Michigan Compiled Laws, Chapter 500. Insurance Code of 1956 § 500.2110

Sec. 2110. (1) In developing and evaluating rates pursuant to the standards prescribed in section 2109,  1 due consideration shall be given to past and prospective loss experience within and outside this state, to catastrophe hazards, if any; to a reasonable margin for underwriting profit and contingencies; to dividends, savings, or unabsorbed premium deposits allowed or returned by insurers to their policyholders, members, or subscribers; to past and prospective expenses, both countrywide and those specially applicable to this state exclusive of assessments under this code; to assessments under this code; to underwriting practice and judgment; and to all other relevant factors within and outside this state.

(2) The systems of expense provisions included in the rates for use by any insurer or group of insurers may differ from those of other insurers or groups of insurers to reflect the requirements of the operating methods of the insurer or group with respect to any kind of insurance, or with respect to any subdivision or combination thereof for which subdivision or combination separate expense provisions are applicable.

(3) Risks may be grouped by classifications for the establishment of rates and minimum premiums. The classifications may measure differences in losses, expenses, or both.