Extraneous variables

Leverage predictive AI to identify your under-performing creative assets and drive ROAS

Get in touch


Extraneous variables are factors other than the independent variable(s) in an experiment that can influence the outcome or dependent variable(s) being measured. These variables are not of primary interest to the researcher but have the potential to affect the results of the study, leading to erroneous conclusions if not controlled for or accounted for properly.

Here's a detailed breakdown of the concept:

  1. Nature of Extraneous Variables: Extraneous variables can take various forms, including environmental factors, participant characteristics, measurement errors, or uncontrolled experimental conditions. They are often unintended and may arise unexpectedly during the course of the experiment.
  2. Impact on Study Validity: Extraneous variables pose a threat to the internal validity of an experiment by introducing unwanted variability into the data and potentially confounding the relationship between the independent and dependent variables. If left uncontrolled, extraneous variables can obscure the true effects of the independent variable(s) and lead to inaccurate or misleading conclusions.
  3. Controlling Extraneous Variables: Researchers employ several strategies to control extraneous variables and minimize their influence on the outcome of the study. These may include random assignment of participants to experimental conditions, standardizing experimental procedures, using control groups, matching participants based on relevant characteristics, and statistical techniques such as analysis of covariance (ANCOVA).
  4. Random Assignment: Random assignment helps distribute extraneous variables evenly across different experimental conditions by assigning participants to groups in a random manner. This minimizes the likelihood that extraneous variables will systematically bias the results in favor of one condition over another.
  5. Control Groups: Control groups provide a baseline for comparison by allowing researchers to assess the effects of the independent variable(s) in the absence of other influences. By comparing the outcomes of the experimental group(s) to those of the control group, researchers can isolate the effects of the independent variable(s) while controlling for extraneous variables.
  6. Matching: Matching involves selecting participants who are similar on relevant characteristics (e.g., age, gender, socioeconomic status) and distributing them across experimental conditions. This helps ensure that extraneous variables are balanced between groups and do not confound the results.
  7. Statistical Control: Statistical techniques such as analysis of covariance (ANCOVA) can be used to statistically control for the effects of extraneous variables on the outcome variable(s). By including extraneous variables as covariates in the analysis, researchers can adjust for their influence and more accurately assess the effects of the independent variable(s).

In summary, extraneous variables are factors other than the independent variable(s) that can influence the outcome of an experiment. Controlling for extraneous variables is essential for ensuring the internal validity of the study and drawing accurate conclusions about the relationship between variables.


In neuromarketing, controlling for extraneous variables is essential for ensuring the validity and reliability of research findings. Here are the key functions of addressing extraneous variables in neuromarketing:

  1. Isolating Neural Responses: Neuromarketing studies aim to understand how consumers respond to marketing stimuli at a neural level. By controlling for extraneous variables, researchers can isolate the specific effects of marketing interventions on neural activity without interference from unrelated factors. This allows for a clearer interpretation of the neural responses to marketing stimuli.
  2. Enhancing Experimental Validity: Controlling for extraneous variables enhances the internal validity of neuromarketing experiments by reducing the influence of confounding factors on the measured outcomes. This ensures that any observed changes in neural activity can be confidently attributed to the experimental manipulations rather than external influences.
  3. Minimizing Bias: Extraneous variables have the potential to introduce bias into neuromarketing studies, leading to inaccurate or misleading results. By controlling for these variables, researchers can minimize bias and increase the accuracy and reliability of their findings, providing more robust evidence for informing marketing strategies.
  4. Improving Generalizability: Addressing extraneous variables helps ensure that the findings of neuromarketing studies are applicable and generalizable to real-world marketing contexts. By controlling for factors that may vary across individuals or situations, researchers can better understand the underlying neural mechanisms of consumer behavior that apply across diverse populations and market settings.
  5. Enhancing Reproducibility: Reproducibility is a cornerstone of scientific research, including neuromarketing. By controlling for extraneous variables and following rigorous methodological practices, researchers increase the likelihood that their findings can be replicated by other researchers, strengthening the overall reliability and credibility of the field.

Overall, controlling for extraneous variables is essential in neuromarketing to ensure the validity, reliability, and generalizability of research findings. By minimizing the influence of confounding factors, researchers can more accurately uncover the neural mechanisms underlying consumer behavior and provide valuable insights for informing marketing strategies and decision-making.


Let's consider an example of how controlling for extraneous variables is crucial in a neuromarketing study:

Imagine that a company wants to investigate the effectiveness of two different packaging designs for their new energy drink. They collaborate with a neuromarketing research firm to conduct a study using EEG (electroencephalography) to measure participants' brain activity while viewing images of the product packaging.

In the study, participants are divided into two groups: one group sees the energy drink in packaging design A, while the other sees it in packaging design B. The researchers are interested in whether one design elicits stronger neural responses associated with excitement and preference.

However, before conducting the study, the researchers identified several potential extraneous variables that could influence participants' brain activity, such as individual differences in caffeine sensitivity, familiarity with energy drink brands, or mood states.

To control for these extraneous variables, the researchers take several steps:

  1. Participant Screening: They screen participants to ensure they have similar characteristics relevant to the study, such as age, gender, and previous exposure to energy drink advertising. This helps minimize variability due to individual differences.
  2. Random Assignment: Participants are randomly assigned to either packaging design A or B groups to ensure that any differences in brain activity between the groups are not due to pre-existing differences in participant characteristics.
  3. Standardized Procedure: The study follows a standardized procedure, with all participants viewing the product images under the same conditions (e.g., in a quiet room, with consistent lighting) to minimize environmental influences on brain activity.
  4. Control Condition: In addition to the two experimental conditions (packaging design A and B), the researchers include a control condition where participants view neutral images unrelated to the energy drink. This provides a baseline for comparison and helps identify neural responses specific to the product packaging.
  5. Statistical Analysis: After data collection, the researchers use statistical techniques to control for any remaining extraneous variables that may influence the results. For example, they may include covariates in their analysis to adjust for individual differences in caffeine sensitivity or mood states.

By controlling for extraneous variables in their study, the researchers can more confidently attribute any differences in neural responses between the two packaging designs to the design itself, rather than other factors. This enhances the validity and reliability of their findings, providing valuable insights for the company's marketing strategy and product development decisions.

Articles related to 
Extraneous variables
There are two different websites undergoing A/B test and being compared for attention

How to Create and Run an A/B Test on Your Website

If you want to optimize your website, you need to start running A/B tests. Follow these 5 simple steps to ensure you get the most out of your A/B tests!


Subscribe to our monthly newsletter.

Stay ahead of the competition with a monthly summary of our top articles and new scientific research.