IB Economics HL common mistakes
IB Economics HL · Understand the traps and how to avoid them.
In Paper 1 essays, candidates define a term and then immediately describe a real-world example or list textbook features, never drawing a labelled diagram or using it to explain the mechanism (e.g., explaining how a negative externality of production shifts MSC away from MPC).
Under time pressure candidates treat 'explain' as 'describe' and reproduce memorised definitions; many have practised diagrams only in isolation, so they do not habitually link diagram labels to the causal chain the question demands.
What to do instead
Before writing, sketch the required diagram and label axes, curves, and equilibrium points. Then write the explanation as a sequence that names each curve and the movement between equilibria (e.g., 'MPC lies below MSC because the firm does not pay the spillover cost; at free-market output Q1, MSC exceeds MSB, so the shaded welfare loss is the triangle between the curves'). Practise past-paper 'explain' commands by forcing at least one diagram plus two sentences interpreting it.
In Paper 3 calculation questions, candidates compute a value (e.g., price elasticity of demand, a multiplier effect, or a change in national income) but give no units, wrong sign, or fail to state the economic interpretation of the number.
Candidates focus on arithmetic and treat the final number as the answer; they often do not know that PED is conventionally negative and that the magnitude determines revenue implications, or that a multiplier of 2.5 means a $1bn injection raises GDP by $2.5bn.
What to do instead
Adopt a fixed three-line answer format for every calculation: formula, substitution with units, and a one-sentence interpretation ('PED = -0.4, so demand is price inelastic; a price rise raises total revenue'). Practise converting every calculation into an economic statement, and check sign conventions for PED, YED, and XED before moving on.
When evaluating market structures, candidates assert that a monopoly is 'bad' or an oligopoly is 'competitive' without comparing outcomes against specific criteria (allocative efficiency, productive efficiency, dynamic efficiency, consumer surplus, or price/output relative to the competitive benchmark).
Textbook summaries present structures as a ranked list, and candidates memorise verdicts rather than the criteria. They also confuse the model assumptions (e.g., a monopoly facing a downward-sloping demand curve and MR below AR) with the evaluation.
What to do instead
Structure every evaluation as: criterion, model prediction, real-world caveat, judgement. For example: 'Allocatively, a profit-maximising monopoly sets MR = MC, so P > MC and there is deadweight loss; however, if the firm uses supernormal profit for R&D, dynamic efficiency may offset this, and contestability (low entry barriers) can discipline pricing even with one firm.' Name the criterion explicitly in each sentence.
In macro policy questions, candidates recommend 'increase government spending' or 'cut interest rates' without specifying the transmission mechanism, the time lags, or the state of the economy (recessionary vs inflationary gap, near-full capacity).
Policy answers are memorised as slogans; candidates skip the chain from instrument to target variable and ignore that the same policy has different effects depending on the output gap and the slope of the AS curve.
What to do instead
Write each policy as a chain: instrument → intermediate variable → aggregate demand component → output/price level. Example: 'Cutting the policy rate lowers commercial lending rates, raises investment and consumption, shifting AD right; with spare capacity the main effect is real output, but near full employment it mostly raises the price level.' State the assumed output gap and one lag or constraint.
On the Phillips curve and monetarist/Keynesian debates, candidates draw a single downward-sloping Phillips curve and conclude there is a permanent inflation–unemployment trade-off, ignoring expectations and the long-run vertical curve.
The short-run curve is the most visually memorable diagram, and candidates do not distinguish short-run from long-run, or adaptive from rational expectations, so they treat a temporary relationship as permanent.
What to do instead
Always draw both: a short-run Phillips curve (SRPC) with the long-run vertical curve at the natural rate of unemployment. Explain that expansionary policy can move along the SRPC only if inflation expectations are unchanged; once expectations adjust, the SRPC shifts up and unemployment returns to the natural rate. Use one concrete episode-style example of expectations shifting the curve.
In trade and protectionism answers, candidates list tariffs, quotas, and subsidies as 'reducing imports' without analysing who gains and loses (consumers, domestic producers, government, foreign exporters) or the welfare loss on a diagram.
Protectionism is taught as a list of instruments; candidates rarely practise the welfare decomposition (consumer surplus loss vs producer surplus and tariff revenue gain) and so produce one-sided 'protects jobs' answers.
What to do instead
For each instrument, draw the domestic market with world price and show the price rise, quantity changes, and shaded areas for consumer loss, producer gain, government revenue, and deadweight loss. Then write a two-sided judgement naming the affected groups and whether the instrument is a tariff (revenue-raising) or quota (rents to licence holders).
In development economics, candidates equate development with GDP per capita growth and evaluate aid or debt strategies without using multidimensional measures (HDI, Gini, MPI) or distinguishing growth from development.
GDP is the most familiar measure and candidates default to it; they also treat 'aid is good/bad' as a debate to be memorised rather than assessed against conditions (governance, absorptive capacity, tied aid, moral hazard).
What to do instead
Open every development answer by distinguishing growth (rising real output) from development (improvements in living standards, health, education, and distribution) and cite at least two measures with their limitations (e.g., HDI ignores inequality; Gini ignores absolute income). Evaluate aid by conditions: is it tied, does the recipient have absorptive capacity and accountable institutions, and does it crowd out domestic investment?
In exchange-rate and balance-of-payments questions, candidates describe a depreciation as automatically 'improving the trade balance' without invoking the Marshall–Lerner condition (sum of export and import demand elasticities greater than one) or the J-curve.
The depreciation-improves-exports story is intuitive and memorable, so candidates omit the elasticity precondition and the short-run adjustment path.
What to do instead
State the condition explicitly: a depreciation improves the trade balance only if |PED exports| + |PED imports| > 1. Then explain the J-curve: in the short run, contract prices are fixed, so the value of imports may rise before volumes adjust, worsening the balance before it improves. Apply it to a specific case with elastic vs inelastic demand.
For the Internal Assessment, candidates choose a news article that reports a price change or policy but contains no economic phenomenon to analyse, then write a summary of the article with definitions appended rather than an argument using a diagram and evaluation.
Candidates pick articles for topical interest or because they are easy to summarise; they do not check whether the article supports a diagram-based explanation with identifiable stakeholders and a defensible judgement.
What to do instead
Select an article only if it contains a clear economic concept (a price movement, externality, policy change, or market structure) that maps to a diagram you can draw. Structure each commentary as: article link and concept, diagram with explanation of the mechanism, application to the specific market and stakeholders, evaluation of assumptions and alternatives, and a judgement. Draft the diagram before writing the commentary.
Across all papers, candidates answer the command word imprecisely: they 'evaluate' by listing points without a judgement, or 'discuss' by giving only one side, and they ignore the mark allocation when deciding how much to write.
Command words are treated as interchangeable, and candidates have not internalised that 'evaluate' and 'discuss' require a weighed conclusion, while 'calculate' or 'define' need brevity. Time pressure then encourages writing everything they know.
What to do instead
Underline the command word and the mark allocation before planning. For 'evaluate' or 'discuss', plan at least two arguments per side plus an explicit conclusion that states which effect dominates and why. Allocate minutes roughly in proportion to marks, and finish every extended answer with a sentence beginning 'Overall, the extent to which... depends on...' to force a judgement.