|---|
| Independent Variable (IV) | The variable manipulated by the researcher. | Drug dosage (Placebo vs. 50mg) |
| Dependent Variable (DV) | The variable measured to assess the effect. | Reduction in depression scores |
| Confounding Variable | An uncontrolled variable that affects the DV. | Patients' concurrent psychotherapy |
What type of experimental setup ensures that neither the participants nor the experimenters interacting with them know who is receiving a particular treatment?
A double-blind procedure is essential to prevent both placebo effects in participants and experimenter expectancy effects.
Correct answer: Double-blind