amazon.co.ukMacroeconomics: AD-AS and Objectives
A* revision for GDP measurement, the circular flow, AD components, SRAS and LRAS, AD-AS equilibrium, output gaps and macroeconomic objectives for AQA 7136, Edexcel A 9EC0 and OCR H460.
🎯 Learning Objectives
- Calculate real GDP and the GDP deflator from nominal data, and evaluate GDP as a measure of living standards
- Explain the circular flow of income, injections and withdrawals, and derive the multiplier
- Analyse the determinants of C, I, G and (X − M) with accurate chains of reasoning
- Draw SRAS, classical LRAS and Keynesian LRAS, and shift each correctly in response to cost and demand shocks
- Determine macroeconomic equilibrium and interpret negative and positive output gaps
- State the four main macroeconomic objectives with current UK data
- Evaluate conflicts between macroeconomic objectives using spare capacity, elasticities and credibility
📋 Key Definitions and Core Concepts
GDP: The total value of goods and services produced within an economy in a period, measurable by expenditure, income or output methods.
Real GDP: Nominal GDP adjusted for inflation using the GDP deflator: (nominal ÷ deflator) × 100.
GDP deflator: (Nominal GDP ÷ real GDP) × 100: the implicit price level of all domestically produced output.
Aggregate demand (AD): Total planned spending on domestic output at each price level: AD = C + I + G + (X − M).
Aggregate supply (AS): Total planned output of firms at each price level; SRAS slopes up because some costs are sticky, LRAS reflects productive capacity.
Circular flow of income: The flow of income and spending between households and firms, with injections (I, G, X) and withdrawals (S, T, M); equilibrium where injections = withdrawals.
Multiplier: The ratio of the final change in real GDP to the initial change in an injection: k = 1/(1 − MPC) or 1/MPW.
Negative output gap: Actual output below potential output: spare capacity, demand-deficient unemployment, downward pressure on inflation.
Full-employment output (Yf): The level of output at which the labour market is at the natural rate of unemployment; the classical LRAS is vertical here.
Sticky wages: Nominal wages that adjust slowly downwards because of contracts, minimum wages, morale and union resistance — the basis of the upward-sloping SRAS and Keynesian LRAS.
Measuring economic activity: GDP, real vs nominal, limitations
GDP — the total value of goods and services produced in an economy in a period — can be measured three ways, which must equal by construction: the expenditure method (C + I + G + (X − M)), the income method (wages, rents, interest, profits), and the output method (value added by sector). Real GDP = (nominal GDP ÷ GDP deflator) × 100 — it strips out inflation to measure volume. The GDP deflator = (nominal ÷ real) × 100; the worked example below shows the calculation. GDP per capita adjusts for population; GNI adds net income from abroad (important for Ireland, where GDP overstates living standards because of multinational profit flows).
Limitations of GDP as a measure of living standards (a guaranteed essay/data-response theme): it ignores the hidden/shadow economy (undeclared work); non-market activity (housework, volunteering); income distribution (average vs typical — median income can fall while mean rises); quality and composition of output; externalities (pollution, congestion are not deducted); leisure; and it is a flow not a stock — a country can raise GDP by depleting resources. Alternative/complementary measures: HDI (see the International topic), Green GDP adjustments, measures of subjective wellbeing (the ONS four wellbeing questions), and the OECD Better Life index.
Data anchors: UK nominal GDP is roughly £2.7 trillion (2024); real GDP fell about 11% in 2020 (the largest peacetime collapse on record) and regained its pre-pandemic level only in 2022; growth since has been sluggish (roughly 0.3–1% a year), well below the pre-2008 trend of 2–2.5%. Exam technique: when given nominal and real figures, always compute the deflator and interpret it as the implicit price level — then link to CPI divergence if asked about inflation measurement.
The circular flow of income and aggregate demand
The circular flow of income: households supply factors of production to firms and receive factor incomes, which they spend back on firms' output. Withdrawals (leakages): saving (S), taxation (T), imports (M). Injections: investment (I), government spending (G), exports (X). National income is in equilibrium when injections = withdrawals; if injections exceed withdrawals, income rises (expansion); if withdrawals exceed injections, income contracts. This frame explains why the multiplier works and why trade deficits drain demand.
AD = C + I + G + (X − M) — total planned spending on domestic output at each price level; AD slopes downward because of the wealth effect (higher price level cuts real balances), the interest-rate effect (higher prices raise money demand and rates) and the exchange-rate effect (higher prices cut competitiveness). UK composition (approximate): C ≈ 60–63% of GDP — the largest and most stable component; I ≈ 17% — the most volatile (accelerator effects, confidence); G ≈ 18–20% (current plus capital spending); (X − M) is a small net figure but both flows are large (exports ≈ 30% of GDP).
Determinants of each component (memorise the chains): C — disposable income, wealth (house prices), interest rates (saving return vs borrowing cost), confidence, credit availability; I — profit expectations/“animal spirits” (Keynes), interest rates (hurdle rate), accelerator (demand growth), corporation tax, spare capacity, credit; G — fiscal policy decisions; X − M — real exchange rate, world income, relative inflation, non-price competitiveness and quality. Diagram description: axes price level (vertical) and real output (horizontal); AD downward-sloping; a fall in any component shifts AD left from AD1 to AD2, moving equilibrium down the SRAS curve — lower price level, lower real output, a negative output gap and rising cyclical unemployment.
Aggregate supply: SRAS, classical LRAS and Keynesian LRAS
SRAS is upward-sloping because some input costs (notably wages on fixed contracts, and other contracted prices) are sticky in the short run: a higher price level raises firms' margins, so output expands. SRAS shifts left when costs rise (oil, imported inputs, a depreciation raising import prices, wage settlements above productivity) and right when costs fall or productivity improves.
The classical LRAS is vertical at the full-employment level of output (Yf): in the long run wages and prices are fully flexible, markets clear, and output returns to Yf regardless of AD — the economy is self-correcting; extra AD raises only the price level. The Keynesian LRAS is reverse-L-shaped or upward-sloping: at low output (deep recession) it is flat, because spare capacity lets output rise without inflation; at high output it turns vertical as capacity binds. Keynesians argue wages are sticky downwards (contracts, minimum wage, morale, union resistance), so a fall in AD causes prolonged demand-deficient unemployment rather than instant wage/price adjustment.
Diagram descriptions to memorise: (1) Classical: axes price level/real output; vertical LRAS at Yf; AD1→AD2 right shift moves equilibrium up LRAS — price level rises, output unchanged. (2) Keynesian: flat LRAS at low output; AD right shift raises output with little or no price rise (spare capacity absorbed); near the vertical section the same shift is mostly inflation. (3) SRAS left shift: costs rise (oil shock) → SRAS1→SRAS2 left → higher price level, lower output — stagflation.
Assessment (which view fits the evidence?): the Keynesian view explains the medium run better — after 2008 and again after 2020, output gaps and elevated unemployment persisted for years, inconsistent with rapid classical self-correction; policy at the zero lower bound failed to restore full employment quickly. The classical view has force in the very long run: output did eventually recover as wages adjusted relatively and capital was reallocated; and stimulus near full capacity causes inflation rather than output (2021–22). Most economists accept a hybrid: the speed of self-correction depends on wage/price flexibility — this “depends on” judgement is the A* conclusion.
AD-AS equilibrium, output gaps and macroeconomic objectives
Macroeconomic equilibrium: where AD intersects AS (SRAS in the short run; LRAS in the long run). If equilibrium output Y1 sits below potential output Yf there is a negative output gap — spare capacity, demand-deficient (cyclical) unemployment, downward pressure on inflation. If Y1 > Yf there is a positive output gap — overheating, demand-pull inflation, pressure on the current account as imports rise. Diagram description: mark Yf with a vertical dashed line; equilibrium left of it = negative gap (shade the distance); right of it = positive gap. Gaps close via self-correction (wage/price adjustment shifting SRAS) or policy (shifting AD).
The four main UK macro objectives (AQA 4.2.1, Edexcel Theme 2.6): (1) sustainable economic growth — rising real GDP consistent with capacity, roughly 2–2.5% trend historically, though potential growth is now estimated near 1.5% by the OBR; (2) low and stable inflation — the 2% CPI target ±1 percentage point, set by HM Treasury and pursued by the Bank of England; (3) low unemployment — full employment at the natural rate (frictional + structural only), UK unemployment around 4–4.5% in 2024–25; (4) equilibrium in the balance of payments — broadly, a sustainable current account (the UK has run deficits of roughly 3–4% of GDP, financed by financial inflows). Secondary objectives: equitable income distribution, sound government finances, balanced regional growth, environmental sustainability.
Conflicts between objectives (the core evaluation theme): growth vs inflation (AD expansion into capacity → demand-pull inflation — the Phillips-type trade-off); inflation vs unemployment (disinflation raises unemployment in the short run); growth vs the current account (income growth pulls in imports); growth vs government finances (stimulus raises borrowing; austerity slows growth); growth vs the environment (GDP growth raises emissions absent decoupling). Exam technique: 25-mark essays on objectives almost always ask you to weigh a benefit against a conflict — structure as “objective A improved, but at the cost of objective B, and the size of the trade-off depends on [elasticities, spare capacity, credibility]”.
The multiplier and national income determination
The multiplier (k) is the ratio of the final change in real GDP to the initial change in an injection: k = 1 / (1 − MPC) in the simple two-sector model, or more fully k = 1 / MPW where MPW (the marginal propensity to withdraw) = MPS + MPT + MPM. Process: an initial £50bn injection is paid to construction firms and workers, who spend 80% (with MPC = 0.8); those recipients spend 80% of that, and so on in a geometric series converging to £250bn (see the worked example below). The reverse also holds — the reverse multiplier: withdrawal of spending (fiscal austerity, a fall in exports) shrinks GDP by a multiple of the initial change, which is why 2010–13 Eurozone austerity deepened recessions.
Size in practice: the UK's open economy has large leakages (high MPM, progressive taxation), so OBR central estimates of fiscal multipliers are around 0.6–1 (higher — above 1 — when the economy has spare capacity and monetary policy is accommodative; lower near full employment when the Bank of England offsets the stimulus). The simple 1/(1−MPC) formula overstates: it ignores imports, taxes, crowding out, time lags and capacity constraints.
Uses in essays: the multiplier magnifies the effect of any AD shock — oil price rises, confidence collapses, export slumps — and magnifies policy responses; it interacts with the accelerator (investment responds to the growth of demand, not its level, so a slowing multiplier can trigger an investment slump). Evaluation points to deploy: the multiplier is larger when MPC is high (lower-income recipients spend more — targeting transfers at low-income households raises k), when spare capacity exists, and when leakages are small; it is smaller in open economies, near capacity, and if households save transfers (Ricardian-style caution) or the central bank offsets. Data anchor: UK MPC around 0.6–0.9 depending on income group; MPM is high enough that the open-economy multiplier is well below the closed-economy formula.
💡 Worked Example
Exam-style: Using an AD/AS diagram, analyse the effect of a rise in world oil prices on the price level and real output, and evaluate how the outcome differs according to the shape of the long-run aggregate supply curve. (AQA 7136 Paper 2 style, 15 marks)
Mark-scheme logic: Mark logic: [AO1] define the shock and the AD/AS framework; [AO2] show the shift with an accurate diagram description; [AO3] chain of reasoning; [AO4] evaluate using LRAS shapes and evidence. Analysis: oil is a key input (transport, energy, petrochemicals). A sharp rise raises firms' costs of production, shifting SRAS left from SRAS1 to SRAS2. With AD unchanged, the new equilibrium is at a higher price level (cost-push inflation) and lower real output — stagflation: rising inflation with falling output and rising cyclical unemployment. The size of the shift depends on the oil intensity of production and on firms' ability to substitute. Evaluation: under the classical LRAS (vertical at Yf), output returns to Yf in the long run as wages and prices adjust — the shock is temporary and self-correcting; only the price level is permanently higher. Under the Keynesian LRAS, if the economy had spare capacity the SRAS shift may be partly absorbed; if second-round effects occur (wage demands chasing higher prices, expectations de-anchoring), the shift becomes persistent and the loss larger. Evidence: the 1970s oil shocks produced persistent stagflation (UK inflation 24% in 1975), while the 2022 shock raised UK CPI to 11.1% but with unemployment only ~3.6% — expectations were better anchored by an independent central bank, so the second-round effects were weaker. Judgement: the outcome depends on the persistence of the shock, wage-price flexibility and the credibility of monetary policy.
❓ Practice Questions & Mark Schemes
The government increases infrastructure spending by £50 billion. The marginal propensity to consume (MPC) is 0.8. Calculate the size of the multiplier and the total rise in real GDP, and explain why the actual impact may be smaller.
Answer: k = 1/(1 − MPC) = 1/(1 − 0.8) = 5. Total rise = £50bn × 5 = £250bn. Process: the initial £50bn is paid to construction firms and workers, who spend 80% (£40bn); recipients spend 80% of that (£32bn); the geometric series converges to £250bn. Evaluation: the actual impact is smaller because the simple formula ignores leakages — imports (MPM), taxation (MPT) and saving (MPS): the open-economy multiplier is 1/MPW where MPW = MPS + MPT + MPM; borrowing may raise interest rates and crowd out private investment; time lags delay the feed-through; and near full capacity (LRAS vertical) the extra AD raises prices rather than output. OBR central estimates for UK fiscal multipliers are around 0.6–1, so a realistic impact is £30–50bn, not £250bn.
Using an AD/AS diagram, analyse how a fall in business confidence affects the macroeconomy, and evaluate one policy the government or central bank could use to offset the effects.
Answer: Investment depends on expectations (Keynes' animal spirits); weak expected demand makes firms postpone or cancel capital projects, so I falls and AD shifts left from AD1 to AD2. With an upward-sloping SRAS, the price level falls and real output falls — a negative output gap, rising cyclical unemployment; the reverse multiplier deepens the fall as incomes drop. Policy: the central bank cuts the base rate — lowering borrowing costs and mortgage repayments, raising investment incentives, and possibly depreciating the currency (hot-money outflows) to help net exports; AD shifts back right. Evaluation: monetary policy may fail in a deep slump (liquidity trap, low confidence — firms will not borrow at any rate); long and variable lags (12–18 months); but the policy conflict is low here since inflation is falling below target. Fiscal expansion is an alternative but risks crowding out and higher debt. Judgement: rate cuts for moderate downturns; coordinated monetary and fiscal expansion for severe recessions.
Explain the difference between the classical and Keynesian views of the long-run aggregate supply curve, and assess which view better explains the economy's behaviour after a recession.
Answer: Classical LRAS: vertical at Yf — wages/prices fully flexible, markets clear, output self-corrects to Yf regardless of AD; extra AD raises only prices. Keynesian LRAS: reverse-L shaped — flat at low output (spare capacity absorbs demand without inflation), vertical near capacity; wages are sticky downwards (contracts, minimum wage, morale, unions), so falling AD causes prolonged demand-deficient unemployment. Assessment: the Keynesian view explains the medium run better — after 2008 (UK and Eurozone) output gaps and unemployment persisted for years, inconsistent with rapid classical self-correction; zero-lower-bound monetary policy failed to restore full employment quickly. The classical view has force in the very long run: output did recover as wages adjusted and capital reallocated; and stimulus near capacity causes inflation (2021–22). Judgement: a hybrid — the speed of self-correction depends on wage/price flexibility; Keynesian for the medium run, classical for the very long run.
Nominal GDP is £2.2 trillion and real GDP is £2.0 trillion. Calculate the GDP deflator and interpret it.
Answer: Deflator = (nominal ÷ real) × 100 = (2.2 ÷ 2.0) × 100 = 110. Interpretation: the implicit price level of domestic output has risen 10% since the base year (index 100); of the 10% nominal growth, 10 percentage points is inflation and 0% real growth — real GDP is unchanged. Extension: the deflator covers all domestically produced output (broader than CPI, which covers a consumer basket including imports); if the deflator rises faster than CPI, export-sector or investment-good prices are driving inflation rather than consumer prices.
Using a diagram, analyse a recessionary gap and explain two ways it could be closed.
Answer: Recessionary (negative output) gap: equilibrium Y1 left of the vertical Yf line — spare capacity, cyclical unemployment, inflation below target. Diagram: AD1 intersecting SRAS at Y1 < Yf; shade the gap. Closure 1 — demand side: expansionary fiscal (higher G, lower T) or monetary policy (lower rates, QE) shifts AD right to AD2, moving equilibrium to Yf; speed depends on multipliers and lags; risk of inflation if the gap is mis-estimated. Closure 2 — supply side: policies shifting LRAS/SRAS right (training, infrastructure, deregulation) raise Yf towards actual output — sustainable but slow (years, a generation for education). Evaluation: demand management works faster but raises debt and can overshoot; supply-side is durable but cannot solve a demand-deficient gap quickly; often the gap closes by self-correction (wage flexibility) — classical view — though evidence after 2008 shows this is slow. Judgement: severity and speed required determine the mix.
Explain why fiscal policy may be less effective in an open economy, and evaluate one offsetting consideration.
Answer: In an open economy, fiscal stimulus leaks abroad: a high marginal propensity to import means much of the extra spending buys foreign goods, so the domestic multiplier is 1/MPW and small. Additionally, in a floating exchange rate regime, borrowing may raise interest rates, attracting hot-money inflows that appreciate the currency, making exports less competitive (X − M falls), offsetting the fiscal expansion — the Mundell–Fleming logic. Offsetting consideration: if the economy has deep spare capacity and monetary policy is accommodative (rates held low), crowding out and appreciation are limited — multipliers can exceed 1; targeted transfers to liquidity-constrained households have high MPC and less import leakage. Judgement: openness reduces fiscal potency, but the size of the effect depends on spare capacity, the exchange-rate regime and the MPC of recipients.