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Insurance companies have another subtle tool. They can design policies, or “screening” mechanisms, that elicit information from their potential customers. This insight, which is applicable to all kinds of other markets, earned Joseph Stiglitz, an economist at Columbia University and a former chief economist of the World Bank, a share of the 2001 Nobel Prize. How do firms screen customers in the insurance business? They use a deductible. Customers who consider themselves likely to stay healthy will sign up for policies that have a high deductible. In exchange, they are offered cheaper premiums. Customers who privately know that they are likely to have costly bills will avoid the deductible and pay a higher premium as a result. (The same thing is true when you are shopping for car insurance and you have a sneaking suspicion that your sixteen-year-old son is an even worse driver than most sixteen-year-olds.) In short, the deductible is a tool for teasing out private information; it forces customers to sort themselves.
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