California Code, Insurance Code - INS § 11734

(a) Every workers' compensation insurer shall adhere to a uniform experience rating plan filed with the commissioner by a rating organization designated by the commissioner and subject to his or her disapproval.

(b) The commissioner shall designate a rating organization to assist him or her in gathering, compiling, and reporting relevant statistical information, and to develop a classification system. An insurer may develop its own classification system upon which a rate may be made or adopt the classification system developed by the designated rating organization; provided, however, that any classification system developed by an insurer must be filed with the commissioner 30 days prior to its use. The commissioner shall disapprove a classification system filed by an insurer pursuant to this section if the insurer fails to demonstrate that the data thereby produced can be reported consistent with the uniform statistical plan or the classification system developed by the rating organization. Every workers' compensation insurer shall record and report its workers' compensation experience to the designated rating organization as set forth in the uniform statistical plan approved by the commissioner.

(c) The designated rating organization shall develop and file manual rules, subject to the approval of the commissioner, reasonably related to the recording and reporting of data pursuant to the uniform statistical plan, uniform experience rating plan, and any classification systems that may be in effect. Every workers' compensation insurer shall adhere to the approved manual rules and experience rating plan in writing and reporting its business. No insurer shall agree with any other insurer or with a rating organization to adhere to manual rules that are not reasonably related to the recording and reporting of data pursuant to the uniform statistical plan or classification system developed by the rating organization.

(d) The designated rating organization shall also develop and file with the commissioner a weekly premium per employee for each classification used or proposed for use by that organization. The weekly premium shall be developed by applying the proposed rate for each classification to the state average weekly wage. For the purpose of this section, “state average weekly wage” means the average weekly wage paid by employers to employees covered by unemployment insurance as reported by the United States Department of Labor for California for the 12 months ending March 31 of the calendar year preceding the year in which the injury occurred.