Principles of insurance

Commercially insurable risks typically share seven common characteristics.

1. A large number of homogeneous exposure units. The vast majority of insurance policies are provided for individual members of very large classes.
2. Definite Loss. The event that gives rise to the loss that is subject to the insured, at least in principle, take place at a known time, in a known place, and from a known cause.
3. Accidental Loss. The event that constitutes the trigger of a claim should be fortuitous, or at least outside the control of the beneficiary of the insurance.
4. Large Loss. The size of the loss must be meaningful from the perspective of the insured. Insurance premiums need to cover both the expected cost of losses, plus the cost of issuing and administering the policy, adjusting losses, and supplying the capital needed to reasonably assure that the insurer will be able to pay claims.
5. Affordable Premium. If the likelihood of an insured event is so high, or the cost of the event so large, that the resulting premium is large relative to the amount of protection offered, it is not likely that anyone will buy insurance, even if on offer. Further, as the accounting profession formally recognizes in financial accounting standards, the premium cannot be so large that there is not a reasonable chance of a significant loss to the insurer.
6. Calculable Loss. There are two elements that must be at least estimable, if not formally calculable: the probability of loss, and the attendant cost. Probability of loss is generally an empirical exercise, while cost has more to do with the ability of a reasonable person in possession of a copy of the insurance policy and a proof of loss associated with a claim presented under that policy to make a reasonably definite and objective evaluation of the amount of the loss recoverable as a result of the claim.
7. Limited risk of catastrophically large losses. The essential risk is often aggregation. If the same event can cause losses to numerous policyholders of the same insurer, the ability of that insurer to issue policies becomes constrained, not by factors surrounding the individual characteristics of a given policyholder, but by the factors surrounding the sum of all policyholders so exposed. Typically, insurers prefer to limit their exposure to a loss from a single event to some small portion of their capital base, on the order of 5 percent.