Production possibility curves

Economics· Unit 1: Basic Economic Ideas and Resource Allocation· 15 min read

1. What is a Production Possibility Curve?★☆☆☆☆⏱ 5 min

The PPC (sometimes called the production possibility frontier, PPF) is a simple two-good model that illustrates the core basic economic problem of scarcity. It assumes fixed quantities of available factors of production (land, labour, capital, enterprise) and constant technology in the economy.

📘 Definition

Production Possibility Curve

A graphical representation of the maximum combinations of two goods that can be produced with an economy's current factors of production and technology.

Example:

An economy producing only capital goods and consumer goods

📐 Worked Example

Draw a PPC for an economy producing wheat and cars, and label points that are productively efficient, inefficient, and unattainable.

1
Label the vertical axis 'Quantity of wheat' and horizontal axis 'Quantity of cars'.
2
Plot all maximum output combinations, then connect them to form a downward-sloping curve concave to the origin.
3
Label any point on the PPC: this is productively efficient, meaning all resources are fully employed.
4
Label any point inside the PPC: this is inefficient, as there are unused or underemployed resources.
5
Label any point outside the PPC: this is unattainable with the economy's current resources and technology.

2. Opportunity Cost and the Slope of the PPC★★☆☆☆⏱ 5 min

The downward slope of the PPC directly illustrates opportunity cost: to produce more of one good, an economy must give up production of the other. A concave (bowed out from origin) PPC reflects increasing opportunity cost, meaning as you produce more of one good, the opportunity cost (in terms of the other good) rises. A straight line PPC reflects constant opportunity cost.

📐 Worked Example

An economy has a straight line PPC with maximum wheat output of 100 million tonnes and maximum car output of 20 million units. Calculate the opportunity cost of producing 1 car.

1
For a straight line PPC, the total opportunity cost of producing the maximum quantity of cars is all the wheat that could have been produced instead.
2
Opportunity cost per car = Total wheat given up / Total cars produced =
3
$\frac{100 \text{ million tonnes}}{20 \text{ million cars}} = 5 \text{ tonnes of wheat per car}$
4
The opportunity cost of 1 car is 5 tonnes of wheat.

✓ Quick check

Test your understanding:

What is the opportunity cost of 1 tonne of wheat in the example above?
- 0.2 cars
- 5 cars
- 20 cars
- 100 cars
Reveal answer
0.2 cars —
Correct: $\frac{20 million cars}{100 million tonnes} = 0.2$ cars per tonne of wheat.

3. Movements Along vs Shifts of the PPC★★☆☆☆⏱ 6 min

CIE examiners frequently test the difference between movements along an existing PPC and shifts of the entire PPC. Movements along the PPC occur when an economy reallocates existing resources between producing the two goods, leaving total productive capacity unchanged. Shifts of the entire PPC occur when the economy's total productive capacity changes, from changes in the quantity or quality of factors of production or technology.

📐 Worked Example

Identify whether each event causes a movement along the PPC or a shift of the PPC: (1) An economy increases production of capital goods by reducing production of consumer goods. (2) An improvement in technology increases output of both goods.

1
For (1): Reallocating existing resources does not change the economy's maximum productive capacity, so this is a movement along the existing PPC.
2
For (2): Improved technology increases maximum possible output of both goods, so this causes an outward shift of the entire PPC.

4. Shifts of the PPC and Economic Growth★★★☆☆⏱ 4 min

Outward shifts of the PPC represent long-run economic growth, as the economy can now produce more of both goods. The direction of the shift matters for exam questions: if technology or productivity improves only for one good, the shift will be skewed towards that good, not a uniform outward shift.

📐 Worked Example

A country discovers large new oil reserves. Show the effect of this discovery on its PPC between consumer goods and capital goods.

1
New oil reserves increase the total quantity of natural resources available to the country, which increases maximum productive capacity for both types of goods.
2
Draw a new PPC parallel and outward from the original PPC, with both maximum consumer good output and maximum capital good output higher than before.
3
This outward shift represents economic growth for the country.

5. Common Pitfalls

Wrong move:

Mixing up the meaning of points inside and outside the PPC

Why:

Many candidates swap the definitions, confusing attainability and efficiency

Correct move:

Remember: points inside the PPC are attainable but inefficient, points outside are unattainable with current resources

Wrong move:

Claiming a reallocation of resources shifts the entire PPC

Why:

Shifts require a change in total productive capacity, not just a change in how resources are used

Correct move:

Reallocation of existing resources only causes a movement along the existing PPC

Wrong move:

Drawing a straight line PPC for all scenarios

Why:

Most real-world economies have increasing opportunity cost, so the PPC is concave

Correct move:

Draw a concave (bowed out) PPC unless the question explicitly states constant opportunity cost

Wrong move:

Assuming all outward shifts are uniform

Why:

Shifts are skewed if the change only affects production of one of the two goods

Correct move:

If productivity only improves for one good, only the intercept for that good shifts outwards

6. Quick Reference Cheatsheet

Concept	Location/Change	Key Explanation
Productively efficient	On the PPC	All resources fully employed
Productively inefficient	Inside the PPC	Unused/underemployed resources
Unattainable output	Outside the PPC	Cannot produce with current resources
Movement along PPC	Change on existing curve	Reallocation of resources between goods
Outward shift of PPC	New curve outside original	Increase in productive capacity = economic growth
Inward shift of PPC	New curve inside original	Decrease in productive capacity

When this came up on past exams

AI-estimated based on syllabus patterns — cross-check with official past papers for accuracy. Use only as revision-focus signals.

2023 · 1
Multiple choice on shift of PPC
2022 · 2
Data response on economic growth
2021 · 1
Opportunity cost calculation

What's Next

Mastering PPCs is a critical foundation for almost all other topics in CIE A-Level Economics. This core diagram reappears when studying comparative advantage and international trade, where it is used to illustrate the gains from specialisation and trade between countries. In macroeconomics, shifts of the PPC correspond directly to shifts in long-run aggregate supply, a core concept for analysing economic growth and policy. The distinction between movements and shifts you learned here will help you avoid common mistakes in all future diagram-based questions.