Evaluate an investigation and its limitations
Process observations, assess method limitations and reach a proportionate conclusion using qualitative and quantitative evidence.
Section 2.1 · The scientific method
Exam scope and assessment notes
Original StudyForA teaching and practice, not Cambridge-authored questions, mark schemes or official grades. Cambridge expects candidates to study all eight topics, carry out investigative work and learn teacher-selected case studies. This course does not replace a centre's named case-study examples, current local environmental data, supervised fieldwork or the candidate's own investigation. Practice datasets are illustrative, not observations from a real place. No official assessment or certification is provided. The examples and practice datasets in these lessons are fictional and formative; learners must add their centre's verified case studies and current local evidence.
Before you begin
- Cambridge recommends prior environmental/science study equivalent to IGCSE or O Level. This is an AS-only qualification; use the exam-year syllabus and confirm centre entry details.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What makes environmental evidence useful?
What you will learn
- Record a transparent investigation method and data trail
- Identify limitations and propose practical improvements
- Draw a conclusion that matches the evidence and sampling scope
Keep the method reproducible
Record the aim, location, sample design, instruments, units, timing, safety and raw observations. Present data with a suitable table, graph or map and retain the calculation steps.
Do not delete unusual data only because it changes a mean. Investigate whether it is an error, a valid extreme or unresolved; document any exclusion rule.
Link each limitation to its consequence
A limitation is useful when it explains what the method may miss and how this affects the conclusion. Small sample size, biased locations, one time point and uncertain instruments have different consequences.
Suggest improvements that address the limitation and remain practical. The final claim should not extend beyond the place, period and variables actually studied.
Sources for this lesson
Pause and explain
How should an improvement address a stated limitation?
Worked example
A heat survey measures five street temperatures at noon on one day. Identify two limitations and an improved design.
Show the worked solution
- Consider spatial and temporal representativeness.
- Check shade, surface and instrument consistency.
- Repeat at sites and times using a recorded protocol.
Answer Five noon readings on one day may miss differences between streets and times. Shade, surface and recent weather also affect readings. Repeat across a stratified range of sites and times using the same calibrated instrument and record local conditions.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A litter survey finds higher counts near a bus stop than in a park. Write a cautious conclusion and one limitation.
Give me a hint
Report the pattern and restrict the conclusion to the sampled sites.
Compare my reasoning
- Identify the relevant data, place or process in the prompt.
- Apply record a transparent investigation method and data trail to the stated context.
- Explain the inference and one limitation or trade-off.
The sampled bus-stop locations had higher litter counts than the sampled park locations. The survey cannot show bus use caused the difference; footfall, bin access and collection timing may matter. If there was only one site per type, the result may not represent other locations.
Look for these in your work
- Record a transparent investigation method and data trail
- Uses relevant evidence and explains the environmental mechanism
- Distinguishes observation, inference and limitation
A student removes the highest turbidity reading as an outlier because it changes the mean. What should happen instead?
Give me a hint
Check the observation and keep a transparent record.
Compare my reasoning
- Identify the relevant data, place or process in the prompt.
- Apply identify limitations and propose practical improvements to the stated context.
- Explain the inference and one limitation or trade-off.
Check instrument operation and field notes. The value may reflect error or a real pollution event. Repeat the sample if possible, keep the original value and justify any exclusion using a stated rule rather than its effect on the mean.
Look for these in your work
- Identify limitations and propose practical improvements
- Uses relevant evidence and explains the environmental mechanism
- Distinguishes observation, inference and limitation
A conclusion says planting 'solved flooding' after one small storm. Rewrite it proportionately.
Give me a hint
Describe the event and sample, then name further monitoring.
Compare my reasoning
- Identify the relevant data, place or process in the prompt.
- Apply draw a conclusion that matches the evidence and sampling scope to the stated context.
- Explain the inference and one limitation or trade-off.
During the observed small storm, sampled points showed less surface runoff. This suggests planting may reduce runoff under those conditions, but larger storms and longer monitoring are needed before judging flood risk overall.
Look for these in your work
- Draw a conclusion that matches the evidence and sampling scope
- Uses relevant evidence and explains the environmental mechanism
- Distinguishes observation, inference and limitation
Common mistakes
- Naming a limitation without its likely effect
- Removing an outlier without a documented reason
- Making a conclusion broader than the sample
What can you explain now?
How should an improvement address a stated limitation?
Compare with the explanation
It changes the method in a way that reduces the limitation's effect
An improvement should be practical and clearly connected to the weakness.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
What are the three parts of a useful method limitation?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.