THE ECONOMICS OF IMPERFECT INFORMATION 639
sumption that individuals know their accident probabilities, while insurance companies do not (which raises more interesting issues), is given in subsection 11.1 below. Another approach to the question of robustness is the subject of the next three subsections. In them we question the behavioral assumptions and the equilibrium concepts used in Section I.
11.1 Information Assumptions
Suppose that there are two groups of customers and that not all individuals within each group have the same accident probability. The average accident probability of one group is greater than that of the other; individuals within each group know the mean accident prob- ability for members of their group, but do not know their own accident probabilities. As before, the insurance company cannot tell directly the accident probability of any particular individual, or even the group to which he belongs. For example, suppose that some persons occa- sionally drink too much, while the others almost never drink. Insur- ance firms cannot discover who drinks and who does not. Individuals know that drinking affects accident probabilities, but it affects dif- ferent people differently. Each individual does not know how it will affect him.