Why Do IB Modelling Questions Feel So Under-Specified?
Many IB Mathematics: Applications & Interpretation students feel uneasy when a modelling question seems to leave out key details. The problem may not state exact assumptions, limits, or even the “correct” model to use. This can feel unfair, as if students are being asked to guess what the examiner wants.
IB designs modelling questions to be under-specified on purpose. The aim is to assess decision-making, assumptions, and interpretation, not just calculation. In real-world mathematics, information is rarely complete, and analysts must decide how to proceed responsibly.
What “Under-Specified” Really Means
Under-specified does not mean unsolvable.
It means the question allows:
- Multiple reasonable assumptions
- More than one possible model
- Different valid interpretations
IB expects students to recognise this flexibility and make explicit choices, rather than waiting for perfect instructions that never come.
Why IB Leaves Details Out Intentionally
If IB provided every assumption, modelling would become mechanical.
By leaving gaps, IB can assess whether students:
- Identify relevant variables
- Choose sensible assumptions
- Justify decisions clearly
- Understand limitations of their model
This reflects how mathematics is used in practice, where analysts must decide what matters and what can be simplified.
Why Students Find This So Uncomfortable
Most school maths trains students to look for one correct method.
Under-specified questions break this pattern. Students worry about choosing the “wrong” assumption or model. IB is not looking for perfection — it is looking for reasonableness and justification.
Students often lose marks not because their choice was wrong, but because they failed to explain it.
How Examiners Judge Open Modelling Questions
IB examiners look for:
- Clear statement of assumptions
- Consistency within the model
- Reasonable interpretation of context
- Awareness of limitations
A model does not need to match a single expected answer. It needs to make sense and be explained.
Why This Is Central to Applications & Interpretation
AI Maths focuses on realistic problem-solving.
IB wants students to think like decision-makers, not formula-followers. Under-specified questions force students to engage with uncertainty, which is a core skill in applied mathematics.
Common Student Mistakes
Students frequently:
- Freeze when details are missing
- Assume there is a hidden “correct” model
- Make assumptions but don’t state them
- Avoid interpretation
- Overthink instead of justifying
Most lost marks come from silence, not wrong choices.
How IB Expects You to Handle Missing Information
IB expects students to:
- Make reasonable assumptions
- State those assumptions clearly
- Build a consistent model
- Interpret results cautiously
- Acknowledge limitations
Even simple assumptions, if explained, can earn full marks.
Exam Tips for Under-Specified Questions
Do not wait for perfect information. Choose sensible assumptions and state them clearly. Be consistent throughout your model. Use cautious language like “assumes” or “approximately.” IB rewards clarity and reasoning more than complexity.
Frequently Asked Questions
Can different students get different answers?
Yes. IB allows multiple valid approaches if they are justified and consistent.
Will I be penalised for choosing the “wrong” assumption?
Not if it is reasonable and explained. Lack of explanation is more damaging than choice.
How long should assumptions be?
Usually one or two clear sentences. Brevity with clarity is enough.
RevisionDojo Call to Action
IB modelling questions feel under-specified because judgement is being tested. RevisionDojo helps IB Applications & Interpretation students learn how to make assumptions confidently, justify decisions clearly, and earn marks even in open-ended problems. If modelling questions feel vague or stressful, RevisionDojo is the best place to build control and confidence.
