Every economic model simplifies. To evaluate one, state who is not in it (people or groups) and what is not in it (costs, time, quality, other effects), then say how much that could change the conclusion. This is a common route to higher-level marks in written answers.
The lesson closes specialisation and allocation, and the skill returns in nearly every later module, including economics data responses.
How do I find what a model leaves out?
Ask five questions:
- Who is missing? Buyers, sellers, workers, neighbours, the government, future generations.
- What costs or benefits are missing? Transport, waiting time, quality, effects on third parties.
- What is assumed constant? Prices elsewhere, skills, tastes, weather.
- What time span does it cover? A single week may hide longer changes.
- How big could the omission be? A small omission may not change the result.
Worked example
Take the Bukit Padi bakers from the productivity gain lesson. The model says that Sara baking only loaves and Imran making only kuih raises output from 54 to 64 items. State what it leaves out.
Who is missing. Customers: the model does not say whether anyone wants 40 loaves and 24 trays. Other bakers who might compete are also absent.
What is missing. The model ignores the time to trade the two products and any transport cost. It also assumes both bakers produce at the same quality and speed all day, and that Imran is willing to bake kuih only.
Assumptions. Output rates are fixed and each person can fully switch tasks.
Judgement. If customers wanted equal numbers of each product, 40 loaves and 24 trays would not be what the market wants. The gain in total output is real in the model, but the benefit to consumers depends on demand, which the model does not include.
What mistake do students make?
The usual slip is a vague line such as “the model is not realistic”.
Mistaken answer: The model is too simple and not realistic.
It says nothing specific, so it earns little credit.
Correct it by naming one person or factor, saying why it matters here, and saying how the result might change. “It ignores customers, so extra loaves may go unsold and the real gain could be smaller.”
Check yourself
1. In the Orchard Hill durian schedule, name one group not included in the model.
Show answer
Buyers: the schedule shows what the farm supplies, not what customers will buy at each price. Other farms are also not shown.
2. The Selatan Bay example assumes the catch stays the same when the tuna price falls. Give one way this assumption might not hold.
Show answer
Fishing firms might reduce their catch if the lower price makes fishing less profitable, so income could fall by more than the model shows.
3. Write one evaluative sentence about the Kampung Seri flour table.
Show answer
“The table leaves out the quality of flour and the cost of queuing, so a maximum price could change buyers’ experience in ways the quantity figures do not show.”
Where does this lead next?
Return to the module overview for the full route, then try the mixed practice set to use all five lessons together. Notes on weak spots can go into the mistake log.
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