Extraneous Variables

Definition - In an experiment, any variable other than the IV that might potentially affect the DV.

Situational Variables - Those features of a research situation that may influence participants' behaviour and act as EVs.

Extraneous Variables

Demand Characteristics - A cue that makes P's aware of what the researcher excepts/how to behave. 

Investigator effects - The effect that researcher's expectations have on the P's.

Order effects - The order in which conditions are presented can cause fatigue or awareness of aims.

Time of day, temperature, noise - These environmental factors can affect performance of P's.

Participant Variables - Any characteristic of individual participants. These act as EV's only if an independent design is used. If a repeated measures design is used, these variables are controlled.

Age, intelligence, motivation, experience - Individual characteristics could affect performance.

Gender - This individual difference can affect results due to the way individuals have been socialised. 

Participant effects - May occur because participants actively seek cues about how to behave. 

Social Desirability - The tendency to answer questions in a way that presents them in a better light.

Hawthorne effect - P's alter behaviour because they know they are being observed.

How do Psychologists deal with participant effects?Single Blind - The participant doesn't know the true aims of the study. It prevents the participant from seeking cues about the aims and reacting to them. Experimental Realism - Make the experimental task sufficiently engaging so the participant pays attention to the task and not the fact that they are being observed.

How do psychologists deal with situational variables?Double Blind - Neither the participant nor the experimenter are aware of the important details and so they have no expectations. Standardised procedures - Ensure that all participants are tested under the same conditions (helps to control investigator/experimental effects).

Investigator/experimenter bias - The effect that an investigator/experimenter's expectations have on the participants and on the results of a research study.

!