Science · Grades 9–12
Investigations, controls and cautious conclusions
Identify the factor changed, the outcome measured and important controlled factors.
Understand the idea
Separate variables
Identify the factor changed, the outcome measured and important controlled factors.
Evaluate uncertainty
Measurement limits, biological variation and sampling can affect results.
Match claim to design
An experiment supports only conclusions justified by its design and data.
Worked examples
In a test of light level and growth, which is the dependent variable if height is recorded?
The dependent variable is the measured outcome.
plant height
Why is random assignment to conditions useful when it is feasible?
It does not guarantee identical groups or remove every source of bias.
It helps distribute pre-existing differences among groups, reducing systematic confounding.
Try it yourself
Repeated readings are very close but all too high because of a miscalibrated instrument. They are
- precise but inaccurate
- automatically valid
- accurate but imprecise
- free of systematic error
Three measurements are 12, 14 and 16 units. Find their mean.
Why should a surprising result be checked rather than immediately deleted?
Which change would confound a test of container colour and cooling rate?
- Using equal liquid volumes
- Changing container material as well as colour
- Measuring at the same intervals
- Using the same thermometer method
Answers and marking notes
Answers and marking notes
- precise but inaccurate
Consistency is precision; closeness to the reference concerns accuracy.
- 14
42/3 = 14.
- It may be a genuine observation or a recording/instrument error. Investigate and document any exclusion rule.
Credit transparency and a reasoned check.
- Changing container material as well as colour
Two explanatory factors change together.
Preview material · independent educational review required. Grade bands are approximate, not official curriculum alignment.