All rates for automobile insurance...shall be made in accordance with the following provisions:
(a) rates shall not be excessive, inadequate, or unfairly discriminatory. A rate shall not be held to be excessive unless the rate is unreasonably high for the insurance coverage provided and a reasonable degree of competition does not exist for the insurance to which the rate is applicable. A determination concerning the existence of a reasonable degree of competition with respect to subsection (1)(a) shall take into account a reasonable spectrum of relevant economic tests, including the number of insurers actively engaged in writing the insurance in question, the present availability of such insurance compared to its availability, in comparable past periods, the underwriting return of that insurance over a period of time sufficient to assure reliability in relation to the risk associated with that insurance, and the difficulty encountered by new insurers in entering the market in order to compete for the writing of that insurance.
For the purpose of section 2109(1)(a) of the code, both of the following provisions shall apply:
(a) A rate is unreasonably high for the insurance coverage provided if it is unreasonably high in relation to anticipated losses or expenses, or both, or to the uncertainty of loss for the insurance coverage provided,
(b) A determination regarding the existence of a reasonable degree of competition shall give due consideration to, at a minimum, all the following:
(i) The relevant market for the coverage or the type of insurance to which the rate applies;
(ii) The number of insurers and the number of self-insurers actively engaged in writing or providing the coverage or type of insurance in the relevant market;
(iii) The distribution of rates and market shares for such insurers in the relevant market.Market shares may be measured either by premiums or exposures;
(iv) Past and prospective trends in the availability of coverage and coverage options for insurance of that type in the relevant market;
(v) Profits attributable to insurance of that type in relation to the profitability of other types of insurance, to the uncertainty of loss for that and other types of insurance, and to the amount of capital and surplus funds available to support premium writings for that and other types of insurance;
(vi) The availability and potential for firms to enter and exit the relevant market and for financial capital and surplus funds to be allocated to, and to be removed from, the relevant market.
----Source: MCL 2109(1)(a); R 500.1503