Cal. Rev. & Tax. Code § 1817
Commencing with the 1987-88 fiscal year and annually thereafter, the board shall determine the statewide and county-by-county ratio of assessed value to fair market value of locally assessed commercial and industrial real property in California. The board shall publish these ratios.
The board shall determine these ratios by sales-assessment ratio studies of commercial and industrial property which has been transferred, which may be supplemented by board appraisals and by review of the amount of new construction added to the assessment rolls each year. The board shall conduct ratio studies in accordance with statistical principles applicable to those studies.
For this purpose, the board and its duly authorized representatives shall have access to all records, public or otherwise, of any county assessor, and further, the board shall prescribe by rules the information which shall be necessary to be developed by the county assessors to enable the board to perform sales-assessment ratio studies and the format in which the data or information shall be transmitted by the county assessors to the board.
Ca. Rev. and Tax. Code § 1817