Overview
This lecture explains the experimental method in psychology, focusing on how manipulation and random assignment allow researchers to determine causal relationships.
Limitations of Correlational Research
- Correlational research cannot establish causation due to possible third variables influencing the relationship.
- The third variable problem refers to unmeasured factors that could explain an observed correlation.
Experimental Method: Manipulation
- The experimental method solves the third variable problem by manipulating one variable (the independent variable).
- Manipulation involves the researcher determining group assignments, removing ambiguity about what causes the outcome.
Groups in Experiments
- Participants are split into an experimental group (receives treatment) and a control group (does not receive treatment).
- Placebo treatments may be given to control groups to ensure participants' expectations do not influence results.
Random Assignment
- Random assignment (or allocation) is used to place participants into groups by chance.
- This avoids self-selection, where participants choose their groups, potentially introducing bias.
- Random assignment also prevents researcher bias in assigning participants to groups.
Variables in Experiments
- The independent variable is the manipulated variable, intended to be independent of other factors.
- The dependent variable is the outcome measured after manipulation to evaluate the effect of the independent variable.
Importance of Manipulation and Random Assignment
- Manipulation allows researchers to test if changing one variable causes a change in another.
- Random assignment is crucial to eliminate third variable problems and bias, supporting causal conclusions.
Key Terms & Definitions
- Third Variable Problem — When an unmeasured factor is responsible for an observed correlation.
- Manipulation — The researcher’s control over a variable in an experiment.
- Experimental Group — Participants receiving the treatment or manipulation.
- Control Group — Participants not receiving the treatment; used as a comparison.
- Placebo — A fake treatment given to control group participants to mimic the experience of the experimental group.
- Random Assignment (Random Allocation) — Placing participants into groups by chance to avoid bias.
- Independent Variable — The variable manipulated by the researcher.
- Dependent Variable — The variable measured to assess the effect of the manipulation.
Action Items / Next Steps
- Review the differences between experimental and correlational methods.
- Practice identifying independent and dependent variables in example experiments.