Extraneous and Confounding Variables in Psychology: Types, Examples, and How to Control Them
In every psychology experiment, researchers aim to test how one variable affects another. But sometimes, unwanted variables can sneak in and influence the results — these are called extraneous variables.
When an extraneous variable actually changes the outcome, it becomes a confounding variable. Understanding and controlling these variables is essential for ensuring valid and reliable results.
Alongside standardisation, randomisation, and counterbalancing, identifying and managing extraneous variables is a key part of good experimental design.
What Are Extraneous Variables in Psychology?
Extraneous variables are any factors other than the independent variable (IV) that could affect the dependent variable (DV).
If these variables are not controlled, they can make it unclear whether changes in the DV were caused by the IV or something else entirely.
🧩 Example:
Imagine you’re testing whether background music affects memory recall.
If some participants are more tired than others, their performance could differ — not because of the music, but because of fatigue.
✅ Fatigue is therefore an extraneous variable.
🧠 What Are the 3 Types of Extraneous Variables?
Psychologists often group extraneous variables into three main types:
1️⃣ Participant Variables
Differences between participants that could influence results — such as age, mood, intelligence, or experience.
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Example: One group may naturally have better memory than another.
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Control: Use a repeated measures design or random assignment to balance groups.
2️⃣ Situational Variables
Features of the environment that may affect the experiment.
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Example: Temperature, lighting, noise, or distractions.
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Control: Apply standardisation to make sure all participants experience the same conditions.
3️⃣ Experimenter (Investigator) Effects
When the researcher’s behaviour unintentionally influences participants.
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Example: Tone of voice, body language, or expectations.
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Control: Use double-blind procedures or automated instructions.
⚠️ What Are Confounding Variables in Psychology?
A confounding variable is an extraneous variable that actually affects the dependent variable — meaning it confounds (mixes up) the cause-and-effect relationship.
🧩 Example:
A psychologist tests whether caffeine improves concentration.
But if participants who drink coffee also slept longer the night before, sleep becomes a confounding variable because it also improves concentration.
This makes it difficult to know whether the results were due to caffeine or sleep.
Difference Between Extraneous and Confounding Variables
| Feature | Extraneous Variable | Confounding Variable |
|---|---|---|
| Definition | Any unwanted variable that might influence the DV | An unwanted variable that actually does influence the DV |
| Effect on Results | Potential threat | Directly changes outcome |
| Example | Participant tiredness | Participant tiredness causing lower recall scores |
| Solution | Control through design | Identify and eliminate after analysis |
How to Control Extraneous Variables
Psychologists use several control techniques to minimise the effects of extraneous variables:
🔹 1. Standardisation
Keep procedures, instructions, and environments identical for all participants.
→ Read: Standardisation in Psychology
🔹 2. Randomisation
Use random allocation to assign participants or order tasks, reducing bias.
→ Read: Randomisation in Psychology
🔹 3. Counterbalancing
Used in repeated measures designs to control order effects like fatigue or practice.
→ Read: Counterbalancing in Psychology
🔹 4. Experimental Controls
Keep the environment, timing, and instructions consistent to eliminate situational factors.
Another major threat to validity comes from demand characteristics — when participants change their behaviour because they think they know the purpose of the study.
Researchers should be aware not only of extraneous or confounding variables, but also of investigator effects in psychology, which can skew results through subtle experimenter influence.
Controlling these variables improves a study’s internal validity — one of the four key types of validity psychologists assess.
Another key control technique is Operationalisation, which helps reduce ambiguity and ensure every variable is clearly measurable.
Extraneous and Confounding Variables in A-Level Psychology (AQA)
In the AQA specification, students are expected to:
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Define and identify extraneous and confounding variables.
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Explain how they threaten validity.
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Describe ways to control them.
Example Exam Question
Explain the difference between an extraneous and a confounding variable. (3 marks)
Model answer:
Extraneous variables are unwanted factors that might influence the dependent variable, while confounding variables are those that actually affect it. Confounding variables make it unclear whether the independent variable or something else caused the results.
FAQs
1️⃣ What is an extraneous variable in psychology?
A factor other than the independent variable that could influence the results of an experiment.
2️⃣ What are the three types of extraneous variables?
Participant variables, situational variables, and experimenter effects.
3️⃣ What is the difference between extraneous and confounding variables?
Extraneous variables might affect results, whereas confounding variables definitely do.
4️⃣ How can you control extraneous variables?
Through randomisation, standardisation, counterbalancing, and consistent experimental procedures.
Reducing extraneous variables helps maintain both internal validity and reliability in psychology, ensuring consistent results across repetitions of a study.
Conclusion
Controlling extraneous and confounding variables is essential for valid, reliable psychological research. Without control, it’s impossible to know whether the independent variable truly caused the observed changes.
By using standardisation, randomisation, and counterbalancing, researchers can design fair and scientifically sound experiments.
While controlling extraneous and confounding variables helps maintain internal validity, researchers must also consider ecological validity — how well their findings apply to real-world settings.
Explore more about how validity shapes high-quality research in our full guide: Types of Validity Psych.
📖 Next read:
- Learn how consistency is tested through different types of reliability in our full guide: Reliability in Psychology.
