Simply Psychology Logo


Extraneous Variable

Extraneous Variable

By Saul McLeod, updated


When we conduct experiments there are other variables that can affect our results, if we do not control them.

Extraneous variables are all variables, which are not the independent variable, but could affect the results of the experiment.

The researcher wants to make sure that it is the manipulation of the independent variable that has changed the changes in the dependent variable.

Hence, all the other variables that could affect the dependent variable to change must be controlled. These other variables are called extraneous or confounding variables.

Extraneous variables should be controlled were possible, as they might be important enough to provide alternative explanations for the effects.

Independent, Dependent and Extraneous Variables

There are four types of extraneous variables:

1. Situational Variables

These are aspects of the environment that might affect the participant’s behavior, e.g. noise, temperature, lighting conditions, etc. Situational variables should be controlled so they are the same for all participants.

Standardized procedures are used to ensure that conditions are the same for all participants. This includes the use of standardized instructions

2. Participant / Person Variable

This refers to the ways in which each participant varies from the other, and how this could affect the results e.g. mood, intelligence, anxiety, nerves, concentration etc.

For example, if a participant that has performed a memory test was tired, dyslexic or had poor eyesight, this could effect their performance and the results of the experiment. The experimental design chosen can have an affect on participant variables.

Situational variables also include order effects that can be controlled using counterbalancing, such as giving half the participants condition 'A' first, while the other half get condition 'B' first. This prevents improvement due to practice, or poorer performance due to boredom.

Participant variables can be controlled using random allocation to the conditions of the independent variable.

3. Experimenter / Investigator Effects

The experimenter unconsciously conveys to participants how they should behave - this is called experimenter bias.

The experiment might do this by giving unintentional clues to the participants about what the experiment is about and how they expect them to behave. This affects the participants’ behavior.

The experimenter is often totally unaware of the influence which s/he is exerting and the cues may be very subtle but they may have an influence nevertheless.

Also, the personal attributes (e.g. age, gender, accent, manner etc.) of the experiment can affect the behavior of the participants.

4. Demand Characteristics

these are all the clues in an experiment which convey to the participant the purpose of the research.

Participants will be affected by: (i) their surroundings; (ii) the researcher’s characteristics; (iii) the researcher’s behavior (e.g. non-verbal communication), and (iv) their interpretation of what is going on in the situation.

Experimenters should attempt to minimize these factors by keeping the environment as natural as possible, carefully following standardized procedures. Finally, perhaps different experimenters should be used to see if they obtain similar results.

Suppose we wanted to measure the effects of Alcohol (IV) on driving ability (DV) we would have to try to ensure that extraneous variables did not affect the results. These variables could include:

• Familiarity with the car: Some people may drive better because they have driven this make of car before.

• Familiarity with the test: Some people may do better than others because they know what to expect on the test.

• Used to drinking. The effects of alcohol on some people may be less than on others because they are used to drinking.

• Full stomach. The effect of alcohol on some subjects may be less than on others because they have just had a big meal.

If these extraneous variables are not controlled they may become confounding variables, because they could go on to affect the results of the experiment.


How to reference this article:

McLeod, S. A. (2019, July 30). Extraneous variables. Retrieved from https://www.simplypsychology.org/extraneous-variable.html


Print Friendly and PDF

Home | About | A-Z Index | Privacy Policy | Contact Us

This workis licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 Unported License.

Company Registration no: 10521846