Overview
This lecture explains four types of psychological experiments—laboratory, field, natural, and quasi—outlining their definitions, strengths, and weaknesses.
Laboratory Experiments
- Conducted in a controlled environment where the experimenter manages all variables except the independent variable (IV).
- Allow only the IV to change between conditions to measure its effect on the dependent variable (DV).
- High internal validity due to control over variables; can establish cause and effect.
- Highly replicable through standardized procedures.
- Weaknesses include low external validity (not like real life), low ecological validity, and tasks may lack mundane realism.
- Participants might show demand characteristics, altering behavior because they know they're in an experiment.
Field Experiments
- Conducted in real-world settings (e.g., shopping centers, schools).
- Increased external and ecological validity due to natural environment and realistic tasks.
- Participants may be unaware of the study, reducing demand characteristics.
- Weaknesses include less control over variables (extraneous variables) and difficulty with random assignment, reducing internal validity.
Natural Experiments
- The IV occurs naturally; researchers do not manipulate it.
- Enables research in areas where manipulation is unethical or impractical.
- High external validity; behaviors occur as they would in real life and are free from demand characteristics.
- Researcher has no control over variables or group assignment, so internal validity is reduced and causality is hard to establish.
- Rare situations limit replicability.
Quasi Experiments
- No random assignment; groups are based on pre-existing characteristics (e.g., gender, age, clinical status).
- Only possible way to study some variables that cannot be manipulated.
- Differences between groups may be caused by confounding variables, which cannot be controlled.
Key Terms & Definitions
- Independent Variable (IV) — the factor manipulated by the experimenter.
- Dependent Variable (DV) — the factor measured to assess the effect of the IV.
- Internal Validity — degree to which a study demonstrates cause and effect.
- External Validity — extent to which findings generalize to real-world settings.
- Ecological Validity — similarity between experimental and real-world conditions.
- Mundane Realism — how typical the experimental task is compared to real life.
- Demand Characteristics — cues that influence participants' behavior.
- Extraneous Variables — any variable other than the IV that may affect the DV.
- Confounding Variables — variables that change with the IV and may affect results.
Action Items / Next Steps
- Review notes on types of experiments and their strengths/weaknesses.
- Watch follow-up videos for detailed examples and exam tips.
- Prepare worksheet/notes as suggested in the lecture.