Let's analyze each scenario in the table to identify the
independent variable (the factor that is manipulated or changed by the experimenter) and the
dependent variable (the outcome that is measured or observed).
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Scenario 1:
> A cow is given a growth hormone and then compared to another cow that was not given a growth hormone. Both cows were weighed at 2 years.
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Independent Variable: Whether the cow received a growth hormone (Yes/No)
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Dependent Variable: Weight of the cow at 2 years
✔ Explanation: The researcher manipulates whether the cow gets the hormone, and measures the resulting weight.
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Scenario 2:
> Mosquito repellent is sprayed on one arm and the other arm is not sprayed. The number of mosquito bites is counted after 2 hours.
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Independent Variable: Application of mosquito repellent (sprayed vs. not sprayed)
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Dependent Variable: Number of mosquito bites
✔ Explanation: The treatment (repellent or no repellent) is controlled; the result (number of bites) is measured.
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Scenario 3:
> One group is placed in tap water and another group is placed in salt water. The change in their mass is measured after 1 day.
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Independent Variable: Type of water (tap water vs. salt water)
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Dependent Variable: Change in mass
✔ Explanation: The type of water is manipulated; the change in mass is the outcome being measured.
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Scenario 4:
> Two different cars are traveling at 60 mph. At a certain point, both cars turn on their brakes. Researchers record how much time it takes for each car to stop.
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Independent Variable: Type of car (different models)
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Dependent Variable: Time it takes to stop
✔ Explanation: Although speed is constant, the car model is varied (manipulated), and stopping time is measured.
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Scenario 5:
> Pillbugs are placed in a container where they have a choice of a wet or a dry environment. Researchers record how much time was spent in each side.
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Independent Variable: Environment (wet vs. dry)
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Dependent Variable: Amount of time spent in each side
✔ Explanation: The environment is manipulated (offered as a choice), and behavior (time spent) is recorded.
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Scenario 6:
> A stapler is used to staple 100 papers. It jams 5 times during the trial. A different brand of stapler performs the same task. It jams 22 times.
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Independent Variable: Brand of stapler
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Dependent Variable: Number of jams
✔ Explanation: The brand (type of stapler) is changed; the number of jams is the outcome measured.
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Scenario 7:
> Cockroaches are exposed to a pesticide. After 3 hours, 95% of the insects are dead.
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Independent Variable: Exposure to pesticide (yes/no)
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Dependent Variable: Percentage of cockroaches dead
✔ Explanation: The presence of pesticide is manipulated; death rate is the observed result.
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✔ Final Answer Table:
| Scenario | Independent Variable | Dependent Variable |
|--------|----------------------|--------------------|
| 1 | Growth hormone (given or not) | Weight of the cow |
| 2 | Mosquito repellent applied or not | Number of mosquito bites |
| 3 | Type of water (tap vs. salt) | Change in mass |
| 4 | Type of car | Time to stop |
| 5 | Environment (wet vs. dry) | Time spent in each side |
| 6 | Brand of stapler | Number of jams |
| 7 | Exposure to pesticide | Percentage of insects dead |
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This analysis helps students understand how to distinguish between variables in experimental design — the independent variable is what you
change, and the dependent variable is what you
measure.
Parent Tip: Review the logic above to help your child master the concept of independent variable vs dependent variable worksheet.
