Extraneous variables (A brief guide)

In this guide, we will discuss Extraneous variables, types of extraneous variables and examples, what are variables, extraneous variables, and confounding variables and we will mention some types of experimental designs to consider when doing research.

What are Extraneous variables?

Extraneous Variables are any of the variables that could affect the results of the experiment if the researcher(s) do not attempt to control them, where possible.

There are four types of extraneous variables:

  • Situational Variables: these are variables of the environment that can affect a participant’s behavior. Examples include noise, lightning, the temperature of the room, etc.
  • Participant/Person Variable: these variables can vary from one person to the other and can affect the participant’s performance and influence the results of the experiment. Such variables can include tiredness, having poor eyesight, being dyslexic, being hungry, using drugs, etc.
  • Experimenter/Investigator Effects: these variables can affect a participant’s behavior for instance, when the experimenter gives clues (unintentionally) about what the experiment is about or how they are expected to behave. 
  • Demand characteristics: these are the clues in an experiment that can give away the purpose of the research to the participants. Demand characteristics can affect the results of the experiment if the participants modify their behavior in order to conform to the expectations.
Extraneous variables (A brief guide)

Let’s take a look at an example. Let’s suppose we want to measure hours of sleep (IV) affects test results (DV) then we would need to consider extraneous variables so we minimize how the results are affected by them.

For instance, if the participant uses sleeping aids before a test, the level of anxiety, coffee consumption, method of study, etc.

Another example could be using an online learning method (IV) to increase the understanding of a subject such as statistics (DV).

We could have one group that learns with an online method and a second group that learns with a traditional statistics textbook.

Some of the extraneous variables that we could mention are the socio-economic background, time dedicated to studying, motivation, etc.

Subsequently, consider how such factors can potentially prevent you from finding the effect between the independent variable (manipulated) and the dependent variable (measured) in your research.

Extraneous variables, along with IV and DV are an important part of an experiment.

But before you start doing an experiment, you should deduce a directional hypothesis, out of which these IVs and DVs are produced.

Sources of Extraneous Variability

  • Task and instruction: when we talk about a task, we refer to what participants need to do so we can get the data to measure the dependent variable. The type of task we choose and the instructions can affect the results. For instance, if we need for the participant to press a key on the keyboard after a signal, we need to be clear about when to press it to avoid errors.
  • Testing effects: sometimes researchers find it necessary to do a pretest and posttest. If there are any differences that happen between the pretest and posttest, we can assume it is due to the treatment. However, it can also happen that the pretest can account for the results. This means there was something that happened when taking the pretest that affected the scores obtained on the posttest.
  • Experimenter expectancies: this can affect the participants’ performance. On occasion, if the behavior desired/expected by the experimenter is communicated to the participant, for instance, influencing the participant to choose the correct answer through visual or verbal cues.

What is a Variable?

It is important to understand what a variable is if it is not clear by now. A variable can be defined as a characteristic, property, or quantity that can vary and whose variation is susceptible to being measured.

Some examples of variables are motivation towards your job, learning of concepts, personality, etc. 

Moreover, Variables are applied to a group of people, animals, or objects that have the ability to acquire certain values according to the variable.

For instance, let’s consider how people can have different results when their IQ is tested and even more so, can be classified according to their score.

Other examples can be the effectiveness of a vaccine, time it takes for a disease to manifest, the productivity of a certain type of seed, etc. 

Extraneous variables (EV) and confounding variables (CV)

When reading through an experiment or research, there could be many extraneous variables that are obvious and others that are not so obvious.

However, when you want to consider some of the obvious variables that might become confound variables, answer two questions:

  • Is there academic evidence that the extraneous variables that you can identify, affect the DV?
  • Are there any logical (or practical) reasons to assume an EV may become a CV?

As indicated on Laerd dissertation, “When an extraneous variable changes systematically along with the variables that you are studying, this is called a confounding variable. A variable is considered to be confounding because it provides an alternative explanation for your results; that is, an alternative explanation for the relationship or differences between the variables and/or groups that you are measuring. This threatens the internal validity of your results.”

What is an experiment/study?

The term “experiment” can have at least two meanings, one general, and the other particular.  The general one refers to ‘taking action’ and then observing the consequences.

But we don’t specifically refer to the old fashioned meaning of ‘experimenting’ in the way we have learned, in a lab with a bunch of substances we mix, and then we observe the reaction.  

The essence relies on the intentional manipulation of variables to analyze the possible effects.

We could then elaborate on the meaning by saying a research study or experiment is where one or more independent variables are manipulated deliberately so we can analyze the effects or consequences of the manipulation over one or more dependent variables.

For example, if you were researching the possible effect of the content of certain antisocial television shows over the aggressive behavior of a group of children, you could set the experimental conditions as having one group watching a tv show with antisocial content and another group with prosocial content.

Subsequently, you could observe and measure which group displays higher rates of aggressive behavior.

Types of studies for user research

When we conduct research, the first thing is to establish a causal relationship between variables.

Usually, we would have three major types of studies:

  • Experimental study: one of the characteristics of an experimental study, is the random assignment of participants to different treatments. This can imply a better control over the influence of extraneous variables and a higher level of internal validity.
  • Quasi-experimental study: if you decide to conduct a study without random assignment of the participants, it would be a quasi-experimental design. However, this type of study also deliberately manipulates at least one independent variable to see the effect with one or more of the dependent variables.
  • Correlational study: here you examine the relationship between two variables (i.e. positive correlation). This type of study is characterized by being mainly descriptive.

Why is this blog about Extraneous variables important?

It is important to acknowledge the existence of extraneous variables since they can affect the outcome or the results of an experiment and also understand what a variable is.

We have talked about the possible types of extraneous variables to look out for when we have decided to do research or we have been asked to come up with an experimental design.

Subsequently, remember how in a study, you can have one or more variables, and considering the sources of extraneous variability we have talked about, so it can help to mitigate the effect or may let you control them.

Please feel free to leave any comments or thoughts about the content of this article!

Frequently Asked Questions (FAQs) about Extraneous variables

What is an extraneous variable in an experiment?

An extraneous variable or undesirable variable in an experiment are variables that are not intentionally included or being an object of study in such an experiment.

When performing an experiment, you are looking to study how the independent variable has an effect on the dependent variable. 

What is an extraneous variable in research with example?

An example of an extraneous variable in research could be aspects of the environment such as noise, lighting conditions, etc., or personal variables that can affect a participant’s behavior such as exhaustion, lack of sleep, hunger, etc. 

What are extraneous and confounding variables?

Extraneous variables are any factors that are not being studied but are part of the experiment and the confounding variables are those related to the independent variable that affects the dependent variable.

How can researchers control extraneous variables?

Random sampling is one way a researcher can control extraneous variables.

However, random sampling won’t eliminate any extraneous variable, it only makes sure to equal the ‘balance’ between groups of subjects.

What are 3 types of variables?

The 3 types of variables are: independent (manipulate), dependent (measure), and controlled. Consider how a variable can be any factor, trait, or condition that can exist in different amounts/types.


McLeod, S. (2019) Extraneous Variable. Retrieved from simplypsychology.org.

Stephanie Glen. “Extraneous Variable Simple Definition” From StatisticsHowTo.com: Elementary Statistics for the rest of us! Retrieved from statisticshowto.com.

Dissertation.laerd.com: “Extraneous and confounding variables”

Chapter 8. Sources of Extraneous Variability. Click here.