Planning and conducting a fair investigation

A fair test changes only one variable at a time (the independent variable) while keeping everything else the same (controlled variables), so you can be confident that any change in the result (the dependent variable) was actually caused by the variable you changed. Careful investigations also consider risks and safety, and choose equipment that can measure precisely and reliably. A reproducible investigation is one that's planned and recorded clearly enough that someone else could repeat it and get similar results.

Key terms

Independent variable:

The one thing you deliberately change in an experiment.

Dependent variable:

The thing you measure, which may change because of the independent variable.

Controlled variable:

Something kept the same across all groups so it doesn't affect the result.

Questions

1. 1. In a fair test, you should change:

   • Everything at once
   • Only one variable at a time
   • Nothing at all
   • A different variable each trial randomly

2. 2. The independent variable is:

   • The thing you measure
   • The one thing you deliberately change
   • Something kept the same
   • Irrelevant to the experiment

3. 3. The dependent variable is:

   • The thing you measure as a result
   • The thing you change
   • Always the same
   • Irrelevant

4. 4. A controlled variable is:

   • Something you change
   • Something kept the same across all groups
   • The final result
   • Never important

5. 5. A reproducible investigation is one that:

   • Can never be repeated
   • Is planned clearly enough for someone else to repeat it
   • Gives different instructions each time
   • Has no clear method

6. 6. Safety should be considered:

   • Never
   • When planning an investigation
   • Only after something goes wrong
   • Only by teachers

7. 7. Precise equipment helps you:

   • Get less accurate results
   • Measure more accurately and reliably
   • Skip measurements entirely
   • Guess results

8. 8. In an experiment testing fertiliser's effect on plant height, the independent variable is:

   • Plant height
   • The amount of fertiliser
   • The pot colour
   • The room temperature

9. 9. In the same experiment, the dependent variable is:

   • The amount of fertiliser
   • Plant height
   • The pot size
   • The plant species

10. 10. Which of these should be a controlled variable in the fertiliser experiment?

    • Amount of fertiliser
    • Plant height
    • Amount of water given to each plant
    • Nothing needs to be controlled

11. 11. If you accidentally give different amounts of water to different plant groups while testing fertiliser, this:

    • Improves the experiment
    • Introduces an uncontrolled variable that could affect the results unfairly
    • Has no effect on fairness
    • Is required for a fair test

12. 12. Why is it important that an investigation be reproducible?

    • So no one else can check it
    • So other scientists can verify the results by repeating it
    • Reproducibility is unimportant
    • So results can be kept secret

13. 13. Choosing appropriate, precise equipment mainly helps you:

    • Get less reliable data
    • Collect more accurate and trustworthy data
    • Skip the experiment
    • Avoid all measurement

14. 14. Considering risks before an experiment mainly helps:

    • Increase danger
    • Keep everyone safe during the investigation
    • Make the experiment less scientific
    • Slow down results for no reason

15. 15. An experiment testing whether temperature affects reaction rate accidentally uses different chemical concentrations across trials. This mistake:

    • Has no effect on the experiment's validity
    • Introduces a second uncontrolled variable, making it hard to know what caused any change
    • Improves the fairness of the test
    • Is required for good science

16. 16. Why is testing only one variable at a time important for drawing valid conclusions?

    • It ensures any observed change can be confidently linked to that one variable, rather than several possible causes
    • It makes the experiment take longer for no reason
    • Multiple variables should always be changed together
    • It has no real benefit

17. 17. A student's experiment cannot be repeated by others because the method wasn't recorded clearly. This investigation lacks:

    • Independent variables
    • Reproducibility
    • Any variables at all
    • A hypothesis

18. 18. Which represents the best controlled experimental design testing the effect of light on seed germination?

    • Vary light, water and temperature all together across groups
    • Vary only light exposure, keeping water, temperature, soil and seed type the same across groups
    • Use different seed types for each light level
    • Change the light level randomly with no record

19. 19. Why might a scientist use precise, calibrated equipment instead of rough estimation when collecting data?

    • Rough estimation is always more accurate
    • Precise equipment reduces measurement error and increases confidence in the results
    • Precision has no bearing on data quality
    • Calibration is unnecessary for real experiments

20. 20. Understanding fair testing and controlled variables is essential in science mainly because it:

    • Allows for confident, valid conclusions about cause and effect
    • Makes experiments more confusing
    • Has no real purpose
    • Removes the need for a hypothesis