2024 AQA IAL Economics (9640) 模擬試題連答案詳解

First, calculate the cross elasticity of demand (XED) to determine the relationship between Good X and Good Y:
\(XED = \frac{\% \Delta Q_Y}{\% \Delta P_X} = \frac{-15\%}{+10\%} = -1.5\).
Since the XED is negative, the goods are complements.

Next, calculate the income elasticity of demand (YED) for Good Y:
\(YED = \frac{\% \Delta Q_Y}{\% \Delta \text{Income}} = \frac{+8\%}{+5\%} = +1.6\).
Since the YED is positive (and greater than 1), Good Y is a normal (and luxury) good.

Therefore, Good X and Good Y are complements, and Good Y is a normal good.

Award 1 mark for the correct answer B.
Award 0 marks for any other response.

Because arable land is a key resource used only in agricultural production, the economy's maximum capacity to produce agricultural goods falls. However, the maximum capacity to produce industrial goods is unchanged. This causes a pivotal inward shift of the PPF, pivoting from the unchanged point on the industrial goods axis.

Award 1 mark for the correct answer C.
Award 0 marks for any other response.

A negative production externality means that the cost to society of producing the good is greater than the cost to the individual firm, meaning \(MSC > MPC\). Because the free market price mechanism ignores external costs, it equates marginal private benefit (MPB) to marginal private cost (MPC) to find equilibrium. Consequently, the market overproduces the good compared to the social optimum, where \(MSB = MSC\).

Award 1 mark for the correct answer B.
Award 0 marks for any other response.

The incidence of an indirect tax falls more heavily on consumers when demand is relatively inelastic (consumers are insensitive to price changes and cannot easily switch to substitutes) and supply is relatively elastic (producers are responsive to price changes and can easily reallocate resources). Therefore, consumers bear the largest share of the tax burden when demand is price inelastic and supply is price elastic.

Award 1 mark for the correct answer C.
Award 0 marks for any other response.

Complete market failure occurs when the market mechanism fails completely to supply a good or service, resulting in a 'missing market'. This is typically the case with pure public goods because the free-rider problem prevents firms from charging a price and making a profit. In contrast, partial market failure occurs when a market exists but produces the wrong quantity or price.

Award 1 mark for the correct answer D.
Award 0 marks for any other response.

To find the four-firm concentration ratio, follow these steps:
1. Find the total size of the market by summing all sales revenue:
\(Total = 40 + 30 + 15 + 8 + 4 + 3 + 10 = 110m\).
2. Sum the market share of the four largest firms (Firms A, B, C, and D):
\(Top 4 = 40 + 30 + 15 + 8 = 93m\).
3. Calculate the percentage:
\(\frac{93}{110} \times 100 \approx 84.55\%\).
Rounding to the nearest whole percentage gives 85%.

Award 1 mark for the correct answer C.
Award 0 marks for any other response.

Adverse selection is a pre-contractual asymmetric information problem. Buyers have more information about their own health status than the insurance company. Consequently, high-risk individuals (who expect to need medical care) are far more likely to buy insurance than low-risk individuals. This drives up the average cost of claims, forcing the company to raise premiums, which may price healthy people out of the market entirely.

Award 1 mark for the correct answer C.
Award 0 marks for any other response.

External economies of scale are cost advantages that arise outside of individual firms but within the industry as a whole as the industry grows. The establishment of local university courses tailored to training software engineers increases the pool of skilled labour available locally, reducing recruitment and training costs for all local tech firms. Options A, C, and D describe internal economies of scale, which occur at the level of the individual firm.

Award 1 mark for the correct answer B.
Award 0 marks for any other response.

The percentage change in price is calculated as \(\frac{12 - 10}{10} \times 100 = +20\%\). The percentage change in quantity demanded is calculated as \(\frac{700 - 1000}{1000} \times 100 = -30\%\). The price elasticity of demand (PED) is therefore \(\frac{-30\%}{+20\%} = -1.5\). Since the absolute value of PED is greater than 1, demand is price-elastic. Consequently, a price increase leads to a decrease in total revenue (from \(10,000\) to \(8,400\)).

1 mark for correct calculation of PED (-1.5) and identifying that total revenue falls (Option A).

The market equilibrium quantity is determined where marginal private benefit equals marginal private cost: \(14 - Q = 2 + 0.5Q \implies 1.5Q = 12 \implies Q = 8\). The socially optimal quantity is determined where marginal social benefit (which equals MPB, as there are no consumption externalities) equals marginal social cost: \(14 - Q = 2 + Q \implies 2Q = 12 \implies Q = 6\).

1 mark for the correct identification of the free market quantity as 8 and the socially optimal quantity as 6 (Option A).

Because demand is price-inelastic, consumers are relatively unresponsive to price changes. When the indirect tax is imposed, the supply curve shifts vertically upwards. The price rises significantly, but quantity demanded falls only slightly. Consequently, the government raises a substantial amount of tax revenue, and consumer surplus decreases significantly because consumers bear the vast majority of the tax burden.

1 mark for identifying that government tax revenue increases and consumer surplus decreases significantly (Option A).

Scarcity is the basic economic problem that arises because people have infinite wants but resources (land, labour, capital, enterprise) are finite. This mismatch forces economic agents to make choices about how to allocate resources.

1 mark for identifying that scarcity arises because human wants are infinite but resources are finite (Option A).

Adverse selection is a consequence of asymmetric information that occurs prior to a transaction. In the health insurance market, individuals who know they are high-risk are more likely to buy insurance. Because the insurer cannot perfectly distinguish high-risk from low-risk individuals, it raises premiums. This causes low-risk individuals to opt out of the market, leaving a highly risky pool of insured individuals and potentially causing the market to collapse.

1 mark for selecting the correct example of adverse selection in health insurance (Option A).

Complete market failure occurs when the market mechanism completely fails to provide a good or service. This is characteristic of pure public goods because they are non-excludable (it is impossible to prevent non-payers from consuming them) and non-rival (one person's consumption does not reduce availability to others). This leads to the free-rider problem, meaning private firms cannot charge a price and make a profit, so the good is not provided at all by the market.

1 mark for identifying that complete market failure is most likely in pure public goods due to the free-rider problem (Option A).

Accounting profit is calculated as Total Revenue minus Explicit Costs: \(500,000 - 350,000 = 150,000\). Economic profit is calculated as Total Revenue minus both Explicit and Implicit Costs: \(500,000 - (350,000 + 150,000) = 0\). Therefore, the firm is making an accounting profit of \(150,000\) and zero economic profit (also known as normal profit).

1 mark for correctly distinguishing between accounting and economic profit and identifying the values (Option A).

Dynamic efficiency is concerned with how resources are allocated over time. It is achieved when firms use supernormal profits to invest in innovation, research and development (R&D), and new production technologies. This process shifts the long-run average cost (LRAC) curve downwards and leads to the introduction of superior products, ultimately raising consumer welfare.

Award up to 3 marks as follows: 1 mark for stating that dynamic efficiency occurs over time or in the long run. 1 mark for linking it to innovation, investment, or research and development (R&D). 1 mark for explaining that it results in lower long-run average costs (shifting the LRAC curve downwards) or improved product quality/new products.

Cross elasticity of demand (XED) is a measure of consumer responsiveness. It is calculated as: \(XED = \frac{\text{% change in quantity demanded of Good A}}{\text{% change in price of Good B}}\). If the resulting coefficient is positive, the goods are substitutes, meaning consumers switch to Good A when the price of Good B rises. If the coefficient is negative, the goods are complements, meaning consumers purchase less of Good A when the price of Good B rises.

Award up to 3 marks as follows: 1 mark for defining cross elasticity of demand (XED) as the responsiveness of demand for one good to a change in the price of another (or for providing the correct formula). 1 mark for stating that a positive XED coefficient indicates substitute goods. 1 mark for stating that a negative XED coefficient indicates complementary goods.

To calculate the cross elasticity of demand (XED) for Good Y with respect to a change in the price of Good X:

1. **Calculate the percentage change in the price of Good X (\(P_X\)):**
$$\% \Delta P_X = \frac{\text{New Price} - \text{Original Price}}{\text{Original Price}} \times 100$$
$$\% \Delta P_X = \frac{10.00 - 8.00}{8.00} \times 100 = \frac{2.00}{8.00} \times 100 = +25.0\%$$

2. **Calculate the percentage change in the quantity demanded of Good Y (\(Q_Y\)):**
$$\% \Delta Q_Y = \frac{\text{New Quantity} - \text{Original Quantity}}{\text{Original Quantity}} \times 100$$
$$\% \Delta Q_Y = \frac{1,800 - 2,500}{2,500} \times 100 = \frac{-700}{2,500} \times 100 = -28.0\%$$

3. **Calculate the XED:**
$$\text{XED} = \frac{\% \Delta Q_Y}{\% \Delta P_X}$$
$$\text{XED} = \frac{-28\%}{25\%} = -1.12$$

Award marks as follows:
- **2 marks** for the correct answer: \(-1.12\) (accept \(-1.12\) or \(-1.1\) if correctly calculated, but strictly reward \(-1.12\) as requested to two decimal places).
- **1 mark** for correct method but an arithmetic error, OR for calculating the percentage changes correctly (\(\% \Delta P_X = +25\%\) and \(\% \Delta Q_Y = -28\%\)) but failing to complete the final division correctly, OR for omitting the negative sign (giving \(1.12\)).

### Step-by-Step Calculation:

1. **Calculate the percentage change in the price of train travel:**
$$\% \Delta \text{ Price} = \frac{\text{New Price} - \text{Original Price}}{\text{Original Price}} \times 100$$
$$\% \Delta \text{ Price} = \frac{15 - 12}{12} \times 100 = \frac{3}{12} \times 100 = +25\%$$

2. **Calculate the percentage change in the quantity demanded of coach travel:**
$$\% \Delta \text{ Quantity Demanded} = \frac{\text{New Quantity} - \text{Original Quantity}}{\text{Original Quantity}} \times 100$$
$$\% \Delta \text{ Quantity Demanded} = \frac{11,000 - 8,000}{8,000} \times 100 = \frac{3,000}{8,000} \times 100 = +37.5\%$$

3. **Calculate the Cross Elasticity of Demand (XED):**
$$\text{XED} = \frac{\% \Delta \text{ Quantity Demanded of Coach Travel}}{\% \Delta \text{ Price of Train Travel}}$$
$$\text{XED} = \frac{37.5\%}{25\%} = +1.5$$

### Explanation:
- The calculated XED is **+1.5**.
- Since the value is positive ($XED > 0$), it shows that train travel and coach travel are **substitutes** for each other.
- This means that when the price of train travel increases, consumers switch away from trains and buy more coach tickets, as coach travel becomes relatively more competitive and cheaper.

### Mark Breakdown:

- **1 mark** for showing the correct workings/percentage changes (i.e., % change in price is $+25\%$ and % change in quantity demanded is $+37.5\%$).
- **1 mark** for the correct final calculation of XED ($+1.5$ or $1.5$).
- **1 mark** for identifying that the positive relationship indicates the two modes of transport are **substitute goods**.
- **1 mark** for explaining the economic relationship (e.g., as the price of train travel increases, coach travel becomes relatively cheaper, causing consumers to switch from trains to coaches).

### Diagram Description:
- **Axes**: The vertical axis is labelled 'Price / Cost / Benefit' (\(P\)) and the horizontal axis is labelled 'Quantity' (\(Q\)).
- **Curves**:
- A downward-sloping Marginal Private Benefit (\(MPB\)) curve.
- A downward-sloping Marginal Social Benefit (\(MSB\)) curve positioned to the right of (above) the \(MPB\) curve.
- An upward-sloping Marginal Private Cost curve, assumed to equal Marginal Social Cost (\(MPC = MSC\)).
- **Equilibria and Quantities**:
- Free market equilibrium is determined where \(MPB = MPC\), yielding price \(P_m\) and quantity \(Q_m\).
- Socially optimal equilibrium is determined where \(MSB = MSC\), yielding price \(P_{opt}\) and quantity \(Q_{opt}\).
- Underconsumption is represented by the distance between \(Q_m\) and \(Q_{opt}\).
- **Welfare Loss (Deadweight Loss)**: A shaded triangular area pointing to the right, bounded by the \(MSB\) curve, the \(MSC\) curve, and the vertical line at \(Q_m\).

### Written Explanation:
- **Definition**: A positive consumption externality occurs when the social benefit of consumption is greater than the private benefit (\(MSB > MPB\)). In this case, getting a vaccination provides protection to others by reducing the overall risk of transmission.
- **Market Outcome**: Self-interested consumers only account for their private benefits (\(MPB\)) when making consumption decisions, ignoring the external benefits to others. This leads them to demand quantity \(Q_m\) where \(MPB = MPC\).
- **Social Optimum vs Market Failure**: The socially optimal level of consumption is \(Q_{opt}\), where the benefit to all of society equals the cost of production (\(MSB = MSC\)). Since \(Q_m < Q_{opt}\), the market under-allocates resources to vaccinations, leading to a welfare loss (represented by the shaded triangle on the diagram) and market failure.

### Mark Breakdown:
- **Up to 3 marks** for a correctly labelled and drawn diagram:
- **1 mark**: For correctly drawing and labelling the \(MPC = MSC\) curve, the \(MPB\) curve, and the \(MSB\) curve situated to the right of \(MPB\).
- **1 mark**: For showing both the market equilibrium (\(Q_m\), \(P_m\) where \(MPB = MPC\)) and the socially optimal equilibrium (\(Q_{opt}\), \(P_{opt}\) where \(MSB = MSC\)).
- **1 mark**: For correctly shading and identifying the area of deadweight/welfare loss pointing towards the optimum equilibrium.

- **Up to 3 marks** for a clear and logical explanation of the process:
- **1 mark**: For explaining that a positive consumption externality means \(MSB > MPB\) due to third-party benefits (e.g., reduced transmission of disease).
- **1 mark**: For explaining that the free-market mechanism operates where \(MPB = MPC\), ignoring external benefits, resulting in a quantity \(Q_m\).
- **1 mark**: For explaining that this leads to underconsumption (\(Q_m < Q_{opt}\)) and an under-allocation of resources, which constitutes market failure as represented by the welfare loss.

### Diagram Description:
- **Axes**: The vertical axis is labelled Price/Cost/Benefit (\(P\)) and the horizontal axis is labelled Quantity of Home Insulation (\(Q\)).
- **Curves**:
- Marginal Private Benefit (\(MPB\)) is a downward-sloping curve.
- Marginal Social Benefit (\(MSB\)) is a downward-sloping curve positioned to the right of/above \(MPB\), representing positive consumption externalities.
- Marginal Private Cost (\(MPC\)) is assumed to be equal to Marginal Social Cost (\(MSC\)), represented as an upward-sloping curve.
- **Equilibria**:
- The free-market equilibrium is at \(Q_m\) where \(MPB = MPC\), corresponding to price \(P_m\).
- The socially optimal equilibrium is at \(Q_s\) where \(MSB = MSC\).
- The shaded triangular area of deadweight welfare loss points to the right, from \(Q_m\) towards \(Q_s\).
- **Impact of Subsidy**: A subsidy equal to the marginal external benefit shifts the private demand curve (\(MPB\)) outwards to \(MPB + \text{Subsidy}\), resulting in a new private equilibrium at the socially optimal output level \(Q_s\).

### Explanation:
1. **Market Failure**: Consumers only consider their private benefits (\(MPB\)) when purchasing insulation, ignoring the positive external benefits (such as reduced carbon emissions and lower national energy demand). In a free market, this leads to underconsumption at \(Q_m\) where \(MSB > MSC\), resulting in a deadweight welfare loss.
2. **Mechanism of the Subsidy**: By introducing a subsidy paid to consumers, the cost of purchasing insulation falls. This increases the private willingness to consume, effectively shifting the private benefit curve outwards (or shifting the cost curve down) until the private equilibrium aligns with the socially optimal quantity \(Q_s\).
3. **Result**: The market failure is corrected as the output expands from \(Q_m\) to the socially optimal level \(Q_s\), internalising the externality and eliminating the deadweight loss.

**Diagram (Up to 3 marks)**:
- **1 mark**: Correctly labelled axes (Price/Cost/Benefit and Quantity) and initial curves showing positive consumption externality (\(MSB > MPB\) and \(MPC = MSC\)).
- **1 mark**: Clearly identifying the market equilibrium (\(Q_m\)) and the social optimum (\(Q_s\)) with the resulting deadweight loss area.
- **1 mark**: Showing the effect of the subsidy (shifting \(MPB\) outwards to \(MPB + \text{Subsidy}\) or \(MPC\) downwards to \(MPC - \text{Subsidy}\)) leading to the socially optimal quantity \(Q_s\).

**Written Explanation (Up to 3 marks)**:
- **1 mark**: Explaining why a free market underconsumes home insulation (consumers ignore external benefits, leading to \(Q_m < Q_s\) and deadweight loss).
- **1 mark**: Explaining the impact of the subsidy (it reduces the private cost of insulation, incentivising consumers to increase consumption).
- **1 mark**: Explaining how the subsidy internalises the positive externality, bringing the market quantity to \(Q_s\) and maximising economic welfare.

### Diagram Description:
- **Axes**: The vertical axis is labelled Price/Cost/Benefit (\(P\)) and the horizontal axis is labelled Quantity of Home Insulation (\(Q\)).
- **Curves**:
- Marginal Private Benefit (\(MPB\)) is a downward-sloping curve.
- Marginal Social Benefit (\(MSB\)) is a downward-sloping curve positioned to the right of/above \(MPB\), representing positive consumption externalities.
- Marginal Private Cost (\(MPC\)) is assumed to be equal to Marginal Social Cost (\(MSC\)), represented as an upward-sloping curve.
- **Equilibria**:
- The free-market equilibrium is at \(Q_m\) where \(MPB = MPC\), corresponding to price \(P_m\).
- The socially optimal equilibrium is at \(Q_s\) where \(MSB = MSC\).
- The shaded triangular area of deadweight welfare loss points to the right, from \(Q_m\) towards \(Q_s\).
- **Impact of Subsidy**: A subsidy equal to the marginal external benefit shifts the private demand curve (\(MPB\)) outwards to \(MPB + \text{Subsidy}\), resulting in a new private equilibrium at the socially optimal output level \(Q_s\).

### Explanation:
1. **Market Failure**: Consumers only consider their private benefits (\(MPB\)) when purchasing insulation, ignoring the positive external benefits (such as reduced carbon emissions and lower national energy demand). In a free market, this leads to underconsumption at \(Q_m\) where \(MSB > MSC\), resulting in a deadweight welfare loss.
2. **Mechanism of the Subsidy**: By introducing a subsidy paid to consumers, the cost of purchasing insulation falls. This increases the private willingness to consume, effectively shifting the private benefit curve outwards (or shifting the cost curve down) until the private equilibrium aligns with the socially optimal quantity \(Q_s\).
3. **Result**: The market failure is corrected as the output expands from \(Q_m\) to the socially optimal level \(Q_s\), internalising the externality and eliminating the deadweight loss.

**Diagram (Up to 3 marks)**:
- **1 mark**: Correctly labelled axes (Price/Cost/Benefit and Quantity) and initial curves showing positive consumption externality (\(MSB > MPB\) and \(MPC = MSC\)).
- **1 mark**: Clearly identifying the market equilibrium (\(Q_m\)) and the social optimum (\(Q_s\)) with the resulting deadweight loss area.
- **1 mark**: Showing the effect of the subsidy (shifting \(MPB\) outwards to \(MPB + \text{Subsidy}\) or \(MPC\) downwards to \(MPC - \text{Subsidy}\)) leading to the socially optimal quantity \(Q_s\).

**Written Explanation (Up to 3 marks)**:
- **1 mark**: Explaining why a free market underconsumes home insulation (consumers ignore external benefits, leading to \(Q_m < Q_s\) and deadweight loss).
- **1 mark**: Explaining the impact of the subsidy (it reduces the private cost of insulation, incentivising consumers to increase consumption).
- **1 mark**: Explaining how the subsidy internalises the positive externality, bringing the market quantity to \(Q_s\) and maximising economic welfare.

### Diagram Description
An appropriate diagram should show:
- Y-axis: Costs, Benefits, and Price \(P\)
- X-axis: Quantity of chemical fertilisers \(Q\)
- A downward-sloping demand curve labelled \(MPB = MSB\) (Marginal Private Benefit = Marginal Social Benefit).
- An upward-sloping supply curve representing private costs, labelled \(MPC\) (Marginal Private Cost).
- An upward-sloping curve representing social costs, labelled \(MSC\) (Marginal Social Cost), which lies above and to the left of the \(MPC\) curve. The vertical distance between \(MSC\) and \(MPC\) represents the marginal external cost \(MEC\).
- The free-market equilibrium point where \(MPC = MPB\), determining the market price \(P_m\) and quantity \(Q_m\).
- The socially optimum equilibrium point where \(MSC = MSB\), determining the socially optimal price \(P_s\) and quantity \(Q_s\).
- A shaded triangular area of welfare loss (deadweight loss) pointing towards the socially optimal quantity \(Q_s\), bounded by the \(MSC\) curve, the \(MSB\) curve, and the vertical line at \(Q_m\).

### Explanation
1. **Definition of terms**: A negative externality of production occurs when the production of a good imposes external costs on third parties who are not involved in the transaction. In this case, the production of chemical fertilisers generates chemical runoff, which pollutes local water sources, harming biodiversity and increasing water purification costs for local authorities.
2. **The Private Market Outcome**: In a free market, self-interested chemical producers only consider their internal costs (such as raw materials and labour), which are represented by the \(MPC\) curve. Consumers only consider their personal utility, represented by the \(MPB\) curve. The market operates at equilibrium where \(MPC = MPB\), resulting in quantity \(Q_m\) being produced and consumed.
3. **The Socially Optimum Outcome**: Society's costs include both private costs and external costs (\(MSC = MPC + MEC\)). Because there are negative external costs, the \(MSC\) curve lies above the \(MPC\) curve. The socially optimal allocation of resources occurs where the marginal social cost equals the marginal social benefit (\(MSC = MSB\)), which corresponds to quantity \(Q_s\).
4. **Market Failure**: Because the price mechanism fails to price the external pollution costs, the market overproduces chemical fertilisers (\(Q_m > Q_s\)). For every unit produced between \(Q_s\) and \(Q_m\), the cost to society (\(MSC\)) is greater than the benefit to society (\(MSB\)). This leads to a misallocation of resources and a deadweight welfare loss to society (the shaded triangle), which constitutes market failure.

### Mark Scheme Breakdown

#### **Part 1: Diagram (Up to 3 marks)**
- **1 mark**: For correctly labelled axes (Price/Cost/Benefit and Quantity) and initial equilibrium where \(MPC = MPB\) (showing \(P_m\) and \(Q_m\)).
- **1 mark**: For drawing the \(MSC\) curve above and to the left of \(MPC\), representing the external costs of fertiliser production.
- **1 mark**: For correctly identifying the socially optimum point where \(MSC = MSB\) (showing \(P_s\) and \(Q_s\)) and shading the correct area of welfare loss (deadweight loss triangle pointing left from \(Q_m\) to \(Q_s\)).

#### **Part 2: Explanation (Up to 6 marks)**
- **1 to 2 marks**: Define key terms (negative production externalities, marginal private cost vs. marginal social cost, or market failure) and apply them to the context of chemical fertilisers (e.g., runoff, river pollution).
- **3 to 4 marks**: Explain how a free market operates where \(MPC = MPB\), ignoring external costs (\(MEC\)), which leads to a free market equilibrium at \(Q_m\).
- **5 to 6 marks**: Fully explain why this results in market failure by contrasting the market outcome with the social optimum (\(MSC = MSB\) at \(Q_s\)). Show that because \(Q_m > Q_s\), there is overproduction where \(MSC > MSB\), creating a welfare loss represented by the shaded area on the diagram, reflecting an inefficient allocation of resources.

An analytical response should address two main parts: the market failure arising from single-use plastics, and the mechanism of the indirect tax in correcting it. 1. Market Failure Analysis: Single-use plastics generate significant negative externalities in consumption (such as environmental pollution and cleanup costs borne by third parties). The marginal private benefit (MPB) of consuming single-use plastic exceeds the marginal social benefit (MSB). In a free market, consumers maximise personal utility where MPB equals MPC (Marginal Private Cost), leading to a market outcome at quantity Q1 and price P1. Because external costs are ignored, this results in overconsumption relative to the socially optimal output Q* (where MSB equals MSC, assuming MSC = MPC). This creates a deadweight welfare loss, represented by the area between the MSB and MSC curves from Q* to Q1, indicating market failure. 2. Indirect Tax Analysis: An indirect tax imposed on plastic manufacturers increases their costs of production, shifting the MPC curve upwards to MPC + Tax. If the tax is set equal to the marginal external cost at the optimum output level, the new private equilibrium (where MPC + Tax intersects MPB) will align exactly with the socially optimal output level Q*. This internalises the negative externality, raising the price to consumers, reducing the quantity demanded to Q*, and eliminating the deadweight welfare loss, thereby restoring allocative efficiency.

Level 3 (9-12 marks): Strong, focused economic analysis of how single-use plastics cause negative consumption externalities and how an indirect tax corrects this. The response uses a relevant, correctly labelled externality diagram (showing MPB, MSB, MPC, MSC, the market equilibrium, the social optimum, and the welfare loss triangle) to support the analysis. Chains of reasoning are clear, logical, and well-integrated with economic terminology. Level 2 (5-8 marks): Some appropriate economic analysis of negative externalities and indirect taxes. The response may include a diagram, but it may have minor labelling errors or lacks clear integration with the written text. Explanations of how the tax resolves the market failure may have minor logical gaps. Level 1 (1-4 marks): Basic identification of negative externalities or taxes with little development. Diagram is missing, incorrect, or unlabelled. Limited economic terminology and weak chains of reasoning.

### Introduction
Housing unaffordability occurs when housing costs rise faster than household incomes, preventing low-income households from securing decent living standards. Governments can intervene in various ways. A maximum price (price ceiling) limits the rent landlords can legally charge. While this directly reduces prices for some tenants, it can create significant market distortions. This essay will analyse the impact of a maximum rent ceiling and evaluate it against alternative policies like housing subsidies and supply-side incentives.

### Analysis of a Maximum Price
A maximum price control must be set below the market equilibrium price to be binding.

**Diagram Description:**
On a standard demand and supply diagram for rental housing, the vertical axis represents Rent (
\(P\)) and the horizontal axis represents Quantity of Rental Units (
\(Q\)).
- The market demand (
\(D\)) is downward sloping, and market supply (
\(S\)) is upward sloping, intersecting at equilibrium rent
\(P_e\) and quantity
\(Q_e\).
- When the government imposes a maximum price
\(P_{max}\) below
\(P_e\), the quantity demanded increases to
\(Q_d\) (due to lower prices attracting more consumers), while the quantity supplied falls to
\(Q_s\) (as landlords withdraw properties or convert them to other uses, e.g., short-term holiday lets or sales).
- This mismatch between
\(Q_d\) and
\(Q_s\) creates a chronic shortage of housing equal to
\(Q_d - Q_s\).

**Consequences of the Shortage:**
1. **Non-Price Rationing:** Since price can no longer allocate the scarce housing, landlords use alternative criteria to select tenants, such as income level, family status, or personal preferences, which can lead to discrimination against low-income or marginalized groups.
2. **Quality Deterioration:** With a surplus of applicants, landlords have little incentive to maintain properties, leading to unsafe living conditions.
3. **Black Markets:** Tenants might pay under-the-table 'key money' to secure apartments, undermining the policy's objective of affordability.

### Alternative Policies
1. **Housing Subsidies / Vouchers:**
Rather than restricting prices, the government can subsidise the rent of low-income households directly.
- *Analysis:* This shifts the demand curve for housing to the right, which increases the market rent. If the supply of housing is highly price inelastic (due to planning restrictions), the subsidy will mostly benefit landlords through higher rents rather than making housing more affordable.
- *Evaluation:* It is expensive for the government (high opportunity cost) and can fuel rental inflation if supply is not expanded.

2. **Supply-Side Policies (Direct Provision or Subsidising Construction):**
The government can directly build social housing or provide tax breaks/subsidies to private developers to build affordable units.
- *Analysis:* This shifts the supply curve of housing to the right. In the long run, this increases quantity from
\(Q_e\) to
\(Q_{new}\) and lowers market rents to
\(P_{new}\) naturally, without causing shortages.
- *Evaluation:* This directly addresses the root cause of the problem (lack of supply). However, it is extremely costly, faces long time lags (planning permissions, construction time), and might suffer from government failure (e.g., building in areas where there is low demand).

### Conclusion & Evaluation
Setting a maximum rent is highly popular politically and provides immediate relief to those lucky enough to retain their tenancies. However, it is rarely the most effective policy in the long term because it reduces the quantity and quality of housing available, worsening the plight of many low-income families who find themselves shut out of the market entirely.

Ultimately, a maximum rent is a short-term 'band-aid'. The most effective policy combination is a supply-side expansion (relaxing planning regulations and investing in social housing) to lower equilibrium prices naturally, paired with targeted income-related housing benefits to support the most vulnerable during the transition period.

### Marking Scheme (20 Marks Total)

#### Level 4: Strong, focused analysis and evaluation (16–20 marks)
- **Analysis:** Precise, logical chains of reasoning showing how a maximum price creates shortages and inefficiency, supported by a clear reference to a demand/supply diagram.
- **Alternatives:** Accurate economic analysis of alternative policies (e.g., subsidies, state provision, planning deregulation).
- **Evaluation:** Balanced and sustained critique of maximum prices versus alternatives, leading to a well-supported final judgement.

#### Level 3: Sound analysis and some evaluation (11–15 marks)
- **Analysis:** Good understanding of maximum prices and at least one alternative policy, though some economic links may be missing or weak.
- **Evaluation:** Attempted evaluation and comparison of policies, but lacks depth or relies on unsupported assertions.

#### Level 2: Limited analysis and descriptive points (6–10 marks)
- **Analysis:** Descriptive approach to price ceilings with limited or incorrect use of diagrams.
- **Evaluation:** Superficially weighs pros/cons of maximum prices, with little comparison to alternative policies.
- **Errors:** Significant omissions in economic reasoning.

#### Level 1: Very basic understanding (1–5 marks)
- **Analysis:** Fragmented points, minimal economic terminology, or incorrect definition of a maximum price ceiling (e.g., setting it above equilibrium).
- **Evaluation:** Missing or purely descriptive remarks without economic substance.