QCAA Economics common mistakes
QCAA Economics · Understand the traps and how to avoid them.
Describing a movement along the demand or supply curve and a shift of the curve as if they were the same event, so that a change in price is said to 'shift' demand.
The two effects are taught side by side and both are drawn with the same axes, so under exam pressure candidates reach for the word 'shift' whenever they see a change, without checking whether the cause was the good's own price or a non-price factor.
What to do instead
Before writing, name the cause of the change out loud. If the cause is the good's own price, write 'movement along' and refer to expansion or contraction; if it is a non-price factor (income, tastes, prices of substitutes or complements, expectations, number of buyers), write 'shift' and specify left or right. Practise sorting a list of ten causes into the two columns before writing any explanation.
Drawing a supply and demand diagram with unlabelled axes, no equilibrium price and quantity marked, no arrows showing the direction of change, and no distinction between the original and new curves.
Candidates treat the diagram as decoration rather than as evidence, so they draw it quickly at the start of the answer and never return to it; they also run out of time and cut labelling to save seconds.
What to do instead
Use a fixed checklist every time: label both axes with the variable and the unit, label every curve (D, D1, S, S1), mark Pe and Qe, draw arrows from the old to the new equilibrium, and write a one-sentence caption stating what moved and why. Rehearse the checklist until it takes under a minute.
Confusing a change in the price of a good with a change in the general price level, and therefore applying microeconomic supply and demand analysis to a macroeconomic question about inflation.
Both topics use the language of 'price' and 'demand', and the inflation topic is often revised immediately after the market topic, so the vocabulary carries over even though the models and the policy implications are quite different.
What to do instead
At the top of any question, underline whether the subject is a single market or the whole economy. For whole-economy questions, use the aggregate demand and aggregate supply framework and the consumer price index, and explicitly state that a change in one good's price is not inflation unless it is general and sustained.
Defining the unemployment rate as the number of unemployed people divided by the total population, or including discouraged workers and part-time workers in the labour force without saying so.
The precise denominator (the labour force, which excludes people not actively seeking work) is a definitional detail that is easy to half-remember, and candidates often substitute the population figure because it is the number they recall most readily.
What to do instead
Memorise the formula as unemployed divided by the labour force, multiplied by 100, and write the definition of the labour force (employed plus unemployed who are actively seeking work) in the same sentence. When discussing limitations, note separately that discouraged workers are excluded and underemployment is not captured, rather than folding these into the definition.
Explaining the effect of a policy by asserting a conclusion ('this will reduce unemployment') without the intervening chain of reasoning from the policy instrument to the target variable.
Candidates know the expected direction of the effect from textbook summaries and assume the marker will accept the conclusion as an explanation, so they skip the mechanism that actually earns the marks.
What to do instead
Write the transmission mechanism as a numbered chain, for example: government spending rises, aggregate demand rises, firms face higher demand, firms hire additional labour, unemployment falls. Each link must name the decision-maker and the decision they change. If any link is missing, the answer is a claim, not an explanation.
Treating fiscal policy and monetary policy as interchangeable, or attributing the setting of the cash rate to the government rather than to the central bank.
Both are called 'macroeconomic policy' and both are discussed as responses to the same problems, so the institutional division of responsibility blurs, especially when the two are used together in a stimulus package.
What to do instead
Build a two-column comparison covering the authority responsible, the instruments used, the speed of implementation, the lag before effect, and the constraints. Anchor it with the fact that the Reserve Bank of Australia sets the cash rate independently while the federal government sets the budget. State the authority explicitly whenever you mention a policy.
Evaluating a policy by listing advantages and disadvantages in two unconnected paragraphs, with no judgement about which effect dominates or under what conditions.
The command word 'evaluate' is read as 'describe both sides', and candidates fear that committing to a judgement will cost marks if the marker disagrees, so they hedge by refusing to conclude.
What to do instead
Adopt a fixed structure: state the criterion (for example, magnitude, time frame, equity, or sustainability), weigh the two sides against that criterion, then write an explicit concluding sentence beginning 'Overall, ... because ...'. The judgement is marked on the quality of the reasoning, not on which side is chosen, so commit to one.
Using stimulus material as a substitute for economic theory, so the response paraphrases the data or the extract without applying a model, concept, or mechanism to it.
Stimulus is provided to be used, and candidates believe quoting it demonstrates engagement, so they summarise it rather than interrogating it.
What to do instead
For every piece of stimulus used, write a three-part sentence: the data point with its source and units, the economic concept it illustrates, and the inference drawn from it. If a paragraph contains no concept name and no inference, delete or rewrite it. Aim for one stimulus reference per substantive point, not per sentence.
Citing statistics or economic claims with no source, no date, and no indication of whether the figure is current, or inventing plausible-sounding numbers to fill a gap.
Candidates revise themes rather than data and rely on memory for magnitudes, and the pressure to sound authoritative encourages rounding a half-remembered figure into a confident one.
What to do instead
Learn a small set of anchor figures with their source and period, and in the exam write the figure with an explicit hedge where uncertain ('around', 'in recent years', 'at the time of the source'). Never fabricate a precise number. Where no figure is available, argue from direction and magnitude in words, which is fully creditable.
Answering a question about a recent policy or event with a generic textbook response that ignores the specific circumstances, institutional setting, or timing described in the question.
Candidates prepare model answers for common policy questions and reproduce them regardless of the scenario, because the familiar structure feels safer than engaging with unfamiliar detail.
What to do instead
Before planning, extract the specifics from the question (which economy, which period, which constraint) and write them at the top of the plan. Then require that at least two sentences in the response refer explicitly to those specifics. A generic answer should be treated as a draft that has not yet answered the question.