Defining the variables in an experiment
Label the three roles in any test: the one you change, the one you measure, and the ones you keep the same.
- Telling cause from effect: Naming the variable you change vs. the one you measure depends on first telling a cause from its effect.
- Choosing something measurable: A dependent variable has to be something you can actually measure, so picking a measurable outcome comes first.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
The independent variable is the one factor you change, the dependent variable is the outcome you measure, and the controlled variables are everything you keep the same so they can't affect the result.
A team has subjects get 4, 6, or 8 hours of sleep, then records each subject's reaction time on a ruler-drop test the next morning. Everyone is the same age range, tested at the same time of day, with the same test. Which is the dependent variable?
Reviewed- A.The hours of sleep assigned
- B.The reaction time recorded on the ruler-drop test
- C.The time of day of the test
- D.The age range of the subjects
Show the worked solution ▾
Answer: B. The reaction time recorded on the ruler-drop test
- Step 1: Find what's changed on purpose: The hours of sleep are changed on purpose, so that's the independent variable: not the answer here.
- Step 2: Find what's measured: Reaction time is the outcome they record to see the effect, so it is the dependent variable.
Why it's right: Reaction time is the outcome the team measures to see the effect of the sleep, which is the definition of the dependent variable.
- A: The hours of sleep are the independent variable: the factor they change, not measure.
- C: Time of day is held the same for everyone, so it's a controlled variable.
- D: Age range is kept the same across subjects, so it's a controlled variable.
Aligned to Biomedical Innovation: independent vs. dependent variable · reading level ~grade 9
- A lab notebook has three labeled lines: change, measure, keep the same: that students fill in before running any experiment.
Fill these in as you work through the lesson.
- Independent variable (the one factor you change on purpose):
- Dependent variable (the outcome you measure):
- Controlled variable (a factor kept the same so it can't affect the result):
- Variable (any factor in the experiment that could change):
You change the variable, you measure the variable, and you hold the variables the same.
- In a test of how hours of sleep affect reaction time, which variable do you change and which do you measure?
- Why must everything except the independent variable be held the same?
- Name two controlled variables for a study on how hours of sleep affect reaction time.
Experiment: a team has subjects get a set amount of sleep (4, 6, or 8 hours) and then records each subject's reaction time on a ruler-drop test. Same age range, same time of day, same test. Label the independent variable, the dependent variable, and two controlled variables.