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Study Notes

Control of Extraneous Variables

AS, A-Level
AQA, Edexcel, OCR, IB

Last updated 22 Mar 2021

Extraneous variables are unwanted factors in a study that, if not accounted for, could negatively affect (i.e. confound) the data subsequently collected.

Such factors potentially prevent researchers from finding a direct causal effect between the manipulated independent variables (IVs) and measured dependent variables (DVs) set out in an investigation.

For researchers to be confident that change in the IV will solely affect change in the DV, potential confounds need to be identified and controlled/eliminated; poor control will lead to results with lower reliability.

There are three key considerations to take when controlling extraneous variables:

Participant variables – minimizing differences between participants (e.g. their stage of development such as age, or ability such as IQ).

Researcher variables – factors such as researcher behaviour, appearance or gender could affect participant responses, so should be made consistent throughout the experiment.

Situational variables – control of the setting where the experiment takes place, such as keeping light, sound and temperature levels consistent.

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