Experiments: variables and operational definitions
Identify independent and dependent variables, define them so they can be measured, and apply experimental reasoning to new situations.
Original teaching mapped to Cambridge IGCSE Psychology 0266 Version 3 for 2027–2029. The course is independent study support, not Cambridge material, an official mark scheme or an awarded grade. Named-study notes summarise the required findings; candidates are not expected to evaluate named studies. Self-check practice is not official grading, a timed Paper 1/2 simulator or teacher review.
Before you begin
- Use the Version 3 syllabus and confirm availability in your administrative zone with Cambridge and your school. Both papers are compulsory. The updated named-study summaries are required context; full original research articles are not required.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Before experiments: variables and operational definitions, which approach is most useful?
What you will learn
- Describe an experiment as a controlled test of one variable’s effect on another
- Identify IV conditions and the measured DV
- Operationalise a manipulation and a behavioural measure
- Apply these terms to novel scenarios
An experiment tests a change under controlled conditions
An experiment investigates the effect of one variable on another while relevant conditions are controlled. The independent variable (IV) is manipulated and may have two or more conditions. The dependent variable (DV) is measured; a test, task, observation, questionnaire or interview can provide that measure.
Operationalisation makes a variable observable
To operationalise a variable, define exactly what changes or what will be counted, timed or rated. ‘Concentration’ is broad; ‘number of correctly identified symbols in two minutes’ is measurable. Clear definitions help the study test its aim and make the procedure repeatable.
Keep the question and measurement aligned
If a study asks whether background music affects recall, music condition is the IV and a clearly defined recall score is the DV. A useful answer names each variable, states its levels or measurement, then explains how those choices fit the question.
Pause and explain
Which response best shows understanding of experiments: variables and operational definitions?
Worked example
A researcher tests whether a quiet or noisy room affects the number of words remembered after one minute. Identify and operationalise both variables.
Show the worked solution
- The researcher changes the room sound condition.
- The participant’s recall is measured as a score.
- State the precise levels and scoring rule.
Answer IV: quiet versus noisy room. DV: number of list words correctly recalled after one minute.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A study varies the delay before a memory test and counts correct answers. Name and operationalise the IV and DV.
Give me a hint
One is changed, the other is counted.
Compare my reasoning
- The delay is changed by the researcher.
- The number of correct answers is counted.
- These are the IV and DV respectively.
IV: delay before testing, stated in minutes/conditions. DV: number of correct answers.
Look for these in your work
- Identifies manipulation
- Identifies measured score
- Uses clear operational terms
Why is ‘helpfulness’ a weak DV description for an observation study? Improve it.
Give me a hint
Define a behaviour an observer could consistently record.
Compare my reasoning
- ‘Helpfulness’ can mean different things to different observers.
- Choose an observable action, such as offering to pick up a dropped item.
- State how it will be counted during a fixed period.
Operationalise it as the number of times a participant offers assistance during a defined 10-minute observation.
Look for these in your work
- Explains vagueness
- Chooses observable behaviour
- Adds a measurement rule
A researcher asks whether short breaks improve proofreading. Propose a suitable IV and DV without inventing results.
Give me a hint
Specify the break conditions and measurable proofreading outcome.
Compare my reasoning
- Set the IV as no break versus a five-minute break.
- Measure proofreading with a defined score, such as errors correctly spotted on the same-length passage.
- Keep the task and scoring rule consistent across conditions.
IV: break condition. DV: number of errors correctly spotted on a fixed proofreading task.
Look for these in your work
- Operationalises IV
- Operationalises DV
- Includes a control for comparability
Common mistakes
- Calling the measured outcome the IV.
- Using a vague DV such as ‘memory quality’.
- Assuming an experiment requires a laboratory; experiment types are not required here.
What can you explain now?
Which variable is measured in an experiment?
Compare with the explanation
Dependent variable
The researcher manipulates the IV and measures the DV.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
How do IV, DV and operationalisation make an experiment testable?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.