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examBoard: AQA
examType: GCSE
lessonTitle: Experimental Method Introduction
Experiments are one of the most important research methods in psychology. They allow researchers to test cause and effect relationships between variables in a controlled way. This makes them a powerful tool for testing psychological theories and hypotheses.
Key Definitions:
Experiments are the only research method that allows psychologists to establish cause and effect. This is because researchers can manipulate variables directly and control other factors that might influence the results. If you want to know whether something causes something else, an experiment is usually the best choice.
Experiments follow the scientific method, which involves making observations, forming hypotheses, testing these hypotheses through controlled experiments and drawing conclusions. This systematic approach helps ensure that findings are reliable and valid.
There are three main types of experiments used in psychological research. Each has its own advantages and disadvantages.
Conducted in controlled settings like a psychology lab. Researchers have high control over variables, but the artificial setting might affect how people behave.
Example: Milgram's obedience study where participants were asked to deliver electric shocks to another person in a lab setting.
Conducted in real-world settings but still involve manipulation of variables. More natural behaviour but less control over extraneous variables.
Example: Piliavin's subway study on helping behaviour, conducted on actual subway trains.
Take advantage of naturally occurring events or situations. Researchers don't manipulate variables but observe the effects of natural changes.
Example: Studying the psychological effects on children who experienced a natural disaster compared to those who didn't.
Understanding variables is crucial for designing good experiments. There are several types of variables that psychologists need to consider.
The variable that the researcher manipulates or changes. It's the potential cause in a cause-effect relationship.
Example: In a study on the effect of sleep on test performance, the amount of sleep would be the independent variable.
The variable that is measured to see if it changes as a result of manipulating the independent variable. It's the potential effect.
Example: In the same sleep study, test scores would be the dependent variable.
Any variables other than the IV that might affect the DV. These need to be controlled to ensure the experiment is valid.
Examples: Age, gender, time of day, room temperature, noise levels, etc.
Extraneous variables that are kept constant across all conditions of the experiment.
Example: Using the same room, same time of day and same instructions for all participants.
The way an experiment is designed affects its validity and the conclusions that can be drawn. There are three main experimental designs:
Different participants are used in each condition of the experiment.
Advantages: No order effects, simple to design
Disadvantages: Individual differences between groups can affect results
The same participants take part in all conditions of the experiment.
Advantages: Controls for individual differences
Disadvantages: Order effects can occur (e.g., practice, fatigue)
Participants are matched on key characteristics and then split into different conditions.
Advantages: Controls for individual differences without order effects
Disadvantages: Difficult to match participants perfectly
To ensure that changes in the DV are due to the IV (and not something else), psychologists use various techniques to control extraneous variables:
This famous experiment investigated how language can affect memory. Participants watched videos of car accidents and were asked 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] each other?"
Independent Variable: The verb used in the question (smashed, hit, contacted)
Dependent Variable: Participants' estimates of the cars' speed
Design: Independent groups (different participants in each verb condition)
Findings: Participants who heard "smashed" estimated higher speeds (41 mph) than those who heard "contacted" (32 mph), showing how language can influence memory.
When designing an experiment, follow these steps:
When answering questions about experimental methods:
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