Often a commercial insured's liability insurance program consists of several layers. The first layer of insurance generally consists of primary insurance, which provides first dollar indemnity for judgments and settlements up to the limits of liability of the primary policy. Generally, primary insurance is subject to a deductible and obligates the insured to defend the insured against lawsuits, which is normally accomplished by assigning counsel to defend the insured. In many instances, a commercial insured may elect to self-insure. Above the primary insurance or self-insured retention, the insured may have one or more layers of excess insurance to provide coverage additional limits of indemnity protection. There are a variety of types of excess insurance, including "stand-alone" excess policies (policies that contain their own terms, conditions, and exclusions), "follow form" excess insurance (policies that follow the terms of the underlying policy except as specifically provided), and "umbrella" insurance policies (excess insurance that in some circumstances could provide coverage that is broader than the underlying insurance).[36]
At the most basic level, initial ratemaking involves looking at the frequency and severity of insured perils and the expected average payout resulting from these perils. Thereafter an insurance company will collect historical loss data, bring the loss data to present value, and compare these prior losses to the premium collected in order to assess rate adequacy.[24] Loss ratios and expense loads are also used. Rating for different risk characteristics involves at the most basic level comparing the losses with "loss relativities"—a policy with twice as many losses would therefore be charged twice as much. More complex multivariate analyses are sometimes used when multiple characteristics are involved and a univariate analysis could produce confounded results. Other statistical methods may be used in assessing the probability of future losses.
Limited risk of catastrophically large losses: Insurable losses are ideally independent and non-catastrophic, meaning that the losses do not happen all at once and individual losses are not severe enough to bankrupt the insurer; insurers may prefer to limit their exposure to a loss from a single event to some small portion of their capital base. Capital constrains insurers' ability to sell earthquake insurance as well as wind insurance in hurricane zones. In the United States, flood risk is insured by the federal government. In commercial fire insurance, it is possible to find single properties whose total exposed value is well in excess of any individual insurer's capital constraint. Such properties are generally shared among several insurers, or are insured by a single insurer who syndicates the risk into the reinsurance market.
Each of following insurers who transact business in California are domiciled in California and have their principal place of business in Los Angeles, CA: Farmers Insurance Exchange (#R 201), Fire Insurance Exchange (#1267-4), Truck Insurance Exchange (#1199-9), Mid-Century Insurance Company (#1428-2), Civic Property and Casualty Company (#4241-6), Exact Property and Casualty Company (#4240-8), Neighborhood Spirit Property and Casualty Company (#4242-4).

NerdWallet averaged rates for 40-year-old men and women for 20 ZIP codes in each state and Washington, D.C., from the largest insurers, up to 12 in each state. “Good drivers” had no moving violations on record and credit in the “good” tier as reported to each insurer. For the other two driver profiles, we changed the credit tier to “poor” or added one at-fault accident, keeping everything else the same. Sample drivers had the following coverage limits:
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