A good economics explanation has three parts: the cause, the mechanism and the effect. The mechanism is the step most students leave out, and it is the step the marks usually reward.
This lesson is part of economic reasoning and evaluation. If you also need to show your reasoning with a sketch, continue to using diagrams to support an answer.
What are the three parts?
Use this frame: “Because [cause], [mechanism], so [effect on price and quantity].”
| Part | Question it answers | Example wording |
|---|---|---|
| Cause | What changed? | A flood destroyed part of the harvest |
| Mechanism | Why does that change the market? | Sellers can offer fewer bundles at each price |
| Effect | What happens to price and quantity? | Price rises, quantity traded falls |
Each part is one sentence. If a part is missing, the answer reads like a label instead of an explanation.
Worked example: the kangkung flood
In the fictional Kampung Paya, kangkung sells at RM2 a bundle and 500 bundles are traded each day. A flood ruins part of the crop.
Weak answer: “The price of kangkung rises because of the flood.”
This names a cause and an effect, but nothing links them. A reader cannot tell whether you understand why.
Strong answer: “The flood damaged the crop, so farmers can offer fewer bundles at every price. Supply shifts left. At RM2, buyers still want 500 bundles but sellers offer fewer, so there is a shortage. Competition among buyers pushes the price up to RM3, and quantity traded falls to 350 bundles.”
The strong answer has four steps in order: cause, shift, shortage, new price and quantity. Every sentence adds something the last one did not.
Which mistakes cost marks?
- Skipping the middle. Writing “flood, so price rises” with no supply shift.
- Wrong curve. Saying demand fell when the flood affected sellers.
- Half an effect. Stating the price change and forgetting quantity.
- Repeating. Writing “supply falls, so less is supplied” as if it were a second step.
Before you write, ask: which curve did the cause move? That one question fixes most wrong-curve errors.
Check yourself
Household incomes in a fictional town rise, and a branded sandal is a normal good. Explain the effect on the sandal market using cause, mechanism and effect.
Answer
Because incomes rose, buyers can afford more sandals at every price, so demand shifts right. At the old price, quantity demanded is now greater than quantity supplied, which creates a shortage. Sellers raise the price, and this encourages them to offer more, so the market settles at a higher price and a larger quantity.
The cause is the income rise, the mechanism is the rightward demand shift and the shortage, and the effect is a higher price and higher quantity.
What to study next
Practise the frame on a full set in the economic reasoning and evaluation practice. The claim and evidence revision desk helps you rewrite a weak answer into a strong one.
To have a teacher go through your written chains with you, see online one-to-one Economics tuition.