Research Methods

Experiment: an investigation looking for a casual relationship in which an independent variable is manipulated and is expected to be responsible for changes in the dependent variable.

Independent variable: the factor under investigation in an experiment which is manipulated to create two or more conditions and is expected to be responsible for changes in the dependent variable.

Dependent variable: the factor in an experiment which is measured and is expected to change under the influence of the independent variable.

Extraneous variable: a variable which either acts randomly affecting the DV in all levels of the IV or systematically.

Experimental condition: one or more of the situations in an experiment which represent different levels of the IV and are compared (or compared to a control condition).

Control condition: a level of the IV in an experiment for which the IV is absent. It is compared to one or more experimental conditions.

Experimental design: the way in which participants are allocated to levels of the IV.

Independent measures design: an experimental design in which a different group of participants is used for each level of the IV.

Strengths

Weaknesses

Different participants are used in each level of the IV so there are no order effects.

Participant variable can distort results if there are important individual differences between participants in different levels of the IV.

Participants see only one level of the IV, reducing the effect of demand characteristics.

More participants are needed than in a repeated measures design so the study may be less ethical if participants are harmed and less effective if there is a small sample because participants are hard to find.

Random allocation to levels of the IV can reduce effects of individual differences.

Repeated measures design: an experimental design in which each participant performs in each level of the IV.

Strengths

Weaknesses

Participant variables are unlikely to distort the effect of the IV, as each participant does all levels.

As participants see the experimental task more than once, they have greater exposure to demand characteristics.

Counterbalancing reduced order effects.

Order effects distort results

Uses fewer participants than independent measures so is good when participants are hard to find or at risk.

Matched pairs design: an experimental design in which participants are arranged into pairs. Each pair is similar in ways that are important to the study and one member of each pair performs in a different level of the IV.

Strengths

Participants see only one level on the IV, reducing the effect of demand characteristics.

Participant variables are less likely to distort the effect of the IV than in an independent measures design as individual difference are matched.

No order effects.

Demand characteristics: features of the experimental situation which give away the sims. They can cause participants to try to change their behavior.

Random allocation: a way to reduce the effect of confounding variable such as individual differences. Participants are put in…