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What are extraneous variables: Examples, types and controls (2024)

If you are conducting research or experiments, it is essential to understand the concept of extraneous variables and how to manage them.

February 8, 2024
Team Blitzllama

In research and product development, extraneous variables lurk as silent disruptors. They stealthily interfere with our findings and blur the clarity of our insights. For product owners and UX researchers, recognizing these variables is paramount. 

They can range from subtle environmental cues to participant characteristics, skewing results and distorting interpretations. Understanding the types — such as situational, individual, and environmental — empowers researchers to mitigate their influence effectively. 

Our article discusses extraneous variables, provides real-world examples, and proposes actionable strategies for controlling them. By mastering these principles, product owners and UX researchers can ensure the integrity and reliability of their work.

What is an extraneous variable?

An extraneous variable is a factor outside the scope of a study that can influence its outcomes. It's a variable not intentionally studied but can affect the results. For instance, in user experience research, screen brightness or device speed might be extraneous variables. 

They're not the focus but can impact how users interact with a product. Identifying and controlling extraneous variables is crucial for accurate findings. Through careful design and methodology, researchers can minimize their effects. 

Product owners need to consider these variables to ensure their products meet user needs effectively. Understanding extraneous variables enhances the validity and reliability of research outcomes.

Now that we've established the significance of extraneous variables, let's delve into why considering them is so important for product owners and UX researchers.

Why does considering extraneous variables matter?

Product owners and UX researchers must grasp the impact of extraneous variables on research outcomes. Failing to account for these variables can lead to skewed results, making it difficult to draw valid conclusions. 

Why does considering extraneous variables matter?

Consideration of extraneous variables enhances the robustness of research, enabling more accurate insights into user experience and product performance:

1) Confusing Correlation with Causation

Imagine testing a new feature that boosts user engagement. Suddenly, sales spike! Is the feature the hero, or is something else at play? Extraneous variables like a seasonal trend or a competitor's blunder can create a false correlation, making you think the feature caused the sales increase when it didn't. This can lead to wasted resources pushing the "wrong" solution.

2) Hidden Biases

Remember that perfect user who fits your ideal persona? They might not exist. Participant selection bias creeps in when you recruit users who don't represent your target audience. This skews your data, making it irrelevant to your actual users. Similarly, confirmation bias can lead you to focus on data that confirms your pre-existing beliefs, ignoring valuable insights that challenge them.

3) Context Matters

Imagine testing a new checkout process on a desktop website and replicating it for mobile. But what if mobile users are more likely to be on the go, with shorter attention spans? This context difference can invalidate your findings, leading to a clunky mobile experience that frustrates users.

Now that we understand the significance of considering extraneous variables, let's delve into the different types that researchers encounter.

Types of extraneous variables

Extraneous variables can be classified into several types from participant variables to demand characteristics. Each type of extraneous variable presents unique challenges and considerations for researchers to address in their studies:

Types of extraneous variables

1) Participant variables

Participant variables encompass characteristics inherent to individuals involved in a study. These factors may influence their responses and behaviors, thereby affecting the reliability and validity of research findings. Demographics such as age, gender, and cultural background can significantly impact how participants engage with tasks or stimuli. For instance, older adults might approach tasks differently than younger individuals due to generational disparities in technology usage or cognitive abilities.

Personality traits also play a crucial role in shaping participant responses. Traits like introversion or extroversion can affect how individuals interact with experimental tasks or environments. Moreover, prior experiences, including education, professional background, or exposure to similar studies, may influence participants' perceptions and behaviors during research sessions.

Motivation levels vary among participants and can impact their engagement and effort in completing tasks or providing accurate responses. Participants with higher motivation levels may exhibit greater perseverance and attention to detail, while those with lower motivation may demonstrate decreased performance or interest in the study's objectives.

2) Situational variables

Situational variables encompass external factors within the research environment that may influence participant behavior and responses. Environmental conditions such as noise level, lighting, and temperature can impact participants' comfort and concentration levels during research sessions. High levels of noise or poor lighting conditions may introduce distractions and hinder participants' ability to focus on tasks or stimuli.

The time of day at which research sessions occur can also influence participant responses. Circadian rhythms and daily fluctuations in energy levels may affect participants' alertness and cognitive performance. For instance, research conducted during early morning hours may yield different results compared to sessions conducted in the afternoon or evening due to variations in participants' mental acuity and responsiveness.

Testing conditions, including the layout of the research space and availability of resources, can impact participants' experiences and behaviors. Factors such as seating arrangements, room temperature, and access to technological devices may affect participants' comfort levels and their ability to engage with study materials effectively.

3) Experimenter effects

Experimenter effects refer to unintentional biases or behaviors exhibited by researchers that may inadvertently influence participants' responses and behaviors during research sessions. These effects can manifest through verbal cues, body language, or subtle nonverbal signals conveyed by experimenters.

Researchers' expectations and beliefs about study outcomes may inadvertently influence how they interact with participants and administer experimental procedures. Subtle verbal cues or facial expressions may unintentionally communicate expectations or influence participants' interpretations of tasks and instructions.

Furthermore, experimenter characteristics such as gender, age, or perceived authority can impact participants' perceptions and compliance with research protocols. Participants may be more inclined to conform to expectations or provide socially desirable responses in the presence of authority figures or individuals perceived as experts in the field.

4) Demand characteristics

Demand characteristics refer to cues or contextual information within the research setting that suggest expected behaviors or responses from participants. These cues may inadvertently influence participants' interpretations of study objectives and shape their responses accordingly.

The wording of questions and instructions provided to participants can inadvertently convey researchers' expectations or hypotheses, leading participants to adjust their responses to align with perceived study objectives. Ambiguities or leading language in instructions may inadvertently bias participants' interpretations of tasks or stimuli.

Moreover, the design of experimental materials and stimuli may contain subtle cues or contextual information that guide participants' responses or perceptions. Visual cues, formatting choices, or the presentation of stimuli may inadvertently signal expected responses or influence participants' decision-making processes.

Understanding the types of extraneous variables helps researchers recognize potential sources of interference in their research designs. Next, let's explore examples of extraneous variables specifically in the context of UX research.

Examples of extraneous variables in UX research

In UX research, extraneous variables can manifest in various forms, such as participant characteristics, task conditions, and environmental factors. These variables have the potential to influence user behavior and perceptions, thereby impacting the outcomes of usability studies and user testing sessions:

Case Study 1: Usability testing of a mobile app with participants from different age groups.

When testing a mobile app across various age demographics, age-related factors can significantly impact user interactions and feedback.

How age might impact interaction with the app's interface:

  • Younger users may be more adept at navigating complex interfaces and may prefer minimalist designs with sleek animations.
  • Older users might encounter difficulties with small fonts or intricate gestures, preferring simpler layouts with larger elements.

How prior experience with similar apps might influence feedback:

  • Users accustomed to other apps may compare the tested app with their previous experiences, affecting their perception of usability and features.
  • Seasoned users might provide nuanced feedback, whereas novices may struggle to articulate specific issues.

Case Study 2: A/B testing of two website designs with different color schemes.

During A/B testing of website designs, several external factors can influence participants' perceptions and preferences.

How the testing environment's lighting might affect perceived color differences:

  • Dim lighting conditions can obscure subtle color variations, potentially skewing participants' perceptions of contrast and aesthetics.
  • Bright lighting may amplify color disparities, making distinctions between design elements more pronounced.

How the order in which users see the designs might influence their preference:

  • Participants exposed to one design before the other may exhibit primacy or recency effects, favoring the first or last design encountered.
  • Sequential exposure can introduce biases, as participants may compare subsequent designs against their initial impressions.

Case Study 3: In-depth interviews with users about their experiences with a new product.

During in-depth interviews, researchers must account for various factors that could influence participants' responses and insights.

How the interviewer's body language might influence participant responses:

  • Nonverbal cues such as facial expressions or gestures can inadvertently shape participants' answers, leading to responses that align with the interviewer's perceived expectations.
  • Subtle cues of agreement or disapproval may prompt participants to modify their responses to align with the interviewer's stance.

How social desirability bias might lead to inaccurate feedback:

  • Participants may provide socially desirable responses to project a favorable self-image or conform to perceived societal norms.
  • Fear of judgment or embarrassment can deter participants from expressing genuine opinions or negative experiences, leading to skewed feedback.

Now that we've identified common examples of extraneous variables in UX research, it's essential to discuss strategies for controlling these variables to ensure the integrity of study results.

How to control extraneous variables

Controlling extraneous variables involves implementing strategies to minimize their impact on the study outcomes. This may include standardizing experimental procedures, randomizing participant assignments, and conducting pilot tests to identify potential sources of variability:

How to control extraneous variables

1) Standardization

Standardization involves maintaining consistency in the testing environment, instructions, and procedures to minimize the influence of extraneous variables. For digital products, this means ensuring that all users interact with the software under the same conditions. For instance, if testing a mobile app, make sure participants use the same device model, operating system version, and network connection speed. Consistency in instructions and procedures helps in obtaining reliable data across different user sessions.

2) Randomization

Randomization involves randomly assigning participants to different groups to control for potential biases and confounding variables. In digital product testing, randomization ensures that each user has an equal chance of being assigned to a specific experimental condition or group. For example, in a usability study comparing two versions of a website, randomly assigning participants to each version helps in minimizing the impact of individual differences on the results, leading to more robust findings.

3) Blinding

Blinding, particularly double-blind tests, helps in reducing experimenter and participant bias by concealing information that could influence the outcome. In digital product research, double-blind tests involve keeping both the participants and the researchers unaware of certain conditions or variables being tested. For example, in a study evaluating the effectiveness of a new messaging feature in a social media app, neither the participants nor the researchers know who is using the new feature and who is not, to prevent biased responses.

4) Pilot testing

Pilot testing involves conducting a small-scale trial run of the study to identify and address potential extraneous variables before conducting the main study. In the context of digital products, pilot testing allows researchers to uncover usability issues, technical glitches, or unforeseen user behaviors that could affect the validity of the results. For instance, before launching a large-scale usability study of a new e-commerce platform, conducting a pilot test with a small group of users helps in refining the research protocol and ensuring a smooth data collection process.

5) Matching participants

Matching participants involves pairing individuals or groups based on key characteristics to control for potential confounding variables. In digital product research, matching participants ensures that the groups being compared are similar in relevant traits such as age, gender, experience level, or technological proficiency. For example, when comparing the user experience of a mobile banking app across different age groups, matching participants based on age helps in isolating the impact of age-related factors on user perceptions and behaviors.

6) Regression analysis

Regression analysis allows researchers to examine the relationship between multiple variables and determine their combined influence on the outcome of interest. In digital product research, regression analysis helps in identifying the relative importance of various factors affecting user behavior or performance. For instance, in a study analyzing factors influencing app retention rates, regression analysis can reveal the extent to which factors like user demographics, app features, and usability metrics contribute to user retention, enabling product owners to prioritize interventions accordingly.

By implementing effective control measures, researchers can enhance the internal validity of their studies and draw more accurate conclusions from their findings. Next, we'll discuss best practices for product owners and UX researchers to mitigate the influence of extraneous variables in their work.

Best practices for product owners & UX researchers

Product owners and UX researchers can collaborate to mitigate the influence of extraneous variables by establishing clear research objectives, selecting appropriate research methodologies, and systematically addressing potential sources of bias throughout the research process. 

By prioritizing rigorous study design and execution, product teams can gather meaningful insights to inform product development decisions and enhance the user experience:

Planning and Designing Studies:

1) Proactively Identify Potential Extraneous Variables:

In the initial stages of planning, product owners and UX researchers should anticipate potential factors that may influence study outcomes. For instance, when testing a new mobile app feature, consider variables like device types, operating systems, and network conditions that could impact user experience. Identifying these variables early on helps in developing a comprehensive research plan.

2) Choose Appropriate Control Strategies Based on Research Goals and Resources:

Selecting effective control strategies is crucial in isolating the impact of the variable of interest. For instance, if evaluating the usability of a website's interface, control for browser variations and screen resolutions. Tailoring control strategies to align with research goals and available resources ensures a focused and efficient study.

3) Pilot Test and Refine Procedures to Minimize Extraneous Effects:

Before launching a full-scale study, conduct pilot tests to identify and address potential issues. For example, when testing a new e-commerce checkout process, pilot tests can uncover navigation challenges or payment gateway issues. Refining procedures based on pilot findings helps optimize the study design, minimizing the influence of extraneous variables.

Communicating Findings:

1) Acknowledge the Presence and Potential Impact of Extraneous Variables:

Transparent communication is essential in research reporting. Acknowledge the presence of extraneous variables and their potential impact on the study. For instance, when analyzing user feedback on a social media platform redesign, mention the influence of users' familiarity with previous layouts as a potential extraneous variable.

2) Discuss Limitations and How They Were Addressed:

Clearly articulate the limitations encountered during the research process and detail the steps taken to mitigate them. For instance, if testing a new software's performance on different devices, discuss the challenge of obtaining a diverse set of devices for testing and how it was addressed, such as through simulated environments or collaboration with beta testers.

3) Focus on Actionable Insights Despite These Limitations:

Despite inherent limitations, emphasize the practical and actionable insights gained from the study. For instance, if studying user engagement with a new productivity app faced limitations due to time constraints, highlight key takeaways like the most preferred features or common pain points. This approach ensures that despite constraints, valuable insights are communicated to guide product improvements.


In summary, identifying and managing extraneous variables is pivotal for product owners and UX researchers. These variables, whether lurking in the background or subtly influencing outcomes, can jeopardize the reliability of research findings. Vigilant awareness of potential confounding factors is crucial, as they can distort the true impact of interventions or design changes. Employing robust controls, such as randomization and counterbalancing, enhances the validity of studies by minimizing the interference of extraneous variables. Upholding a meticulous approach to research design ensures that conclusions drawn are grounded in the genuine effects of interventions, enabling informed decision-making for product development and user experience enhancements.