Struggling to Spot Extraneous Variables in Psychology? Three Examples That Make It Clear

You can remember the definition of an extraneous variable. But when an exam question gives you a study, suddenly everything looks like a possible answer.

Is it the participants’ age? The room? How much sleep they had? And what are you supposed to write after identifying it?

The trick is to follow a simple chain:

Name the variable → explain how it could affect the measured result → suggest a specific control.

This guide uses three fictional scenarios to help you practise that skill. You will learn to spot problems, explain their consequences and improve the procedure.

What are extraneous variables in Psychology?

An extraneous variable is a variable other than the independent variable that could affect the dependent variable.

In an experiment:

• The independent variable (IV) is what the researcher manipulates.
• The dependent variable (DV) is what the researcher measures.
• Extraneous variables are other factors that could influence that measurement.

Imagine investigating whether background music affects word recall.

The IV is whether music plays during learning. The DV could be the number of words correctly recalled from a list of 20.

However, participants’ existing memory ability, learning time and distractions could also affect their scores.

For a fuller explanation, read our guide to extraneous variables in Psychology.

The updated AQA A-level Psychology research-methods specification includes extraneous variables, operationalisation, control techniques, demand characteristics and investigator effects. These scenarios practise applying those areas. AQA

First, make sure you know what the study measures

You cannot explain how something affects the DV if the DV is unclear.

“Concentration” is too broad on its own. A researcher needs a practical measurement, such as:

The number of target symbols correctly identified on a five-minute visual-search task, with incorrect selections recorded separately.

This is operationalisation: defining a variable in terms of how it will be manipulated or measured.

A precise measure helps you write a precise explanation. Instead of saying “sleep affects the results”, you can explain that tired participants might miss more target symbols.

If this step trips you up, our operationalisation in Psychology guide provides more examples.

Example 1: Did the morning routine really make a difference?

The fictional scenario

A researcher wants to investigate whether two morning-drink routines produce different concentration-task scores in adults.

While exploring possible ingredients, they encounter a commercial article about turkey-tail mushrooms published by https://www.ryzesuperfoods.com/.

The page provides background for the example; its commercial claims are not evidence that a drink improves concentration. The following study and results are entirely invented.

The researcher compares two groups:

Group A identifies more target symbols. The researcher concludes that drink routine A improves concentration.

Pause: what is wrong with that conclusion?

The groups differ in more than their drink routine.

Task duration is an especially clear problem. Group A has twice as long to find symbols. A higher total might reflect extra working time rather than an effect of the drink.

Sleep duration and testing time also provide possible alternative explanations.

A developed answer

Task duration is an extraneous variable because Group A has ten minutes while Group B has five. The additional time could allow Group A to identify more target symbols regardless of the drink routine. Both groups should therefore complete the same task for exactly five minutes.

Notice how the explanation refers to the actual task. “It affects concentration” would be less specific.

How could the procedure be improved?

Both groups should receive the same task duration, instructions and testing conditions. Testing time should also be kept consistent across conditions where practical.

If the aim were to isolate a particular ingredient, the comparison drinks would need to be appropriately matched on other relevant properties. Comparing two different drinks would otherwise test the drinks as a whole, rather than establish which ingredient caused a difference.

A real ingestion study would require appropriate ethical and safety review. This is a written evaluation exercise, not a suggestion to test supplements on classmates.

Example 2: Are flashcards better, or did one group simply revise longer?

The fictional scenario

A teacher compares two revision methods.

• Group A uses flashcards for 20 minutes.
• Group B rereads notes for 10 minutes.
• Both groups then complete a test on the same material.

Group A achieves a higher mean score. The teacher concludes that flashcards are the better method.

Identify the IV and DV

The intended IV is revision method: flashcards or rereading.

The DV is the number of correct answers on the test.

The problem is that revision time also differs between conditions.

A developed answer

Revision duration is an extraneous variable because the flashcard group revises for 20 minutes while the rereading group revises for ten. The extra exposure to the material could increase the flashcard group’s test scores independently of revision method. Both groups should therefore revise for the same duration.

What else should be controlled?

The groups should study equivalent content and receive the same delay between revision and testing.

The teacher should also consider existing differences in knowledge. If the students who already know the topic best all enter the flashcard condition, their higher scores could reflect prior knowledge.

Random allocation can reduce the risk of systematically different groups. It does not guarantee identical groups, particularly with a small sample.

Our guide to randomisation in Psychology explains how chance can be used in research procedures.

A better comparison

A stronger procedure could randomly allocate participants to two conditions, give everyone 15 minutes with equivalent material, and administer the same test after the same delay.

This makes revision method easier to investigate because fewer competing explanations differ systematically between the groups.

Example 3: Does music help, or are different people choosing each condition?

The fictional scenario

A researcher asks participants to choose between completing a proofreading task:

• With instrumental music playing.
• In silence.

The music group identifies more errors. The researcher concludes that music improves proofreading performance.

Spot the problem

Participants chose their own condition.

People who prefer working with music may differ from people who prefer silence. For example, the groups might differ in existing proofreading ability or experience with the task.

Choosing a condition is the allocation problem. Existing proofreading ability is a possible extraneous variable.

Being clear about that distinction makes your answer stronger.

A developed answer

Existing proofreading ability is a possible extraneous variable. Because participants choose their condition, stronger proofreaders might be overrepresented in the music group. Their higher error-detection scores could therefore reflect existing ability rather than the music. Random allocation would reduce the risk of this systematic group difference.

Could repeated measures help?

Yes. Each participant could complete both conditions, allowing them to act as their own comparison.

However, that introduces another problem: order effects.

Participants might improve through practice or perform worse through fatigue on their second task.

Researchers could counterbalance the order:

• Half complete music first, then silence.
• Half complete silence first, then music.

They should use equivalent proofreading passages and balance which passage appears in each condition. Otherwise, remembering the first passage’s errors could affect later performance.

Our experimental-design practice guide provides further help choosing and improving designs.

Why do extraneous variables matter for internal validity?

Internal validity concerns whether the study supports attributing the measured effect to the IV rather than an alternative explanation.

If one revision group has more time, a difference in scores is difficult to attribute specifically to revision method.

Two patterns are useful to recognise:

Do not assume an extraneous variable definitely affected the results. Unless the scenario establishes that, use wording such as “could affect” or “may explain”.

What about demand characteristics and investigator effects?

Not every problem involves time, materials or participant ability.

Demand characteristics are cues that help participants work out the study’s purpose and may change their behaviour.

For example, telling participants “we expect music to improve performance” might encourage them to try harder in the music condition.

Investigator effects occur when researcher behaviour influences participants or the findings.

For example, giving one group extra encouragement could affect their effort.

A standardised procedure, including a consistent instruction script, can reduce unwanted differences in researcher behaviour. Ethical safeguards must still be maintained when deciding what participants are told.

How to turn “it affects the results” into a useful answer

Use this structure:

[Variable] could affect [specific measurement] because [reason connected to the scenario]. The researcher should [specific control], so that [explain what the control achieves].

Compare these answers.

Too vague:

Time is an extraneous variable. It lowers validity. Keep it the same.

Developed:

Learning time is an extraneous variable because one group studies the words for two minutes while the other studies them for one. Longer exposure could increase the number of words recalled independently of the learning method. Both groups should study the same list for exactly one minute.

The second answer shows what the problem is, how it could affect the DV and how to address it.

Your turn: three quick practice questions

These are original practice questions, not official AQA questions or mark schemes.

Question 1

A researcher compares word recall in a quiet room and a noisy room. The quiet group learns 12 common words; the noisy group learns 12 unfamiliar words.

Identify one extraneous variable, explain its possible effect and suggest a control.

Model answer:

Word familiarity is an extraneous variable. Common words might be easier to recall, so the quiet group’s higher score could reflect the words rather than the noise level. Both groups should learn the same word list for the same duration.

Question 2

Participants rate how focused they feel after two different study routines. Before one routine, the researcher says: “This should really improve your focus.”

Explain one problem with this procedure.

Model answer:

The statement creates a demand characteristic by suggesting the expected outcome. Participants might give higher focus ratings because they believe improvement is expected, rather than because they experience greater focus. A neutral, standardised instruction script would reduce this cue.

Question 3

Everyone completes a silence condition first and a music condition second.

Suggest one improvement and explain why it would help.

Model answer:

Counterbalance the condition order so half complete music first and half complete silence first. This spreads practice and fatigue effects across both conditions, reducing the risk that order explains the difference in scores.

A final check before you write your answer

Ask yourself:

1. Have I identified the intended IV and measured DV?
2. What else could influence that specific measurement?
3. Does the scenario actually show that this factor differs?
4. Have I explained its possible effect?
5. Does my control address the problem I identified?

You do not need to list every imaginable flaw. One relevant variable, explained clearly and controlled appropriately, is more useful than several unsupported guesses.

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