Extraneous Variable (A Comprehensive Guide)

Extraneous Variables are those variables that cannot be controlled by the experimenter and also have a serious influence on the result of the experiment.

The foremost four extraneous variables that can disturb the findings are described below.

Extraneous variables have to be assessed in various areas of experimentation.

While developing the concept for research and assessing the finding of collected data.

Although, some extraneous variables are easy to predict which can be handled by the implementation of various techniques most of them abruptly interrupt in the research.

Different reasons for extraneous variables are able to be classified in three different domains such as

·         Participants

·         Experimenter

·         Procedure of research

Participants as a Source of Extraneous Variability

To avoid the extraneous variables that may cause by the participants we must focus on the listed things to avoid such problems


 History plays an important role in research especially in the administration of various measures to know about the progress and drawbacks during the start and end of the research it is known as pre and post assessment any happening during this period directly affect the dependent variable such as displaying in front of a group of children a violent TV program also notice their performance in a recess which were aggressive.

Then again display a nonviolent Programme the next week and notice their behavior which was comparatively less aggressive from the previous observation.

During this time period school administration takes a decision to replace the director of the school.

The new one is quite strict and disciplined.

Which interrupt our finding because we are unable to decide whether the change in behavior is due to the nonviolent Programme (Independent) or extraneous variable (principle)


 Maturation includes the developmental factors that are based on time such as physical growth, tiredness, and getting old.

These factors are not considered alarming ones but it can affect the behavior of a participant and affect the performance of independent variable such as considering the above example the extraneous variable could be that the children may get bored and feel irritated that they have to stay in the same room and watching a 2 hours long program that causes aggressive behavior rather than the TV show. 

Extraneous Variable (A Comprehensive Guide)


 The extraneous variable of attrition occurs when the participant loses in the experiment due to many reasons such as illness, feels bored, dies due to some reason, or consciously withdraws themselves.

In these conditions, the comparison is difficult to make because the new participant may don’t have similar characteristics like the previous ones

Demand Characteristics and evaluation apprehension

 People’s behavior is different from each other such as the behavior of people gathered in church, football games, in professional settings, and at home.

Variations in the environment in which the study is conducted sometimes provide the sign to the participant related to the research and what experimentation expecting from them as a result such as the extraneous variables would be the experimenter’s body language may reveal a lot and have a direct effect on the participant’s behavior.

People perform well when they know that they are the part of the study and being evaluated also give their best and sometimes act fake so that experimenter perceive them as a positive one known as evaluation apprehension  

Diffusion of Treatment

This extraneous variable is associated with something which is not under the control of the investigator such as when the researcher selects the population through purposeful sampling and marks the essential population for the experiment but at the same time the targeted population has some difference i.e. participants’ health, previous knowledge affect the findings.

If a participant which is selected through purposeful sampling but he already knows about the Milgram experiment works as an extraneous variable in this condition.

Experimenter as a Source of Extraneous Variability

To avoid the extraneous variables that may cause by the experimenters we must focus on the listed things to avoid such problems

Experimenter Characteristics

The character of the experimenter is considered the important one and also the major reason of extraneous variables such as experimenters way of dealing the participants, dressing style, gender, age, not prepare enough for the research also making jokes with the participants increase the chance of attrition, demand characteristics, and evaluation apprehension

Experimenter Bias

Two types of experimental Bias are included in the research first, blunders in collecting and analyzing data such as considering the aggressive behavior of children as an effect of TV shows rather than considering other reasons.

Secondly, accidental communication of the researcher’s opinions to the participants i.e. teachers categorization of bright and dull students makes them believe that they are unable to study and bright students believe that they are extraordinary.

A method as a Source of Extraneous Variability Selection

To avoid the extraneous variables that may cause by the selection of method we must focus on the listed things to avoid such problems


 In an experiment that has different levels of independent variables that receive various treatments to check the effect on dependent variables.

The group must be selected randomly to get the true findings such as randomly assigning the children in two groups rather than intentionally assigning the aggressive one in one group and the non-aggressive in the other group.   

Task and Instructions

 The task is known as those actions that are required to be performed by the participants while measuring the dependent variable.

Let’s take an example of measuring the reaction time i.e., participants press or release the telegraph key as a dependent variable.

Or the material participants will read in an experiment that measures the reading speed of a normal individual.

The difference in comparison must occur due to the experimental conditions rather than extraneous variable such as testing the learning speed you print 10 words 5 in red and 5 in yellow and randomly ask the college students to read it the finding reveal that the red printed words are easy to learn but we must have focused our attention that either the red words are the easier one and yellow words are the difficult one that affects our findings.

Instructions are related to clearly convey the things that the experimenter wants the participants to do in the experiment if they are unclear about something, clear them first and also make sure that they are interested in the experiment after listening to the instructions.

Otherwise, it can directly affect the findings some post-experimentation shows that the difference between results occurs due to the unclear instructions rather than individual differences.

Testing effects

During an experiment, various pre-and post-tests are conducted to know the success rate of an experiment.

It is observed that the differences occur at the beginning of a test and administering it again after the completion of a study.

It may be due to any reason such as after the administration of the first test the participant has an idea about the test and again administer it after some time give them a clue about how he should have to answer which affect our finding as the difference in the pre and post-assessment may be due to the above clues (previous experience of the test) rather than the experiment itself.  

Carryover effects

The carryover effect serves as the extraneous variable when the participant has the previous exposure to the experimental condition that affects the new experimentation.

Such as their previous interaction in an experiment helps them to know the purpose and nature of the study and the participants modify their behavior according to them.

Or sometimes practice related to a specific task provides them mastery in that task which hides their natural ability.


 Instrumentation is also known as an extraneous variable because it includes not only materialistic instrumentation such as electrical and mechanical but also involves participant observation and rate.

Observation after some time is compulsory in research. Changes in the instrumentation also provide changes in the different levels of observation.

Although observers have the skill to notice and categorize specific behaviors but they are humans too they may feel fatigued and become bored due to the task requirements. 

Regression to the Mean

 Regression to mean can also become the cause of extraneous variables such as if a person develops a treatment plan that may help them to lessen the chronic depression in patients.

So first he will administer the scale of chronic depression on a number of people to identify the purposeful sample (those who gain higher scores) after that, he will administer the treatment he designed for them and see its effects on patients based on their improvement.

This can then become the cause of extraneous variables when the results of the study cannot be verified by performing those studies later.

This indicates that while selecting the participants on the base of their score and then post-testing these patients the mean score is more proximal to the population score and causes the regression of mean because the high scorers are taken from the low or high end of a scale.

Whenever you take extreme cases then different factors act together to generate exceptional results.

Although these factors are sometimes temporary and known as chance variables.

Situational variables

although, there is no doubt that the researcher always does his best to control extraneous factors such as day time, a condition so that it cannot affect the findings.

Let’s take an example of an experiment that is conducted in the field would prefer the same time of a day every week but sometimes the extraneous factors such as pollution, loud sounds, light, and weather conditions can disturb the mood and the behavior of the participants in the experiment.

FAQ about Extraneous Variables

Q1. What are the extraneous variables?

Extraneous Variables are those variables that cannot be controlled by the experimenter and also have a serious influence on the result of the experiment.

The foremost four extraneous variables that can disturb the findings are described below

– Demand characteristics (variations in the environment in which the study is conducted)

– Participant Variable (something which is not under the control of the investigator)

– Experimenter Effects (experimenter unintentionally provide some hints related to the participants’ behavior)

– Situational variable  (pollution, loud sounds, light and weather conditions can disturb the mood and the behavior of the participants in the experiment)

2. What is an extraneous variable in research with an example?

There can be a number of variables that can be called as an extraneous variable such as anything that can affect the performance of independent and dependent variable during the research i.e., participants age, height, gender, intellectual level, financial status, culture, traditions, qualification, attitude, behavior and seriousness toward the research

3. How do you control extraneous variables in experimental research?

An extraneous variable can be controlled by different ways such as controlling it from the side of participants considering their maturity age and intellectual level, experimenter considers the experimenter bias and experimenter expectancies and by using the appropriate method of task and instruction, test effect and regression to mean.