IB Economics 15 Marker Structure & Examples

Scoring a 15 out of 15 on an IB Economics Paper 1 or Paper 2 question requires more than just knowing the theory. Examiners are looking for a highly specific structure. If you just brain-dump your knowledge onto the page, you will likely get stuck in the 7-9 mark band.

In this guide, we will break down the exact structure you need to score top marks in any 15-mark essay question, complete with a real-world case study example.

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The DEED Framework for 15 Markers

To guarantee you hit every point on the IB mark scheme, use the DEED framework: Define, Explain, Example, Diagram.

1. Definitions (2 marks) Always start your essay by explicitly defining the key economic terms in the question. Do not assume the examiner knows that you know it. If the question is about "Negative Externalities of Production", your very first sentence should be: *"A negative externality of production occurs when the production of a good imposes spillover costs on a third party, meaning the Marginal Social Cost (MSC) is greater than the Marginal Private Cost (MPC)."*

2. Explanation (4 marks) Next, logically explain the economic theory step-by-step. Use economic vocabulary (e.g., "incentives," "marginal," "allocation of resources"). Explain the mechanism of *why* something happens.

3. Example (4 marks) This is where most students lose marks. You must use a specific, real-world example to illustrate your theory. Do not invent a hypothetical example like "Imagine a widget factory." Instead, write: *"For example, a coal power plant in China polluting the local air represents a negative production externality."*

4. Diagram (5 marks) A 15-mark essay without a diagram will rarely score above a 9. Your diagram must be large (at least half a page), fully labeled (Price, Quantity, MSC, MPC, MPB), and—most importantly—**integrated into your text**.

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Examiner Tip: Integrate Your Diagrams Never just draw a diagram and leave it floating on the page. You must actively reference it in your explanation. For example: *"As seen in Figure 1, the free market equilibrium occurs at P1 and Q1, where MPC = MPB. However, the socially optimum output is at Q*, creating a welfare loss represented by the shaded triangle."*

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Worked Example: 15-Mark Essay Outline

Let's look at how to structure a response to a classic past paper question.

Question: *Explain how the existence of negative externalities of production results in an over-allocation of resources. (15 marks)*

Introduction

• Define: Negative externality of production, Marginal Private Cost (MPC), Marginal Social Cost (MSC), Market Failure.

• State: Because firms only consider their private costs (MPC) and ignore external costs, the free market over-produces the good.

Body Paragraph 1: The Theory & Diagram

• Draw: A negative production externality diagram showing MPC, MSC, MPB (which equals MSB), and the welfare loss triangle.

• Explain: Explain that profit-maximizing firms produce where MPC = MPB (Free market equilibrium at Q1, P1). However, society desires production where MSC = MSB (Social optimum at Q*, P*).

• Integrate: Because Q1 > Q*, there is an over-allocation of resources to this market.

[ 🖼️ INSERT EXTERNALITY DIAGRAM HERE ]

Body Paragraph 2: The Real-World Application

• Example: The coal industry in India.

• Apply: Explain how the coal factories only pay for labor and machinery (MPC) but impose massive health costs on local residents via air pollution (the external cost). Because the factory doesn't pay this health cost, their cost of production is artificially low, leading them to over-produce coal relative to what is socially desirable.

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Common Pitfalls to Avoid

• Writing a conclusion: 15-mark questions (unlike 25-mark Part B questions) do not require evaluation or a conclusion. Save your time! You only need to *explain*, not evaluate.

• Missing labels on diagrams (e.g., forgetting to label the welfare loss).

• Using generic examples instead of specific, real-world case studies.

By sticking rigidly to the DEED structure, you ensure that you are handing the examiner exactly what they are looking for on the mark scheme.