Why are externalities sometimes called spillover effects?

• A. Because the costs or benefits spill over to third parties not involved in the transaction.
• B. Because the effects are fully internalized by the market participants.
• C. Because externalities are always private goods.
• D. Because public policy has no effect on externalities.

Answer: (A)

Externalities occur when the actions of buyers or sellers affect other people who aren’t part of the transaction, creating spillover effects. That means costs or benefits flow to outsiders, not just to the parties directly involved. When these spillovers aren’t reflected in market prices, the market can’t allocate resources efficiently, which is why such effects are labeled spillovers.

That’s why the correct explanation fits best: the costs or benefits spill over to third parties not involved in the transaction. It’s not about the goods being private or public, and it’s not true that these effects are fully internalized by the market. In fact, policy tools like taxes or subsidies are often used to shift these external costs or benefits back into the price system to improve efficiency.