What are the methods used to control extraneous factors?

Types of Variable > Extraneous Variable

What are Extraneous Variables?

Extraneous variables are any variables that you are not intentionally studying in your experiment or test. When you run an experiment, you’re looking to see if one variable (the independent variable) has an effect on another variable (the dependent variable). In an ideal world you’d run the experiment, check the results, and voila! Unfortunately…like many things in life…it’s a little more complicated that than. Other variables, perhaps ones that never crossed your mind, might influence the outcome of an experiment. These undesirable variables are called extraneous variables.

A simple example: you want to know if online learning increases student understanding of statistics. One group uses an online knowledge base to study, the other group uses a traditional text. Extraneous variables could include prior knowledge of statistics; you would have to make sure that group A roughly matched group B with prior knowledge before starting the study. Other extraneous variables could include amount of support in the home, socio-economic income, or temperature of the testing room.

Types of Extraneous Variables

1. Demand characteristics: environmental clues which tell the participant how to behave, like features in the surrounding or researcher’s non-verbal behavior.
2. Experimenter / Investigator Effects: where the researcher unintentionally affects the outcome by giving clues to the participants about how they should behave.
3. Participant variables, like prior knowledge, health status or any other individual characteristic that could affect the outcome.
4. Situational variables, like noise, lighting or temperature in the environment.

Confounding Extraneous Variable

One type of extraneous variable is called a confounding variable. Confounding variables directly affect how the independent variable acts on the dependent variable. It can muddle your results, leading you to think that there is cause and effect when in fact there is not. In the above example, a confounding variable could be introduced if the researcher gave the text book to students in a low income school, and assigned online learning to students in a higher income school. As students in higher income schools typically take more challenging coursework than students in lower income schools, pre-knowledge becomes a confounding extraneous variable.

Extraneous variables should be controlled if possible. One way to control extraneous variables is with random sampling. Random sampling does not eliminate any extraneous variable, it only ensures it is equal between all groups. If random sampling isn’t used, the effect that an extraneous variable can have on the study results become a lot more of a concern.

References

Beyer, W. H. CRC Standard Mathematical Tables, 31st ed. Boca Raton, FL: CRC Press, pp. 536 and 571, 2002.
Dodge, Y. (2008). The Concise Encyclopedia of Statistics. Springer.
Everitt, B. S.; Skrondal, A. (2010), The Cambridge Dictionary of Statistics, Cambridge University Press.
Kotz, S.; et al., eds. (2006), Encyclopedia of Statistical Sciences, Wiley.

---------------------------------------------------------------------------

Need help with a homework or test question? With Chegg Study, you can get step-by-step solutions to your questions from an expert in the field. Your first 30 minutes with a Chegg tutor is free!

Comments? Need to post a correction? Please Contact Us.

1. Experiments
2. Extraneous Variable

Extraneous Variable

By Dr. Saul McLeod, updated 2019

---

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

Anything that is not the independent variable that has the potential to affect the results is called an extraneous variable. It can be a natural characteristic of the participant, such as intelligence levels, gender, or age for example, or it could be a feature of the environment such as lighting or noise.

The researcher wants to make sure that it is the manipulation of the independent variable that has an effect on 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.

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

Demand characteristics are all the clues in an experiment which convey to the participant the purpose of the research. Demand characteristics can change the results of an experiment if participants change their behavior to conform to expectations.

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:

How to reference this article:

McLeod, S. A. (2019, July 30). Extraneous variable. Simply Psychology. www.simplypsychology.org/extraneous-variable.html

---

Home | About Us | Privacy Policy | Advertise | Contact Us

Simply Psychology's content is for informational and educational purposes only. Our website is not intended to be a substitute for professional medical advice, diagnosis, or treatment.

© Simply Scholar Ltd - All rights reserved

What method is the best for controlling extraneous variables?

What are the methods of extraneous variables?

Which of the following techniques are used to control extraneous variables in research?