1.1 Production possibility frontiers: the PPF as a model of scarcity and choice, points on, inside and beyond the curve, opportunity cost along the frontier, the shape of the curve, and shifts representing growth or decline.

What this dot point is asking

OCR wants you to use a production possibility frontier (PPF) to model scarcity, choice and opportunity cost, to interpret points on, inside and beyond the curve, to explain why the curve is usually bowed outward, and to distinguish movements along the curve from shifts of the whole curve.

What a PPF shows

The PPF is the simplest model of scarcity and choice. With quantity of good A on one axis and good B on the other, the frontier is the boundary of what is achievable. Because resources are scarce, an economy cannot produce beyond the frontier; because choices must be made, it must pick a point on (or inside) it.

Points on, inside and beyond the curve

• On the curve: the economy is productively efficient, using all resources to their fullest, so it cannot produce more of one good without producing less of the other.
• Inside the curve: the economy is producing less than it could, which means unemployed or inefficiently allocated resources (for example, a recession with idle factories and workers). The point is achievable but wasteful.
• Beyond the curve: a combination that is currently unattainable with existing resources and technology. It becomes attainable only if the PPF shifts outward.

A move from an inside point to a point on the curve is not economic growth: it is a recovery that uses spare capacity. True growth requires the frontier itself to move.

Opportunity cost along the frontier

On a point on the curve, producing more of one good requires moving along the frontier and giving up some of the other. The amount given up is the opportunity cost. On a straight-line PPF the opportunity cost is constant; on a bowed-out PPF it rises as more of one good is produced.

Why the curve is bowed outward

The PPF is usually concave to the origin because factors of production are not equally productive in both uses. As an economy shifts resources from making manufactured goods to producing food, it first moves the resources best suited to food, then increasingly moves resources that were far better at manufacturing. Each extra unit of food therefore costs more and more manufactured goods, giving rising opportunity cost and the bowed-out shape. (A straight-line PPF assumes resources are perfectly substitutable, which is a useful simplification but rarely realistic.)

Movements versus shifts

The choice between capital goods and consumer goods today affects where the PPF sits tomorrow. Producing more capital goods (investment) now means less current consumption but a larger outward shift later, because the capital stock grows.

Examples in context

• Recession and recovery. During the 2008 to 2009 downturn, UK output fell well inside the PPF as factories and workers stood idle; the recovery moved the economy back toward the frontier without any growth in capacity.
• Investment versus consumption. A developing economy that devotes resources to infrastructure (capital goods) sacrifices current consumption to shift its PPF out faster.
• Technology shocks. Advances such as automation or AI can shift the PPF outward, particularly for goods where the new technology raises productivity most.

Try this

Q1. Explain why a point inside the PPF indicates inefficiency. [3 marks]

• Cue. Resources unemployed or misallocated, so more of one good could be made without giving up the other.

Q2. Explain why a PPF is normally drawn concave to the origin. [4 marks]

• Cue. Factors not equally suited to both goods, so opportunity cost rises as output of one good increases.