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examBoard: AQA
examType: GCSE
lessonTitle: Extraneous Variables
When psychologists conduct research, they need to be sure that any changes they observe are actually caused by what they're testing (the independent variable) and not by something else. These unwanted "something else" factors are called extraneous variables and they can seriously mess up research results if not properly controlled.
Key Definitions:
Imagine you're testing whether a new revision technique helps students improve their test scores. If some students in your study also hired private tutors (an extraneous variable), you wouldn't know if improvements were due to your technique or the tutoring!
Psychologists aim to establish cause and effect relationships between variables. Extraneous variables threaten this by offering alternative explanations for results. Controlling them helps ensure research validity.
Extraneous variables can sneak into psychological research in many ways. Here are the main types you need to know:
These relate to individual differences between participants that might affect results:
These relate to the environment where the research takes place:
These relate to how the researcher might influence the study:
Extraneous variables can impact research in two main ways:
Internal validity refers to how confident we can be that changes in the dependent variable were actually caused by the independent variable. Extraneous variables threaten this by offering alternative explanations for the results.
When extraneous variables aren't controlled, they can become confounding variables that are so mixed up with the independent variable that we can't tell which one caused the changes we observed.
One famous example of an extraneous variable comes from studies conducted at the Hawthorne Works factory in the 1920s and 1930s. Researchers were investigating how workplace conditions affected productivity. They found that productivity improved when changes were made to lighting levels.
However, they later discovered that productivity improved regardless of whether lighting was increased or decreased! This led to the identification of what we now call the Hawthorne Effect - the tendency for people to change their behaviour simply because they know they're being observed. This awareness of being studied was an extraneous variable that affected the results.
Psychologists use several methods to control extraneous variables and ensure their research is valid:
Randomly allocating participants to different conditions helps ensure that participant variables are evenly distributed across conditions.
Example: In a study testing a new therapy, researchers would randomly assign participants to either receive the therapy or be in a control group.
Using the same procedures, instructions and conditions for all participants helps control situational variables.
Example: Giving all participants exactly the same instructions, read from a script, in the same room, at the same time of day.
Pairing participants with similar characteristics across different conditions.
Example: Ensuring each condition has the same number of males and females, or participants of similar ages or educational backgrounds.
Participants don't know which condition they're in (experimental or control), reducing demand characteristics.
Example: Participants don't know whether they're receiving a real treatment or a placebo.
Neither participants nor researchers know which condition participants are in, reducing both demand characteristics and experimenter bias.
Example: In drug trials, neither participants nor the researchers directly interacting with them know who's receiving the actual drug versus a placebo.
Changing the order of conditions or tasks to prevent order effects.
Example: Half the participants do Task A then Task B, while the other half do Task B then Task A.
When reading about psychological studies or designing your own research, it's important to be able to spot potential extraneous variables. Here are some questions to ask:
In their famous study on eyewitness testimony, Loftus and Palmer showed participants videos of car accidents and then asked them questions about what they saw. The key manipulation was the verb used in the question: "How fast were the cars going when they smashed/hit/contacted/bumped/collided into each other?"
The researchers needed to control several extraneous variables, including:
If they hadn't controlled these variables, they couldn't have been confident that differences in speed estimates were due to the verb used (independent variable) rather than these other factors.
Understanding extraneous variables is crucial for:
When you're asked to evaluate studies in your exams, identifying potential extraneous variables and discussing how well they were controlled is a key way to demonstrate critical thinking.
If you need to design a study for coursework, showing awareness of potential extraneous variables and how you'll control them will strengthen your methodology.
In your psychology exams, you might be asked to:
When answering these questions:
To avoid confusion, remember the differences between variable types:
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