Adverse selection and moral hazard are both caused by asymmetrical information and are sometimes difficult to distinguish from one another.
- Adverse selection is the selection bias that happens before a contract happens and moral hazard is the change in behavior that happens after a contract is in place.
- Adverse selection is the difference in behavior between low-risk and high-cost individuals which causes high-cost people to self-select a way to offload their expenses on someone else like insurance. Moral hazard is when someone does too much of something because they know they can offload their expenses on someone else.
Moral hazard arises because an individual or institution does not take the full consequences and responsibilities of its actions, and therefore has a tendency to act less carefully than it otherwise would, leaving another party to hold some responsibility for the consequences of those actions. For example, a person with insurance against automobile theft may be less cautious about locking his or her car, because the negative consequences of vehicle theft are (partially) the responsibility of the insurance company.
Economists explain moral hazard as a special case of information asymmetry, a situation in which one party in a transaction has more information than another. In particular, moral hazard may occur if a party that is insulated from risk has more information about its actions and intentions than the party paying for the negative consequences of the risk. More broadly, moral hazard occurs when the party with more information about its actions or intentions has a tendency or incentive to behave inappropriately from the perspective of the party with less information.
The term adverse selection was originally used in insurance. It describes a situation where an individual’s demand for insurance (either the propensity to buy insurance, or the quantity purchased, or both) is positively correlated with the individual’s risk of loss (e.g. higher risks buy more insurance), and the insurer is unable to allow for this correlation in the price of insurance. This may be because of private information known only to the individual (information asymmetry), or because of regulations or social norms which prevent the insurer from using certain categories of known information to set prices (e.g. the insurer may be prohibited from using information such as gender or ethnic origin or genetic test results).
The potentially ‘adverse’ nature of this phenomenon can be illustrated by the link between smoking status and mortality. Non-smokers, on average, are more likely to live longer, while smokers, on average, are more likely to die younger. If insurers do not vary prices for life insurance according to smoking status, life insurance will be a better buy for smokers than for non-smokers. So smokers may be more likely to buy insurance, or may tend to buy larger amounts, than non-smokers. The average mortality of the combined policyholder group will be higher than the average mortality of the general population. From the insurer’s viewpoint, the higher mortality of the group which ‘selects’ to buy insurance is ‘adverse’. The insurer raises the price of insurance accordingly. As a consequence, non-smokers may be less likely to buy insurance (or may buy smaller amounts) than if they could buy at a lower price to reflect their lower risk. The reduction in insurance purchase by non-smokers is also ‘adverse’ from the insurer’s viewpoint, and perhaps also from a public policy viewpoint.
Furthermore, if there is a range of increasing risk categories in the population, the increase in the insurance price due to adverse selection may lead the lowest remaining risks to cancel or not renew their insurance. This leads to a further increase in price, and hence the lowest remaining risks cancel their insurance, leading to a further increase in price, and so on. Eventually this ‘adverse selection spiral’ might in theory lead to the collapse of the insurance market. In studies of health insurance, an individual mandate requiring people to either purchase plans or face a penalty is cited as a way out of the adverse selection problem by broadening the risk pool.