Which of the following statements best describes the demand curve for a public good in the context of the European Union (EU)?

• A. The demand curve for a public good in the EU is identical to the demand curve for a private good.
• B. The demand curve for a public good is obtained by horizontally summing the individual member states' demand curves.
• C. The demand curve for a public good in the EU is always downward sloping due to diminishing marginal utility.
• D. The demand curve for a public good is obtained by vertically summing the individual member states' demand curves.

Answer: (D)

Verified step by step guidance

1. Understand the nature of public goods: Public goods are non-excludable and non-rivalrous, meaning one person's consumption does not reduce availability to others, and people cannot be excluded from using them.
2. Recall how demand curves for private goods are aggregated: For private goods, individual demand curves are summed horizontally because each consumer's quantity demanded at a given price adds up to total market quantity.
3. Recognize the difference in aggregation for public goods: Since public goods are consumed collectively, the total willingness to pay at each quantity is the sum of all individuals' willingness to pay, which means demand curves are summed vertically.
4. Express the vertical summation mathematically: If \(D_i(p)\) represents the willingness to pay of member state \(i\) at quantity \(q\), then the total demand \(D_{total}(q)\) is given by \(D_{total}(q) = \sum_i D_i(q)\), summing prices (willingness to pay) across all states for each quantity.
5. Conclude that the demand curve for a public good in the EU is obtained by vertically summing the individual member states' demand curves, reflecting the aggregate willingness to pay at each quantity level.