2023 IB DP Economics 模擬試題連答案詳解

### Definition and Concepts
- **Primary Commodities:** Raw materials harvested or extracted from the land or sea (e.g., agricultural products, minerals, oil).
- **Price Elasticity of Demand (PED):** A measure of the responsiveness of the quantity demanded of a good to a change in its price. For primary commodities, PED is typically inelastic (\(PED < 1\)) because they are necessities with few close substitutes.
- **Price Elasticity of Supply (PES):** A measure of the responsiveness of the quantity supplied of a good to a change in its price. For primary commodities, PES is typically inelastic (\(PES < 1\)) due to long production timeframes (e.g., growing seasons for crops) and difficulties in storing perishable goods.

### Diagrammatic Analysis
- Draw a diagram with quantity on the horizontal axis and price on the vertical axis.
- Illustrate a steep (inelastic) demand curve (\(D\)) and a steep (inelastic) supply curve (\(S_1\)).
- Show the initial equilibrium where \(D = S_1\) at price \(P_1\) and quantity \(Q_1\).
- Shift the supply curve to the left (to \(S_2\)) to represent a negative supply shock (e.g., bad weather or crop disease).
- Show the new equilibrium where \(D = S_2\) at price \(P_2\) and quantity \(Q_2\).
- The diagram will illustrate that even a relatively small shift in supply leads to a very large change in price (from \(P_1\) to \(P_2\)) because consumers and producers cannot easily adjust their quantities demanded or supplied in the short term.

### Explanation
- Because consumers cannot easily substitute agricultural products when prices rise, they continue to buy almost the same amount, which pushes the price up significantly during a shortage.
- Because producers cannot quickly increase or decrease production due to biological and time constraints, the market cannot easily buffer these supply shocks, magnifying the price swings. Consequently, small fluctuations in supply translate into high price volatility.

**Marks 1–3**:
- The response is mainly descriptive, with a limited understanding of PED, PES, or primary commodities.
- A diagram may be missing or poorly drawn, with incorrect labels.

**Marks 4–6**:
- The response shows some understanding of the concepts of inelastic PED and PES and defines them.
- A diagram is included but may have labeling errors, or the shift in supply is not clearly explained in relation to the steepness of the curves.
- Explanation is present but lacks depth or logical connection between the inelasticities and price volatility.

**Marks 7–8**:
- The response clearly defines primary commodities, inelastic PED, and inelastic PES.
- An accurate, fully labeled diagram is provided, showing steep (inelastic) demand and supply curves and the impact of a supply shift on price.
- There is a clear explanation of why primary commodities have low elasticity and how this combination leads to large price fluctuations when supply shifts.

**Marks 9–10**:
- The response meets all criteria for 7–8 marks but is highly structured and precise.
- The economic terminology is used flawlessly.
- The diagram is fully integrated into the explanation, explicitly contrasting the large change in price with the relatively small change in quantity.

An excellent response will be structured as follows: 1. Introduction: Define key terms such as tariffs (a tax on imported goods), protectionism, and domestic employment. State the core debate: while tariffs can safeguard jobs in specific protected sectors, they impose costs on consumers, create inefficiencies, and risk retaliatory job losses in exporting sectors. 2. Diagrammatic Analysis: A fully labelled tariff diagram is essential. The diagram should show the domestic demand (Dd) and supply (Sd) curves, the world price (Pw) under free trade, and the higher tariff price (Pw + t). It must illustrate that at the world price, domestic production is Q1 and imports are Q1 to Q4. With the tariff, the domestic price rises to Pw + t, domestic production expands to Q2, and imports shrink to Q2 to Q3. The expansion from Q1 to Q2 represents increased domestic production, which directly leads to an increase in domestic employment in this protected industry. 3. Arguments Supporting Tariffs for Employment: Protecting domestic jobs in infant industries allows them to grow and achieve economies of scale. It protects workers in sunset industries from sudden structural unemployment, giving them time to adjust. It also raises government tax revenue (the area of the tariff revenue rectangle), which can be reinvested in the economy. 4. Arguments Against Tariffs and Limitations: Tariffs cause deadweight losses (welfare loss triangles) due to allocative inefficiency. Consumers face higher prices and reduced consumer surplus, which lowers their purchasing power and can reduce employment in other sectors of the economy. Additionally, domestic firms using imported inputs face higher production costs, reducing their competitiveness. Retaliation from trading partners can harm the country's export industries, leading to job losses there. 5. Alternative Policies: Subsidies to domestic producers can increase domestic production to Q2 without raising prices for consumers, though they carry an opportunity cost for the government budget. Supply-side policies, such as retraining programs, improve occupational mobility and address structural unemployment more sustainably in the long run. 6. Evaluation and Synthesis: Tariffs may provide a short-term political and economic fix to protect specific jobs. However, they are rarely the 'most effective' policy in the long run. Subsidies might be preferable as they avoid consumer welfare loss, though they require government funding. For long-term economic health, supply-side policies that facilitate structural change are far more effective than shielding inefficient industries behind trade barriers.

Level 1 (1-3 marks): The response is mainly irrelevant or lacks basic economic theory. Only a few terms are defined. Level 2 (4-6 marks): The response shows some understanding of tariffs but lacks a clear or correct diagram. The link to domestic employment is weak or unexamined. Level 3 (7-9 marks): The response includes a mostly correct tariff diagram and explains how the tariff increases domestic employment (Q1 to Q2). There is a one-sided explanation of the effects of tariffs. Level 4 (10-12 marks): The response features a fully correct and explained tariff diagram. It provides a balanced analysis of the advantages and disadvantages of tariffs on employment, and introduces at least one alternative policy (e.g., subsidies). Level 5 (13-15 marks): The response meets all Level 4 criteria and offers a well-structured, critical evaluation of whether tariffs are the 'most effective' policy, supported by strong economic reasoning and a clear comparison with alternative policies (such as subsidies or supply-side measures).