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Extraneous variables are all variables, which are not the independent variable and could affect the results of the experiment (McLeod, S.A. 2018). Extraneous variables can be further categorized by situational variables, participant/person variable, experimenter/investigator effects and demand characteristics. In order to maintain an extraneous free experiment, standardized procedures are used to provide the same conditions for all participants. Random allocation to the conditions allows experimenters to control the participant variables (McLeod, S.A. 2018). Experimenter/investigator effect is more difficult to detect; as a person may be totally unaware of their influence on another such as personal attributes. Any clues which may guide the participants to the purpose of the experiment would create demand characteristic. Although the environment should be controlled it is important to keep the environment as natural as possible and maintain standardized procedures. In many experiments there are several investigators which monitor the environment, participants and other investigators to help identify any extraneous variables which may alter the results.
McLeod, S. A. (2018, Aug 10). Independent, dependent and extraneous variables. Retrieved from https://www.simplypsychology.org/variables.html