Overview
This lecture introduces the main types of experiments in psychological research—laboratory, field, natural, and quasi-experiments—explaining their strengths and weaknesses.
Laboratory Experiments
- Laboratory experiments are conducted in controlled environments where the researcher controls all variables except the independent variable (IV).
- The researcher manipulates the IV to measure its effect on the dependent variable (DV).
- High control leads to high internal validity, allowing for cause-and-effect conclusions.
- Results are easy to replicate due to standardized procedures.
- Weaknesses include low external validity and low ecological validity, as lab settings and tasks may not reflect real life.
- Participants may show demand characteristics, altering their behavior because they know they are being studied.
Field Experiments
- Field experiments take place in real-world settings like schools or workplaces.
- Behavior is more natural, increasing external validity and ecological validity.
- Real-world tasks improve mundane realism, and participants may be unaware they're in a study, reducing demand characteristics.
- Less control over variables and inability to randomly assign participants decreases internal validity.
- Extraneous variables may affect results.
Natural Experiments
- In natural experiments, the IV occurs naturally; researchers do not manipulate it.
- Useful for studying effects that cannot be ethically or practically manipulated (e.g., effects of early deprivation).
- High external validity, as changes occur in real-life settings without researcher intervention.
- No control over variable assignment or extraneous variables, so cause and effect is less certain.
- Rare situations limit replication.
Quasi-Experiments
- Quasi-experiments study groups based on existing traits (e.g., gender, age) without random assignment.
- The only method to study certain variables that cannot be manipulated.
- Confounding variables may affect results, as group differences may exist beyond the studied factor.
Key Terms & Definitions
- Independent Variable (IV) — the factor that is manipulated in an experiment.
- Dependent Variable (DV) — the outcome measured in response to changes in the IV.
- Internal Validity — the degree to which the study shows a true cause-and-effect relationship.
- External Validity — how well results generalize to real-world settings.
- Ecological Validity — the extent to which findings reflect real-life situations.
- Mundane Realism — similarity of experimental tasks to real-world activities.
- Demand Characteristics — participants' altered behavior due to awareness of being studied.
- Extraneous Variables — other variables that might influence the DV.
- Confounding Variables — uncontrolled factors that systematically vary with the IV.
Action Items / Next Steps
- Review the four types of experiments and their strengths and weaknesses.
- Learn key terminology and definitions.
- Watch the next video on observational research methods.