SPM Economics common mistakes
SPM Economics · Understand the traps and how to avoid them.
When asked to calculate equilibrium price and quantity, the candidate sets the demand equation equal to zero (or the supply equation equal to zero) instead of setting quantity demanded equal to quantity supplied, then reports a single price as the answer.
The candidate memorises the formula layout but forgets the economic condition behind it: equilibrium means Qd = Qs. Solving 'for the equation' rather than 'for the market condition' feels mathematically complete, so the error is not noticed.
What to do instead
Before any algebra, write the condition in words on the answer line: 'Equilibrium: Qd = Qs'. Substitute both equations, solve for P, then substitute P back into either equation to get Q. Always state both P and Q in the final answer, and check that the result is positive.
The candidate labels a movement along the demand curve as a 'shift' (or vice versa) whenever price changes, drawing a new parallel curve after a price change and calling it an increase in demand.
The candidate confuses the two axes: a change in the good's own price is measured on the vertical axis, so it can only move a point along the existing curve. Textbooks stress 'shift' so heavily that the candidate applies it to every change.
What to do instead
Use a two-question test: (1) Is the change in the good's own price? If yes, movement along the curve. (2) Is it income, tastes, price of related goods, population, or expectations? If yes, shift. Practise by sorting a list of ten events into 'along' versus 'shift' before drawing anything.
When computing price elasticity of demand, the candidate divides the change in quantity by the change in price, or drops the minus sign incorrectly, then classifies a good as elastic when it is inelastic (or mislabels a normal good as inferior).
The candidate remembers 'percentage change over percentage change' but applies it to the wrong pair of variables, and treats the negative sign as an arithmetic slip rather than an economic signal.
What to do instead
Write the formula as Ed = (% change in Qd) / (% change in P) and compute each percentage change as (new - old)/old x 100. Take the absolute value only at the final step and state explicitly '|Ed| > 1 elastic, < 1 inelastic, = 1 unitary'. For income elasticity, keep the sign and interpret positive as normal, negative as inferior.
The candidate explains factor demand and factor supply as if households demand labour and firms supply labour, reversing the roles of households and firms in the labour market, and then gives a backwards explanation of how wages are determined.
In product markets households demand and firms supply, so the candidate carries that pattern over to factor markets without checking who buys and who sells the factor.
What to do instead
Anchor on one sentence: 'Firms demand factors to produce; households supply factors and receive income.' Draw the labour market with firms on the demand side (derived demand from product demand, MRP) and households on the supply side (opportunity cost of leisure). Re-derive wage equilibrium from that diagram every time.
The candidate treats transfer payments, pensions, scholarships, and gifts as factor income, or counts them inside GDP when asked to explain the income approach or the distribution of income.
These flows are received by households and look like income, so the candidate assumes they must be payments for factors of production. The distinction between 'payment for a service rendered' and 'payment without a current service' is not applied.
What to do instead
Apply the test: 'Is something currently produced being paid for?' If no, it is a transfer, not factor income (rent, wages, interest, profit). When using the income approach to GDP, explicitly exclude transfers, and when discussing income distribution, note transfers as redistribution rather than as factor reward.
The candidate defines money by listing its functions but then claims that anything performing a function (for example a credit card, a debit card, or a fixed deposit) is money, and answers questions about money supply by counting credit card limits as part of the money supply.
The functions list is memorised without the underlying properties (generally accepted, legal tender, medium of exchange). Cards are used like money at the till, so the candidate equates method of payment with money itself.
What to do instead
State the definition first: money is anything generally accepted as a medium of exchange and settlement of debt. Then classify: credit cards are a means of deferring payment (a loan), debit cards are an instruction to transfer deposits (the deposit is money), fixed deposits are near money (M2/M3 depending on the definition used). Answer money-supply questions using the stated definition of M1/M2/M3, not intuition.
The candidate explains how a central bank raises the interest rate by saying it 'directly sets all commercial bank lending rates', and describes open market operations as the government borrowing from the public to fund spending.
The candidate collapses three separate actors (central bank, government, commercial banks) into one, so monetary policy and fiscal policy become indistinguishable.
What to do instead
Separate the actors in a three-line table: central bank (controls money supply, policy rate, reserve requirements, open market operations, lending to banks); government (fiscal: taxes, spending, borrowing via securities); commercial banks (set their own rates in response to liquidity and the policy rate). For open market operations, say the central bank buys or sells securities to change bank reserves, not to finance spending.
When asked for policies to reduce unemployment or inflation in Malaysia, the candidate lists only generic instruments ('increase government spending', 'reduce interest rates') without naming the Malaysian institution, the specific tool, or the transmission channel, and without distinguishing demand-pull from cost-push inflation.
The candidate treats the policy chapter as a vocabulary list and never links each instrument to a type of problem. The Malaysian institutional context (Bank Negara Malaysia, Ministry of Finance, specific schemes) is skipped because it feels like extra detail.
What to do instead
For each answer, use a three-part structure: problem type (demand-pull, cost-push, structural, cyclical) -> institution and instrument (e.g. Bank Negara Malaysia raising the OPR; Ministry of Finance raising development expenditure; specific retraining or wage programmes) -> channel and expected effect. Reject any instrument that does not match the diagnosed type.
The candidate answers a balance of payments question by adding the current account and the capital/financial account and calling the total 'the balance of payments surplus', ignoring the reserves line and the sign conventions for inflows and outflows.
The candidate treats the balance of payments like a simple budget total, not realising it is a double-entry system that must balance, so a surplus on one account is offset elsewhere.
What to do instead
Write out the identity: current account + capital and financial account + net errors and omissions + change in reserves = 0. Then answer the actual question: a current account surplus means net lending abroad, matched by outflows in the financial account or reserve accumulation. Practise with a small table of credits and debits and confirm the total is zero.
The candidate explains a currency depreciation by saying 'exports become cheaper so exports rise and imports fall, so the current account improves' and stops there, without mentioning the price elasticity condition or the effect on import costs and inflation.
The candidate reproduces the one-line textbook chain without the qualifications, so the answer is one-directional and cannot earn marks for analysis or evaluation.
What to do instead
Give the full chain and its conditions: depreciation lowers export prices in foreign currency and raises import prices in domestic currency; the trade balance improves only if the Marshall-Lerner condition holds (sum of elasticities > 1) and after a J-curve lag; also note the cost-push inflationary pressure from dearer imports. Include at least one counter-effect in every depreciation answer.