Experimental Method » What Is an Experiment?
What you'll learn this session
Study time: 30 minutes
Cambridge spec: 7.1.1, 7.1.2
- What an experiment is in psychology
- The three features: one variable changed, another measured, conditions controlled
- Why experiments can show cause and effect
- How to decide whether a new scenario is an experiment, and explain why
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Unlock This CourseWhere this fits in the exam
This lesson starts the Research Methods theme. The experimental method is examined in Paper 1, Section D (30 marks), which covers sections 7.1 and 7.5 to 7.9 of the syllabus.
What is an experiment?
Psychologists want to know why people think and behave as they do. Does noise make it harder to learn? Does a good night's sleep improve memory? An experiment is the method used to test questions like these.
Key terms:
- Experiment: a method of investigating the effect of one variable on another variable, under controlled conditions.
- Variable: anything that can change or take different values, such as the amount of sleep, the number of words remembered or a person's age.
- Controlled conditions: the researcher keeps everything else the same, so that nothing else can affect the results.
The three features of an experiment
Every experiment has three parts. Learn them as a simple rule: change one thing, measure another, keep everything else the same.
🔄 Change one thing
The researcher deliberately changes one variable. They decide what happens, rather than just watching.
📏 Measure another
The researcher measures a second variable to see whether it is affected by the change.
🔒 Keep the rest the same
Everything else is controlled. The same task, the same instructions, the same room and the same time allowed.
The next lesson gives the exact names for the two variables. For now, you only need to be able to spot them in a description.
Why control matters
Imagine a researcher wants to know if listening to music changes how many maths questions students answer correctly. Half the students work in silence. The other half work with music on. The researcher counts the correct answers.
Now imagine the silent group did a hard test and the music group did an easy test. If the music group scored higher, you could not tell whether the music or the easier test caused it. Because the researcher did not keep everything else the same, the result is useless.
When the conditions are controlled, the only thing that differs is the one variable the researcher changed. So if the scores differ, the change is the most likely reason. This is why experiments can be used to judge cause and effect: whether one thing makes another thing happen.
Learn this
An experiment is a method of investigating the effect of one variable on another variable, under controlled conditions. The researcher changes one variable, measures another and keeps everything else the same, so cause and effect can be judged.
Applying the idea to new scenarios
In the exam you will be given a short description of a study you have never seen. You may be asked to decide whether it is an experiment and to give a reason. Use this checklist:
- Did the researcher change something? Look for a variable that they set or manipulated.
- Did they measure something else? Look for a score, time, count or rating.
- Did they keep other things the same? Look for matching tasks, instructions or timings.
If all three are present, it is an experiment. If the researcher only watched, or only asked questions, it is not.
Scenario 1: Revision and recall
A teacher asks one group of students to study a list of 20 words for two minutes by repeating them out loud. A second group studies the same list for two minutes by making up a story with the words. Both groups are tested on how many words they recall after ten minutes. Is this an experiment? Explain your answer. [2 marks]
Model answer
Yes, it is an experiment (1). The researcher changed how the words were studied, measured the number of words recalled and kept the list, the time and the test the same (1).
Scenario 2: Playground watching
A researcher sits quietly at the edge of a playground for an hour and writes down how many times children share their toys. Is this an experiment? Explain your answer. [2 marks]
Model answer
No, it is not an experiment (1). The researcher only watched and did not change any variable or control any conditions (1).
Scenario 3: Breakfast survey
A researcher gives 50 students a written list of questions about how often they eat breakfast and how well they think they concentrate in lessons. Is this an experiment? Explain your answer. [2 marks]
Model answer
No (1). The researcher only asked questions and did not change one variable and measure its effect under controlled conditions (1).
Experiments in the syllabus
You will meet named studies later, for example Craik and Tulving in the lesson Craik and Tulving Study Analysis, which changed the kind of question asked about each word and measured how many words were remembered. Here you only need to know what makes a study an experiment. The syllabus does not ask you to know different types of experiment.
Common mistakes
- Calling any study an experiment. Watching behaviour or giving out questions is not an experiment, because nothing is changed.
- Forgetting to say that the conditions are controlled. Without it, you cannot judge cause and effect.
- Giving a reason without using the scenario. Always mention what was changed and what was measured, using the details in the question.
- Writing that an experiment proves something. Say that it investigates the effect of one variable on another.
Exam-style question
A researcher wants to find out whether drinking water before a test affects how well students concentrate. One group of 20 students drinks a glass of water before a 10-minute puzzle. Another group of 20 students drinks nothing before the same puzzle. Both groups do the puzzle in the same room, with the same instructions, at the same time of day. The researcher counts how many puzzle pieces each student fits together.
(a) State what is meant by an experiment. [2 marks]
(b) Explain why this study is an experiment. [3 marks]
(c) Explain why it is important that both groups used the same room and instructions. [2 marks]
Model answer
(a) A method of investigating the effect of one variable on another variable (1), under controlled conditions (1).
(b) The researcher changed whether the students drank water (1). They measured the number of puzzle pieces fitted together (1). They kept other things the same, such as the room, the instructions and the time of day (1).
(c) So that nothing else could affect the number of pieces fitted (1). This means any difference between the groups is more likely to be caused by the water, so cause and effect can be judged (1).
Exam tip
For "explain why this is an experiment", write one point for each feature: what was changed, what was measured and what was kept the same. Quote the details from the scenario.