Cambridge International AS and A Level Economics: Growth, output gaps, the business cycle and policies (9708)

This guide covers outcomes 9.2.1 to 9.2.4 of the Cambridge International AS & A Level Economics 9708 syllabus for examination in 2026, 2027 and 2028. Topic 9 is A Level content, so it is not examined at AS. The syllabus treats AS content as assumed knowledge for A Level Papers 3 and 4. Every country, firm and figure below is invented for illustration and is not a real statistic.

Use the Cambridge A Level Economics hub and printable checklist to track coverage, then the revision notes and the practice questions. The AS-level economic growth guide covers measuring growth. To find weak spots first, take a free 10-minute diagnostic.

What this guide covers

Outcome	What you must be able to do
9.2.1	Distinguish actual growth from potential growth in national output
9.2.2	Explain positive and negative output gaps
9.2.3	Explain the phases and causes of the business (trade) cycle, and the role of automatic stabilisers
9.2.4	Explain policies to promote economic growth and assess their effectiveness

Inclusive and sustainable growth (9.2.5 and 9.2.6) are separate outcomes and are not taught here.

9.2.1 Actual growth and potential growth

Actual growth is the percentage change in real national output (real GDP) from one period to the next. It is what is measured and reported. Potential growth is the percentage increase in the economy’s productive capacity: the output it could produce if resources were fully and efficiently used. In the AD/AS model, actual growth is a rise in real GDP: a rightward shift of aggregate demand along short-run aggregate supply. Potential growth is a rightward shift of long-run aggregate supply. On a production possibility curve, actual growth is a move from inside the curve towards it, and potential growth is an outward shift of the whole curve.

The two can differ. With spare capacity, a rise in aggregate demand raises actual output without changing capacity. At capacity, extra demand cannot lift actual output for long. Only an increase in the quantity or quality of factors of production, or in productivity, raises potential output.

Worked example 1. Country K is invented. Its potential output grows at 3% a year from 1,000 units. Actual output and the gap against potential (output gap, defined in the next section) are:

Year	Actual output	Potential output	Actual growth	Gap (actual minus potential)
1	960	1,000.0		−40.0
2	1,010	1,030.0	5.2%	−20.0
3	1,085	1,060.9	7.4%	+24.1
4	1,070	1,092.7	−1.4%	−22.7

Actual growth of 5.2% in year 2 is above potential growth of 3%, so spare capacity is used up. Growth of 7.4% in year 3 cannot last, because output has overshot capacity. In year 4 actual output falls while potential output still rises by 3%.

9.2.2 Positive and negative output gaps

An output gap is the difference between actual output and potential output.

output gap (% of potential) = (actual output − potential output) / potential output × 100

A positive output gap means actual output is above potential. Resources are used beyond their normal sustainable intensity. Firms use overtime and run machines hard, and unemployment is below its natural rate. The chain: demand exceeds sustainable supply, firms raise prices, labour shortages push up wages, costs rise and inflation accelerates. Imports are pulled in too. A positive gap is sometimes called an inflationary gap.

A negative output gap means actual output is below potential. There is spare capacity: idle machines, cyclical unemployment and weak investment. Firms have little power to raise prices and wage growth is subdued, so inflation tends to fall. Unemployment is above its natural rate. The output that could have been produced is lost permanently. A persistent gap can reduce potential output itself, as firms cut investment and workers lose skills.

Worked example 2. Using year 3 of country K: (1,085 − 1,060.9) / 1,060.9 × 100 = +2.27%, a positive gap. For year 1: (960 − 1,000) / 1,000 × 100 = −4.0%, a negative gap.

Worked example 3 (a gap can narrow while both grow). In country M, actual output rises from 640 to 672 (5.0%) and potential output rises from 700 to 724.5 (3.5%). Gap before: (640 − 700) / 700 = −8.57%. Gap after: (672 − 724.5) / 724.5 = −7.25%. The gap narrows because actual growth (5.0%) is above potential growth (3.5%). It does not close, so spare capacity remains.

Difficulty in measurement. Potential output cannot be observed. It is estimated from trends in labour, capital and productivity, and estimates are revised, so the size of a gap is uncertain. If a supply shock damages capacity, the same output may become a positive gap.

9.2.3 The business (trade) cycle

The business cycle is the pattern of fluctuations of actual growth around the long-run trend of potential growth. Output does not grow smoothly. It speeds up, slows, falls and recovers.

Phases. Textbooks name the phases slightly differently, but a standard description is:

• Boom (peak): growth is fast, output is above trend, unemployment is low and inflation tends to rise. The output gap is positive.
• Downturn (slowdown): growth slows and may turn negative. Demand weakens, firms cut investment and stocks build up.
• Recession (trough): output falls, unemployment rises and inflation falls. A common working definition of recession is two consecutive quarters of negative growth. The trough is the lowest level of output.
• Recovery: growth returns, firms hire, and the output gap closes.

Worked example 4. Country L has annual growth of 4.1%, 2.0%, −0.8%, −1.5%, 1.2%, 3.6% and 4.4% in years 1 to 7. An index of real GDP starting at 100 runs: 104.1, 106.18, 105.33, 103.75, 105.0, 108.78, 113.56. Output peaks at the end of year 2 and falls in years 3 and 4. It reaches its trough at the end of year 4 (103.75). Growth turns positive in year 5, so recovery begins, but output (105.0) is still below the earlier peak (106.18). Growth can recover before the level of output does, so the gap may stay negative for a while.

Causes of the cycle. Cycles come from shifts in demand, shifts in supply and the way the economy amplifies them.

• Changes in confidence and expectations. Optimism raises consumption and investment. Pessimism cuts them. Expectations can reinforce themselves.
• Investment and the accelerator. Investment depends on changes in output. A slowdown in the growth of demand can cause a large fall in investment, which feeds back through the multiplier.
• The multiplier. Any change in spending is magnified, so a fall in one component of aggregate demand causes a larger fall in output.
• Credit and interest rates. Easy credit fuels booms. Higher rates or tighter lending can trigger a downturn.
• External shocks. Changes in world demand alter exports. Commodity price changes shift costs and short-run aggregate supply.
• Stock cycles and supply shocks. Firms over-order stocks in a boom then cut orders. New technology or a natural event can shift aggregate supply.
• Policy. Mistimed stimulus or tightening, because of time lags, can add to fluctuations.

Automatic stabilisers are features of the tax and benefit system that reduce fluctuations in aggregate demand without a new government decision. In a boom, incomes and spending rise, so tax receipts rise (especially with progressive income taxes) and benefit payments fall. This withdraws demand. In a downturn tax receipts fall and benefit payments rise, supporting disposable income. The budget moves towards deficit in a downturn and towards surplus in a boom.

Worked example 5. In an invented economy, mps = 0.10, marginal rate of tax withdrawal = 0.20 and mpm = 0.20. The multiplier is 1 / (0.10 + 0.20 + 0.20) = 2.0. A fall in investment of 20 reduces income by 20 × 2.0 = 40. If income-linked taxes were absent, the multiplier would be 1 / (0.10 + 0.20) = 3.33 and income would fall by 66.7. Taxes that rise and fall with income make the multiplier smaller and the swings milder. In the downturn, tax revenue falls by 40 × 0.20 = 8. If unemployment benefit rises by 4, the budget balance worsens by 12, which supports demand without any new decision.

Limits. Stabilisers reduce fluctuations but do not remove them or close a large gap. They are stronger with progressive taxes and generous benefits. They worsen the budget deficit in a recession, can slow a recovery by holding back disposable income, and do not change the trend rate of growth.

9.2.4 Policies to promote growth and their effectiveness

Separate policies for actual growth (demand side, mainly useful when there is a negative gap) from policies for potential growth (supply side, raising capacity).

Demand-side policies.

• Expansionary fiscal policy: higher government spending or lower taxes raise aggregate demand. The effect is multiplied.
• Expansionary monetary policy: lower interest rates or increased money supply encourage borrowing, consumption and investment, and may reduce the exchange rate.
• Exchange rate policy: a lower rate can raise net exports.

Supply-side policies.

• Education, training and health: raise labour productivity.
• Infrastructure and investment incentives: transport, energy and communications lower costs and raise capital per worker.
• Research and development support and technology transfer: raise productivity.
• Tax and benefit reform: lower marginal taxes or tighter benefits to encourage work and enterprise.
• Competition policy, deregulation, privatisation and trade liberalisation: pressure firms to cut costs and allow resources to move to productive uses.
• Labour market reforms and encouraging inward investment or migration: raise the quantity of factors.

Worked example 6 (policy for a negative gap). Economy N has potential output of 2,000 and actual output of 1,900, a gap of −5.0%. The marginal rate of tax is 0.20, mps is 0.10 and mpm is 0.10, so the multiplier is 1 / 0.40 = 2.5. An extra 30 of government spending raises output by 30 × 2.5 = 75, to 1,975. The gap narrows to −1.25%. To close it fully, the required rise in output is 100, so government spending must rise by 100 / 2.5 = 40. Suppose instead the economy begins with a positive gap: output is 2,060 (+3.0%). The same 30 gives 2,135, a gap of +6.75%. The stimulus now causes inflation, not growth. Policy works only if it is matched to the gap.

Worked example 7 (supply-side). If the labour force grows by 1.2% and output per worker rises 2.5%, potential output grows by (1.012 × 1.025) − 1 = 3.73%. Adding the rates gives a close 3.7%.

Effectiveness. Use these criteria and apply them to the context.

• Time lag: demand policies act in months, but supply-side policies can take years, since education pays back only as people join the workforce.
• Size of the gap: expansionary demand policy is effective with a large negative gap but inflationary with a positive gap.
• Permanence: demand policies do not raise capacity. Supply-side policies raise potential growth but do not help a deep recession.
• Cost and crowding out: spending has an opportunity cost, and funding by borrowing can raise interest rates and crowd out private investment.
• Other objectives: growth can conflict with inflation, the current account (imports rise) and the environment.
• Uncertainty: the multiplier and the size of the gap are estimates.

A strong answer reaches a judgement: supply-side policy gives more durable growth, demand policy is quicker in a recession, and the best mix depends on the size and cause of the gap.

Common errors

• Saying potential growth rises because aggregate demand rises. Demand moves actual output, not capacity.
• Calculating the gap as actual minus potential divided by actual. Divide by potential.
• Describing stabilisers as a government decision. They work automatically.
• Listing policies without judging effectiveness.

Official syllabus

Cambridge International AS & A Level Economics (9708), syllabus for examination in 2026, 2027 and 2028, published by Cambridge University Press & Assessment (Cambridge International Education), sections 9.2.1 to 9.2.4.