Adverse selection is an economic concept that is based on the idea that buyers and sellers have unequal knowledge about an object being traded or about a service being offered. Adverse selection occurs when buyers and sellers have different levels of information or knowledge. This asymmetric information can result in the buyer or seller having an unfair advantage in the transaction.

In the common case of insurance, buyers may have better information than the insurer about their own risk profile. For example, those who are aware they’re more liable to health risks or who know they engage in dangerous activities may purchase more insurance coverage than those who know they’re at low risk. That's because they know they’re more likely to collect on it and the insurance company may be unaware of the extra risk associated with the policyholder. This can lead to higher costs for the insurer and can result in insurers having to raise premiums for all of the policyholders in the group.

Adverse selection can also be seen in the market for used cars. Here, buyers generally have less information about the history of the car than the seller does. Scammers may take advantage of this situation by selling cars that may have hidden defects or have not been properly maintained. This could lead to buyers paying more for a car than what it is worth. To counteract this, buyers should do thorough research to make sure they are getting a good deal on any used car they buy.

Adverse selection can have a negative impact on an economy. It can lead to higher prices, reduced competition, and a lack of consumer choice. Because of this, it’s important for buyers and sellers to be informed and aware of the possibility of asymmetrical information. Additionally, businesses, policymakers, and regulators should work together to create policies that ensure the fair and transparent exchange of goods and services. This can help to prevent unfair advantages and ensure the efficient functioning of markets.