Database results:
    examBoard: AQA
    examType: GCSE
    lessonTitle: Controlling Extraneous Variables
Psychology - Cognition and Behaviour - Research Methods - Research Procedures - Controlling Extraneous Variables - BrainyLemons
« Back to Menu 🧠 Test Your Knowledge!

Research Procedures » Controlling Extraneous Variables

What you'll learn this session

Study time: 30 minutes

  • What extraneous variables are and why they matter in psychological research
  • Different types of extraneous variables you need to know
  • Methods for controlling extraneous variables
  • How to evaluate control techniques in research studies
  • Real-world examples of controlling variables in psychological experiments

Understanding Extraneous Variables

When psychologists conduct research, they need to make sure their results are valid and reliable. One of the biggest challenges is dealing with unwanted factors that might mess up their findings. These unwanted factors are called extraneous variables.

Key Definitions:

  • Extraneous variables: Any variable, other than the independent variable, that might affect the dependent variable in an experiment.
  • Confounding variables: Extraneous variables that have actually influenced the results, making it impossible to know whether changes in the dependent variable were caused by the independent variable or something else.

💡 Why Control Matters

Imagine you're testing whether a new revision technique helps students remember more information. If one group is tested in a noisy room and another in a quiet room, the noise level (an extraneous variable) might affect your results more than the revision technique itself!

⚠ The Problem

Without proper control of extraneous variables, we can't be sure if our results are due to our independent variable or something else entirely. This threatens the validity of our research and makes our findings less useful.

Types of Extraneous Variables

Extraneous variables can come from many sources. Here are the main types you need to know for your GCSE:

👤 Participant Variables

Differences between participants like age, gender, intelligence, personality, mood, or motivation that might affect how they respond.

🔬 Situational Variables

Aspects of the environment where the research takes place, such as noise, lighting, temperature, time of day, or presence of others.

📝 Researcher Variables

How researchers might influence participants through their behaviour, expectations, or instructions (also called experimenter effects).

Methods for Controlling Extraneous Variables

Psychologists use several techniques to control unwanted variables. The method chosen depends on the research design and practical considerations.

1. Standardisation

This involves keeping procedures exactly the same for all participants. It's one of the most common control methods.

✅ What to Standardise

  • Instructions given to participants
  • Testing environment (room, lighting, temperature)
  • Time of day for testing
  • Equipment used
  • Researcher behaviour and appearance

📖 Example

In a memory test, all participants would receive identical instructions, be tested in the same room, with the same researcher, at similar times of day and have the same amount of time to complete the task.

2. Random Allocation

This involves randomly assigning participants to different conditions or groups in an experiment.

🎲 How It Works

By using methods like drawing names from a hat, using random number generators, or flipping a coin, researchers ensure that participant characteristics (like age, gender, or intelligence) are evenly distributed across conditions.

💪 Strengths

Random allocation helps control for individual differences between participants. It means any differences between groups are likely due to chance rather than systematic bias.

Case Study Focus: Loftus and Palmer (1974)

In their famous eyewitness testimony experiment, Loftus and Palmer controlled extraneous variables by:

  • Using standardised procedures - all participants watched the same car crash videos
  • Using the same questionnaire format for all participants
  • Randomly allocating participants to different question conditions
  • Testing all participants in similar environments

This helped ensure that the only systematic difference between groups was the critical word used in the question about car speed ("smashed", "collided", "bumped", etc.).

3. Counterbalancing

This technique is used when participants take part in more than one condition of an experiment, to control for order effects.

🔀 Order Effects

When participants do multiple tasks, their performance might be affected by:

  • Practice effects: Getting better at later tasks due to practice
  • Fatigue effects: Getting tired and performing worse on later tasks
  • Boredom effects: Losing interest in later tasks

📝 Example

If testing two memory techniques (A and B):

  • Half the participants do technique A first, then B
  • The other half do technique B first, then A

This way, any order effects should balance out across the whole sample.

4. Matching

This involves creating groups that are similar in terms of important participant variables.

🤝 How It Works

Researchers identify key characteristics (like age, gender, or IQ) and ensure these are balanced across experimental groups. For example, if one group has five 15-year-old boys, the other group should have a similar number.

💭 When It's Useful

Matching is particularly useful when:

  • Sample sizes are small
  • Certain participant characteristics are likely to strongly influence results
  • Random allocation might not create balanced groups

5. Single-Blind and Double-Blind Techniques

These techniques help control for bias and expectancy effects.

👁 Single-Blind

Participants don't know which condition they're in (e.g., whether they're receiving a real treatment or a placebo). This helps control for participant expectancy effects, where people's expectations influence how they respond.

👀 Double-Blind

Neither the participants nor the researchers directly interacting with them know which condition participants are in. This additionally controls for experimenter bias, where researchers might unconsciously treat participants differently based on their expectations.

Evaluating Control Methods

✅ Strengths

  • Increases internal validity of research
  • Makes it more likely that changes in the DV are due to the IV
  • Allows for more confident conclusions about cause and effect
  • Makes research more replicable

❌ Limitations

  • Can make research settings artificial and reduce ecological validity
  • Some variables are impossible to control completely
  • Strict controls can be time-consuming and expensive
  • May limit the types of research questions that can be investigated

Exam Tip: Evaluating Research

When evaluating psychological studies in your exam, always consider:

  • What extraneous variables might have affected the results?
  • What methods did the researchers use to control these variables?
  • Were these control methods effective?
  • Could any confounding variables have influenced the findings?

Being able to identify potential problems with variable control is a key skill that will help you achieve higher marks!

Applying Your Knowledge

Understanding how to control extraneous variables isn't just important for your exams it's a crucial skill for evaluating research claims in everyday life. When you hear about a new psychological finding in the news, ask yourself: "Did the researchers properly control for other explanations?" This critical thinking approach will serve you well beyond your GCSE Psychology course!

🧠 Test Your Knowledge!
Chat to Psychology tutor