An outward shift of a production possibility curve means the economy can now produce more of one or both goods. It shows greater potential output, but it does not show who benefits, and it does not mean every group is better off.
This lesson finishes scarcity, choice and opportunity cost. It builds on movements along the curve, where resources are only shifted between goods.
What causes the curve to shift?
- More resources: a larger labour force or newly found natural resources.
- Better quality resources: training and education for workers.
- Better technology: machines or methods that raise output per worker.
A movement along the curve is different. It is a choice between goods using the same resources. A shift is a change in what the resources can do.
How to interpret a shift, step by step
- Name the cause and link it to a factor of production.
- State the change in potential output, using the numbers.
- Say whether actual output rises, which depends on using the resources.
- Ask who gains and who does not, and give at least one group for each.
- Write a balanced conclusion that avoids “everyone”.
Worked example
Tanjung Island, from the previous lesson, can make at most 60 tonnes of rice or 50 boats.
A new irrigation system is built in the valley. The maximum rice rises from 60 to 75 tonnes. The maximum boats stay at 50, because the system does not help boat building.
So the curve shifts outward on the rice axis only. At 20 boats, the island could make 48 tonnes before. After the shift, assuming rice capacity rises in the same proportion at every point (75 ÷ 60 = 1.25 times), it could make 48 × 1.25 = 60 tonnes, so potential rice rises by 12 tonnes without giving up any boats.
Now the question: “Everyone on the island is better off. Do you agree?” Here is what happens to the 600 households.
| Group | Households | Monthly income before (RM) | After (RM) |
|---|---|---|---|
| Valley farmers using irrigation | 200 | 1,000 | 1,400 |
| Fishing households | 300 | 1,000 | 1,000 |
| Hill rice labourers, replaced by pumps | 100 | 800 | 700 |
Average income before: (200 × 1,000 + 300 × 1,000 + 100 × 800) ÷ 600 = 580,000 ÷ 600 = about RM967.
Average income after: (200 × 1,400 + 300 × 1,000 + 100 × 700) ÷ 600 = 650,000 ÷ 600 = about RM1,083.
The average rises by about RM117, around 12%. Yet the hill labourers’ income falls by RM100, and fishing households see no change.
A balanced answer: “The shift raises Tanjung’s potential output and average income. However, the gains go mainly to valley farmers, while hill labourers lose income, so it is not true that all groups benefit. Whether the island is better off overall depends on how the gains are shared, which a PPC cannot show.”
The mistake to watch for
Mistaken answer: “The curve moved outward, so everyone is better off.”
The student read a diagram of the whole economy as if it showed every household.
A PPC shows total potential output, not its distribution. The correction is to add the qualifier: potential output rises, so there is scope for gains, but who gains is a separate question that needs evidence.
A second slip is saying the shift must raise actual output. It only does so if the extra capacity is put to use.
Check yourself
1. Which would shift Tanjung’s curve outward: (a) a fall in the price of rice, (b) a training programme that raises worker skills, (c) people choosing to buy more boats?
Show answer
Only (b). Training improves the quality of labour. (a) and (c) change what people choose, not what the economy can make.
2. After the shift, Tanjung still produces 20 boats and 40 tonnes of rice. Has actual output increased?
Show answer
No. Potential output rose, but the island is making the same as before. Resources are still unused.
3. Write one sentence evaluating the claim “average income rose, so everyone gains”.
Show answer
For example: “Average income rose from about RM967 to about RM1,083, but hill labourers earned RM100 less, so not every group gained.”
Where this leads next
Test the whole topic with the scarcity, choice and opportunity cost practice set, then move to specialisation and allocation. The ratios with interpretation limits tool shows how an average can hide differences.
Evaluation sentences are where many Economics marks are won or lost. Our teachers practise them in online one-to-one Economics tuition, keeping every example neutral.