Insurance is a device for indemnifying or guaranteeing an individual against loss. Reimbursement is made from a fund to which many individuals exposed to the same risk have contributed certain specified amounts, called premiums. Payment for an individual loss, divided among many, does not fall heavily upon the actual loser. The essence of the contract of insurance, called a policy, is mutuality. The major operations of an insurance company are underwriting, the determination of which risks the insurer can take on; and rate making, the decisions regarding necessary prices for such risks. The underwriter is responsible for guarding against adverse selection, wherein there is excessive coverage of high risk candidates in proportion to the coverage of low risk candidates. In preventing adverse selection, the underwriter must consider physical, psychological, and moral hazards in relation to applicants. Physical hazards include those dangers which surround the individual or property, jeopardizing the well-being of the insured. The amount of the premium is determined by the operation of the law of averages as calculated by actuaries.