Uncontrolled experiments (AQA GCSE Statistics): Revision Notes
📚Revision Notes
Uncontrolled experiments
When conducting research, scientists sometimes need to study real-world situations where they cannot control all the factors that might influence their results. This is where uncontrolled experiments become valuable tools for gathering data in more realistic settings.
What are uncontrolled experiments?
Uncontrolled experiments are research studies conducted in everyday, natural environments where the researcher cannot control all the variables that might affect the outcome. Unlike controlled laboratory experiments, these studies take place in real-world settings, making them more representative of actual behaviour and circumstances.
Note
In uncontrolled experiments, researchers still identify explanatory variables (the factors they believe cause changes) and response variables (the outcomes they measure). However, they must also be aware of extraneous variables - other factors that could influence the results but cannot be controlled or eliminated.
Types of uncontrolled experiments
There are two main types of uncontrolled experiments, each with different levels of researcher involvement:
Field experiments
Field experiments take place in natural, everyday environments, but the researcher still has some degree of control over the experimental setup. The researcher can arrange the situation and manage certain variables, even though the overall environment remains uncontrolled.
Example
Field Experiment Example: Arthritis Treatment Study
A researcher investigating a new treatment for arthritis might assess patients' mobility before introducing the treatment, then measure their mobility again after the treatment period.
- Explanatory variable: The new treatment being tested
- Response variable: The change in patient mobility levels
- Advantages: Results are more likely to reflect genuine real-life behaviour since participants are in natural settings
- Disadvantages: Cannot control extraneous variables such as how active patients are at home or other factors that might influence mobility
Natural experiments
Natural experiments occur in completely uncontrolled environments where the researcher has no control over any variables. Instead, they observe and measure what happens naturally without any intervention.
Example
Natural Experiment Example: Speed Limit Changes
Studying how a reduction in speed limits affects car accident rates by comparing accident numbers before and after the speed limit change.
- Explanatory variable: The change in speed limit
- Response variable: Number of accidents recorded
- Advantages: Highly realistic since behaviour occurs naturally without researcher interference
- Disadvantages: Cannot control any variables, making it difficult to replicate the study or eliminate alternative explanations
Working through examples
Let's examine a practical example to understand how uncontrolled experiments work:
Example
Worked Example: Breakfast and Student Performance Study
Scenario: Claire wants to investigate whether eating breakfast helps student performance. On Day 1, she asks students to attend college without breakfast before taking a maths test. On Day 2, she asks the same students to eat breakfast before coming to college for another similar maths test.
Analysis: This represents a field experiment because Claire has arranged the conditions (breakfast vs no breakfast) but cannot control the natural college environment or other factors that might affect performance.
Advantages: The study reflects real student behaviour in their actual learning environment.
Disadvantages: Many extraneous variables could affect the results, such as:
- Amount of sleep students had each night
- Students' natural learning from the first test
- Different difficulty levels between the two tests
- Students' motivation levels on different days
Key considerations for exam success
Important
When analysing uncontrolled experiments, always consider:
- Type identification: Can the researcher control any variables (field) or none at all (natural)?
- Variable identification: What is being changed (explanatory) and what is being measured (response)?
- Extraneous variables: What other factors could influence the results?
- Advantages vs disadvantages: Weigh realistic settings against lack of control
Summary
Key Points to Remember:
- Uncontrolled experiments occur in real-world settings where not all variables can be controlled
- Field experiments allow some researcher control over setup and conditions
- Natural experiments involve no researcher control - just observation of naturally occurring events
- Main advantage: Results are more realistic and applicable to real life
- Main disadvantage: Difficulty controlling extraneous variables makes it harder to establish clear cause-and-effect relationships