by Saul McLeod published 2008

A variable is anything that can vary, i.e. changed or be changed, such as memory, attention, time taken to perform a task etc.

Variable are given a special names that only apply to experimental investigations. One is called the dependent variable and the other the independent variable.  In an experiment, the researcher is looking for the possible effect on the dependent variable that might be caused by changing the independent variable.

• Independent variable (IV): Variable the experimenter manipulates (i.e. changes) – assumed to have a direct effect on the dependent variable.

• Dependent variable (DV): Variable the experimenter measures, after making changes to the IV that are assumed to affect the DV.

For example, we might change the type of information (e.g. organized or random) given to participants to see what affect this might have on the amount of information remembered.

In this particular example the type of information is the independent variable (because it changes) and the amount of information remembered is the dependent variable (because this is being measured).

When we conduct experiments there are other variables that can affect our results, if we do not control them. 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 DV to change must be controlled. These other variables are called extraneous or confounding variables.

Extraneous Variables

Extraneous variables – These are all variables, which are not the independent variable, but could affect the results (e.g. DV) of the experiment.  Extraneous variables should be controlled were possible. They might be important enough to provide alternative explanations for the effects.

There are two 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.

2. Participant / Person variables – This refers to the ways in which each participant varies from the other, and how this could effect 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 affect their performance and the results of the experiment. The experimental design chosen can have an affect on participant variables.

Suppose I wanted to measure the effects of Alcohol (IV) on driving ability (DV) I 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 drove this make of car before.

• Familiarity with the test: Some people may do better than others because they know what to expect in 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 cite this article:

McLeod, S. A. (2008). . Retrieved from