Experiments

EXPERIMENTS

The Experimental Method

- Aims are stated.

- There are 2 or more levels of the independent variable (IV) manipulated by the experimenter.

- The effect is measured on a dependent variable (DV), which is operationalised.

- Extraneous variables are controlled and procedures are standardised.

- The hypothesis states the relationship between the IV and the DV.

- Causal conclusions can be drawn.

Control of Variables

- Confounding variables vary systematically with the IV, therefore any change in the DV may be due to a confounding variable instead of the IV.

- Extraneous variables are nuisance variables, and make it harder to detect changes in the DV.

- Mundane realism is the extent to which features of a study mirror the real world.

- Generalisation: findings from a study may lack generalisability if the materials or environment lack mundane realism, or if participants know they're being studied.

- Validity = legitimacy, genuineness.

Internal validity - enhanced by control of confounding variables and high mundane realism.

External validity - refers to the generalising to other situations (ecological validity), people (population validity) and historical periods (historical validity).

Hypotheses and Things

- Directional hypothesis states more, less, higher, lower, etc...

- Non-directional hypothesis does not state direction of difference.

- State direction if indicated by past research.

- Pilot study is a trial run with similar participant to test procedures, and change if necessary.

- Confederates are directed by a researcher to play certain roles in a study.

More Problems with Experiments

Demand characteristics - cues in an experimental situation that convey hypothesis to participants, creating expectations about how to behave.

Investigator effects - the unconscious cues from the investigator that affect participant's performance, other than what was intended, including indirect effects (e.g. investigator experimental design effect)

- Single blind or double blind (minimise these problems)

Experimental Design

Repeated measures - each participant is tested twice, to experience both levels of the IV.

Independent groups - each participant only being tested on 1 level of the IV.

Matched pairs - each participant is paired with another participant, and each pair receives both levels of the IV.​​​​​​

​​​​Counterbalancing - each condition is tested first or second in equal amounts (could be AB, BA or ABBA)

Evaluation

Repeated measures - involves order effects (e.g. practice or boredom) and guessing aims of the study, which can counterbalance.

Independent groups - participant variables are not controlled, may need more participants, but can use random allocation.

Matched pairs - matching takes time, and may not account for all variables that matter.

Laboratory and Field Experiments

Laboratory experiment - study with an IV and DV, conducted in a controlled environment.

Field experiment - study with an IV and DV, but conducted in a more natural environment.

- In both kinds of experiment, the IV may be contrived, therefore reducing mundane realism.

​​​​​​Evaluation

Laboratory experiment - participants are less likely to behave as they do in everyday life because of awareness of being studies, and contrived materials and environment.

Field experiment - environment more natural and awareness of being studied unlikely, therefore higher ecological validity but material may be contrived, reducing ecological validity. Ethical issues if debriefing is not possible.

Natural and Quasi-Experiments

Natural experiment - the IV is natural insofar as it varies whether or not the researcher is there. The DV may be measured in a lab.

Quasi-experiment - the IV is not a variable, but it is a condition that exists (e.g. age or having an external locus of control)

Evaluation

- In both natural and quasi-experiments, causal conclusions cannot be draw because: the IV is not deliberately changed, there is no random allocation (which controls confounding variables) and they may be unique characteristics of the participants.

- Participants may be aware of being studied, therefore reducing internal validity.

- The DV may be a fairly artificial task, reducing ecological validity.