A well-planned investigation controls its variables carefully. The independent variable is what you deliberately change. The dependent variable is what you measure as a result. Controlled variables are everything else kept the same, so you can be confident any change in the result is actually caused by the variable you changed, not something else. A reproducible investigation is one detailed and consistent enough that someone else could repeat it and get similar results — this is a cornerstone of trustworthy science. Good planning also means identifying assumptions being made, and, where relevant, recognising and managing any risks or ethical issues (like the wellbeing of any living things involved).
Example
Testing whether sunlight affects plant height: sunlight exposure is the independent variable (deliberately changed), height is the dependent variable (measured), while water, soil type, pot size and plant species are all controlled variables (kept identical) — so any height difference can be confidently attributed to sunlight, not some other factor.
Key terms
Independent variable:
The factor you deliberately change in an investigation.
Dependent variable:
The factor you measure as a result.
Controlled variable:
A factor deliberately kept the same across all groups.
Questions
1. The independent variable is:
What you deliberately change
What you measure as a result
Everything kept the same
Something you never control
2. The dependent variable is:
What you measure as a result
What you deliberately change
A variable that is always ignored
Something with no connection to the investigation
3. Controlled variables are:
Kept the same across all groups
Deliberately changed each time
Never identified in an investigation
Always the same as the independent variable
4. A reproducible investigation is one that:
Someone else could repeat and get similar results
Can never be repeated by anyone else
Has no clear method described
Gives a different result every single time randomly
5. In a sunlight/plant height experiment, height is the:
Dependent variable
Independent variable
A controlled variable
Not a variable at all
6. In a sunlight/plant height experiment, sunlight exposure is the:
Independent variable
Dependent variable
A controlled variable
Not relevant to the experiment
7. Identifying assumptions and managing risks is part of:
Good investigation planning
An unnecessary, irrelevant step
Something only needed after the experiment
A step that has no scientific value
8. Why is it important to keep controlled variables (like water and soil type) the same across all groups in an experiment?
So any difference in the result can be confidently attributed to the variable you actually changed
Controlled variables should always be different for each group
Keeping variables the same makes an experiment less reliable
Controlled variables have no effect on experimental accuracy
9. Why is reproducibility considered a cornerstone of trustworthy science?
If other scientists can repeat a study and get similar results, it strengthens confidence the finding is real, not a fluke
Reproducibility has no bearing on how trustworthy a finding is
A result that can never be repeated is automatically more trustworthy
Reproducible studies are always less reliable than one-off experiments
10. If an experiment testing plant height under different sunlight also used different amounts of water for each group, what problem would this create?
You couldn't be sure whether sunlight or water caused any height difference (an uncontrolled variable)
This would have no effect on the validity of the results
This would make the experiment more scientifically rigorous
Water amount is irrelevant to interpreting the results
11. Why might a scientist explicitly state their assumptions before conducting an investigation?
Being transparent about assumptions helps others evaluate whether the conclusions are justified
Assumptions should always be hidden from other scientists
Stating assumptions has no value in scientific investigation
Investigations never actually rely on any assumptions
12. Why might managing risk be an important part of planning an investigation involving chemicals or living things?
To ensure the safety of researchers, participants, and any living things involved
Risk management has no place in scientific planning
Safety considerations only matter after an investigation is complete
Chemicals and living things never pose any risk in an investigation
13. A "control group" that receives no treatment (e.g. no fertiliser) is used to:
Provide a baseline for comparison against the treated group
Make the experiment less accurate
Replace the need for a hypothesis
Have no useful purpose in the experiment
14. Why might a poorly controlled experiment lead to a false conclusion, even if the data collection itself was accurate?
An uncontrolled variable could be the real cause of the result, rather than the variable being tested
Poor control of variables never affects the validity of a conclusion
Accurate data collection always guarantees a valid conclusion regardless of variable control
Controlling variables is only relevant to the writing stage, not the conclusion
15. Why might detailed, precise documentation of an experiment's method be essential for reproducibility?
Others need enough specific detail to repeat the exact same procedure and fairly compare results
Vague, undocumented methods are just as reproducible as detailed ones
Documentation has no bearing on whether an experiment can be repeated
Reproducibility depends only on the result, never on the method description
16. Why might an investigation with multiple uncontrolled variables be difficult to draw any confident conclusion from at all?
With several factors varying at once, it becomes impossible to isolate which one actually caused an observed effect
Multiple uncontrolled variables always make an experiment more scientifically valid
Uncontrolled variables have no bearing on how confidently conclusions can be drawn
A single result can always be confidently attributed to a specific cause regardless of controls
17. Why might ethical review be especially important for investigations involving animals or human participants, compared to investigations involving only inanimate materials?
Living participants' wellbeing, consent and welfare require careful ethical consideration that inanimate materials do not
Ethical review is equally unnecessary for all types of investigations
Investigations with living participants never require any special ethical consideration
Wellbeing and consent are irrelevant considerations in scientific investigation
18. Why might failing to identify a hidden assumption (e.g. assuming all plants in a sample were the same age) undermine an investigation's conclusions?
An unstated, incorrect assumption could be an unrecognised source of variation affecting the results
Assumptions never actually affect the validity of a scientific conclusion
All assumptions in an investigation are always automatically correct
Hidden assumptions have no bearing on interpreting results accurately
19. Why is planning how variables will be controlled BEFORE starting an investigation more effective than trying to fix it afterward?
Once data collection has started with uncontrolled variables, that data is already compromised and cannot be retroactively fixed
Variables can always be perfectly controlled retroactively after data is collected
Planning variable control in advance has no real benefit over fixing issues afterward
Investigations never need any variable planning at all
20. Two students test the same hypothesis about sunlight and plant height, but one records exact measurement times, equipment and plant variety while the other doesn't. Why is the first student's investigation more valuable to science overall?
Detailed, precise records allow others to check the work and reproduce the investigation reliably
Recording extra detail makes an investigation less scientifically useful
Both investigations are equally valuable regardless of documentation
Reproducibility has no bearing on the value of a scientific investigation
21. Understanding how to plan a fair, reproducible investigation mainly helps you to:
Design experiments that produce reliable, trustworthy and repeatable evidence
Assume any experimental design will produce equally valid results
Ignore the importance of controlling variables
Treat risk and ethical considerations as irrelevant to good science
Answer key (parent copy)
1. What you deliberately change
2. What you measure as a result
3. Kept the same across all groups
4. Someone else could repeat and get similar results
5. Dependent variable
6. Independent variable
7. Good investigation planning
8. So any difference in the result can be confidently attributed to the variable you actually changed
9. If other scientists can repeat a study and get similar results, it strengthens confidence the finding is real, not a fluke
10. You couldn't be sure whether sunlight or water caused any height difference (an uncontrolled variable)
11. Being transparent about assumptions helps others evaluate whether the conclusions are justified
12. To ensure the safety of researchers, participants, and any living things involved
13. Provide a baseline for comparison against the treated group
14. An uncontrolled variable could be the real cause of the result, rather than the variable being tested
15. Others need enough specific detail to repeat the exact same procedure and fairly compare results
16. With several factors varying at once, it becomes impossible to isolate which one actually caused an observed effect
17. Living participants' wellbeing, consent and welfare require careful ethical consideration that inanimate materials do not
18. An unstated, incorrect assumption could be an unrecognised source of variation affecting the results
19. Once data collection has started with uncontrolled variables, that data is already compromised and cannot be retroactively fixed
20. Detailed, precise records allow others to check the work and reproduce the investigation reliably
21. Design experiments that produce reliable, trustworthy and repeatable evidence