The economics diagram that contradicts the text
Economics optional written paper, 20-mark essay: 'Evaluate the view that a maximum price on rented housing always improves affordability.' The candidate draws a supply-and-demand diagram: the vertical axis is labelled 'quantity of housing' and the horizontal axis is labelled 'price'. The price ceiling is drawn below equilibrium, and the candidate labels the resulting gap 'surplus'. In the text, the candidate correctly explains that a ceiling below equilibrium creates excess demand, mentions black markets, reduced maintenance, and misallocation, and gives examples from Berlin and Stockholm. The conclusion says the policy 'can help some tenants in the short run but may reduce supply'. The mark scheme gives 8 marks for accurate diagram and economic analysis, 8 for evaluation, and 4 for structure and communication. The candidate's analysis paragraph is strong, but the diagram is mislabelled. The examiner must decide whether the diagram error is a minor communication slip or a conceptual error, and how to award evaluation marks.
1. Diagnose the diagram: which parts are conceptual errors and which are presentation errors? How should this affect the 8 analysis marks?
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Two distinct issues. Reversing the axes is a presentation error that makes the diagram non-standard; it can confuse the reader but does not by itself prove misunderstanding. Labelling the gap a 'surplus' is a conceptual error: a ceiling below equilibrium creates excess demand, which is a shortage, not excess supply. The text correctly says excess demand, which shows the candidate knows the concept but has mislabelled the diagram. Award partial diagram credit: the ceiling position and the gap are shown, but the label and axes lose marks. For the 8 analysis marks, award most of the text-based analysis but withhold the diagram-accuracy component. Do not give full analysis marks for a contradictory diagram, and do not give zero when the text is correct.
2. How should evaluation marks be awarded given the strong examples and conclusion?
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Evaluation marks reward judgement: short run versus long run, elasticity of supply, quality effects, black markets, and counterarguments. The candidate gives examples from Berlin and Stockholm and concludes that the policy balances short-run help with supply reduction. That is genuine evaluation, so award high in the 8-mark band. It is not full marks if the essay never considers that supply may be inelastic in the short run or that affordability depends on which tenants are targeted. Examples illustrate; they do not replace analysis. A defensible award is around 6 to 7 out of 8, with the final mark depending on whether the conclusion weighs the criteria explicitly. The diagram error should not reduce evaluation marks unless it undermines the argument being evaluated.
3. What feedback would you give to prevent the candidate from losing marks on diagrams in future?
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Feedback: draw the diagram before writing the essay, label axes 'Price' vertically and 'Quantity' horizontally every time, and use a checklist: ceiling below equilibrium means shortage; floor above equilibrium means surplus. Annotate the shortage with arrows. Reconcile the diagram with the text before finishing. In the exam, spend 30 seconds checking that labels match the words 'excess demand' in the paragraph. A diagram that contradicts the text costs marks twice if the examiner is not careful, so consistency is part of communication. The candidate should also practise translating the diagram into one sentence: 'At the ceiling price, quantity demanded exceeds quantity supplied by the horizontal gap.' That sentence protects both the diagram mark and the analysis mark.