IB DP Economics: Measuring and Managing the Economy (Unit 3.1-3.3) -- Revision Notes

Condensed for the final weeks. For the full explanation, use the Measuring and Managing the Economy study guide.

Measuring economic activity (3.1)

GDP — total output/income of an economy. GNI — additionally accounts for income earned by residents abroad. IB mark schemes credit stating the distinction, not just naming both terms.

Business cycle phases: EXPANSION -> PEAK -> CONTRACTION (recession) -> TROUGH

Recession = falling real output. Slower growth = positive but reduced growth — these are different things, and IB questions frequently test this distinction using data extracts rather than definitions alone.

The AD-AS model (3.2)

The single most important diagram in this unit — nearly every later demand-side and supply-side policy sub-topic is explained via shifting one of AD-AS’s two curves.

Curve	Shifts due to
Aggregate demand (AD)	Its four components: consumption, investment, government spending, net exports
Aggregate supply (AS)	Production costs, productivity, productive capacity (short run vs. long run differ)

Common exam error: shifting the wrong curve — a change in one of AD’s four components shifts AD; a change in costs or productive capacity shifts AS.

Worked example: reading combined data

Real GDP growth falls from 4% to 1% over two years, while inflation rises from 2% to 6%. What does AD-AS suggest?

OBSERVATION: growth slowing sharply + inflation rising -- the
             classic signature of an ADVERSE SUPPLY SHOCK, not a
             demand change.

WHY NOT AD: a rightward AD shift raises BOTH output and price
            level TOGETHER -- doesn't explain slower growth with
            higher inflation.

WHY AS: a leftward shift in short-run AS (e.g. rising input costs)
        raises price level WHILE reducing real output --
        matches both parts of the data at once.

CONCLUSION: negative supply-side shock, not demand-side --
            different policy implications follow.

Distinguish demand-side from supply-side explanations using the DIRECTION of both output and price-level change TOGETHER, not just one variable in isolation — this is exactly what IB data-response questions test.

Macroeconomic objectives (3.3)

1. Economic growth
2. Low unemployment
3. Low and stable inflation
4. Equity in income distribution

(HL extension: calculating a misery index, or interpreting a Lorenz curve/Gini coefficient in more depth.)

Learn these as a fixed set — evaluation questions often ask which objective a policy serves and which it might conflict with (e.g. growth-boosting policy can worsen inflation).

Worked example: a second data-response scenario

A country’s real GDP growth accelerates from 2% to 5% while inflation stays broadly stable at 2%. What does this suggest?

OBSERVATION: growth rising, inflation stable -- output up without
             a matching rise in the price level.

WHY NOT a simple AD shift alone: a large rightward AD shift with
        an unchanged AS curve would normally push the price level
        up too, not leave it stable.

MORE LIKELY EXPLANATION: a rightward shift in (long-run or
        short-run) aggregate supply -- for example from improved
        productivity or new technology -- expanding the economy's
        capacity to produce more output WITHOUT the price pressure
        a demand-side expansion alone would cause.

CONCLUSION: the evidence is more consistent with a positive supply-
        side change (or a combination of AD growth matched by AS
        growth) than with demand-side growth on its own.

Practising both directions – adverse supply shocks (first worked example) and favourable supply-side improvements (this one) – builds genuine fluency in reading combined output/price data rather than only recognising one specific pattern.

Linking 3.1-3.3 to the rest of Unit 3

Sub-topics 3.1-3.3 are the shared foundation the rest of Unit 3 depends on: demand-side policy (fiscal and monetary policy) is explained as shifting AD; supply-side policy is explained as shifting AS; and every policy is ultimately evaluated against the four macroeconomic objectives introduced in 3.3. Treat this content as the vocabulary and diagram fluency the rest of the unit assumes you already have secure, not a self-contained block to revise once and move past.

Key terms

GDP — total output/income within a country. GNI — GDP plus income earned by residents abroad. Business cycle — the recurring pattern of expansion, peak, contraction, trough. Aggregate demand — total planned spending in an economy at each price level. Aggregate supply — total output producers are willing to supply at each price level.

Common mistakes

• Confusing GDP with GNI — state the distinction explicitly, not just both definitions.
• Shifting the wrong curve for a given policy or shock.
• Treating the four macroeconomic objectives as always compatible, when the tension between them (especially growth vs. inflation) is a large part of what’s tested.
• Giving purely theoretical answers without a real, named example — IB rewards specific application (a country’s actual GDP data, an inflation episode, a documented policy conflict) over generic theory.

Building a real-world example bank

Keep two or three up-to-date real-world examples for growth, inflation and unemployment ready for essays and data-response questions — HL and SL papers alike credit accurate, specific application over theory alone, and this is one of the highest-value pieces of preparation for this sub-topic.

Quick self-test

• State the difference between GDP and GNI.
• Name the four phases of the business cycle, with one real-world example of any phase.
• Sketch AD-AS from memory, labelling both curves, equilibrium price level and output.
• Explain what shifts AD vs. what shifts AS.
• Given data showing falling output and falling inflation together, judge whether this looks more like a demand-side or supply-side change, and explain why.

Official syllabus

International Baccalaureate Organization, Diploma Programme Economics guide, published February 2020, updated to October 2020, first assessment 2022, sub-topics 3.1-3.3 — ibo.org.