🌡️ Two levels
Typing in a cold room or typing in a warm room. Two versions of the IV are compared.
Experimental Method » Independent and Dependent Variables
What you'll learn this session
Study time: 30 minutes
Cambridge spec: 7.1.3, 7.1.4, 7.1.5
- What the independent variable is, and what its levels (conditions) are
- What the dependent variable is, and four ways to measure it
- How to pick out the IV, its levels and the DV in a new scenario
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Unlock This CourseThe two variables in an experiment
An experiment changes one variable and measures another. Psychologists give these two variables their own names, and you must use them in the exam.
Key terms:
- Independent variable (IV): the variable that is manipulated, which means the one the researcher deliberately changes.
- Levels (conditions): the different versions of the IV. An IV has two or more levels.
- Dependent variable (DV): the variable that is measured.
The independent variable
The IV is the thing the researcher changes. It is called independent because the researcher decides it. It does not depend on anything the participants do.
The IV must have at least two levels, because you need something to compare. Imagine a researcher testing whether room temperature affects typing speed. The IV is the room temperature. It could have two levels: 15°C and 25°C. It could also have three levels: 15°C, 20°C and 25°C. Both are fine, because the syllabus says an IV may have two or more levels.
📊 Three levels
Typing in a cold, a mild or a warm room. More levels give the researcher more to compare.
The levels do not have to be numbers. In a study on how a teaching method affects test scores, the IV is the teaching method, and the levels might be "learning from a video", "learning from a book" and "learning from a teacher".
The dependent variable
The DV is the thing the researcher measures. It is called dependent because its value may depend on the IV. If room temperature really does affect typing, then typing speed depends on temperature.
Psychologists can measure a DV in different ways. The syllabus lists four:
- Experimental tests or tasks: participants do something and get a score. Example: the number of words typed correctly in one minute.
- Observation: the researcher watches and records behaviour. Example: counting how many times a child looks away from a screen.
- Questionnaire: participants answer written questions. Example: rating how tired they feel from 1 to 10.
- Interview: participants answer spoken questions. Example: a researcher asks a participant how stressed they felt and records the answer.
Learn this
The independent variable is the variable that is manipulated. It has two or more levels (conditions). The dependent variable is the variable that is measured. The IV is the cause being tested. The DV is the effect being recorded.
Spotting the IV and DV in a new scenario
In the exam you will read a short scenario you have never seen. Use these two questions:
- What did the researcher change? That is the IV. Name its levels.
- What did the researcher measure? That is the DV. Say how it was measured.
A handy check is to put the two variables into this sentence: "The researcher is investigating the effect of IV on DV." If the sentence makes sense, you have them the right way round.
Practice examples
Try to find the IV, its levels and the DV before you read each answer.
Scenario 1: Colour of paper
A teacher gives 30 students a spelling test on white paper and 30 different students the same test on yellow paper. She counts the spelling mistakes made by each student.
Answer
IV: the colour of the paper. Levels: white and yellow. DV: the number of spelling mistakes, measured by a test.
Scenario 2: Sleep and recall
A researcher asks participants to sleep for 4 hours, 6 hours or 8 hours. The next morning each person learns a list of 20 words and writes down all they can remember.
Answer
IV: the amount of sleep. Levels: 4 hours, 6 hours and 8 hours (three levels). DV: the number of words recalled, measured by a task.
Scenario 3: Watching a film
Children watch either a cartoon with fighting or a cartoon with no fighting. Afterwards, an observer watches them play for 10 minutes and counts how many times each child pushes or hits another child.
Answer
IV: the type of cartoon. Levels: fighting and no fighting. DV: the number of pushes or hits, measured by observation.
Scenario 4: Praise and mood
A researcher praises one group of students after each task and says nothing to another group. At the end, every student completes a questionnaire that asks them to rate their mood from 1 (very low) to 10 (very high).
Answer
IV: whether the students were praised. Levels: praise and no praise. DV: mood rating, measured by questionnaire.
Scenario 5: Seating and talking
Students are seated either in rows or in small circles. After the lesson, a researcher interviews each student and asks how comfortable they felt about speaking in front of others.
Answer
IV: the seating layout. Levels: rows and circles. DV: how comfortable students felt about speaking, measured by interview.
Common mistakes
- Mixing up the IV and DV. Ask "what did the researcher change?" first.
- Writing only "sleep" or "temperature" for the IV and forgetting the levels. If asked for the levels, give each one, such as "15°C and 25°C".
- Naming something the researcher did not change as the IV. The IV is what the researcher manipulates.
- Writing a vague DV such as "memory". Say exactly what was measured, such as "the number of words recalled".
- Giving the IV or DV without using the details of the scenario.
Exam-style question
A researcher investigates whether noise affects how quickly students solve jigsaw puzzles. Twenty students solve a puzzle while a recording of traffic noise is played. Twenty different students solve the same puzzle in a silent room. The researcher records the time, in seconds, that each student takes to finish.
(a) Identify the independent variable in this experiment. [1 mark]
(b) State the levels of the independent variable. [2 marks]
(c) Identify the dependent variable and state how it was measured. [2 marks]
Model answer
(a) The noise level, or whether traffic noise was played (1).
(b) Traffic noise (1) and silence (1).
(c) The time taken to finish the puzzle (1), measured in seconds using a task (1).
Exam tip
Quote the scenario. "Noise level" scores better than "the thing that was changed", and "time taken to finish the puzzle" scores better than "speed".