Me. Rev. Stat. tit. 22, § 7403

Except as otherwise provided, the department shall rebase reimbursement rates for the MaineCare program and other state-funded program reimbursement rates described in section 7402 at least every 5 years. Rebasing must be based on the most recent cost report filings available or provider cost surveys or other market data when cost reports are not available. The department may provide a mechanism for subsequent adjustments to base year costs to reflect any differences it determines are material between as-filed cost reports used in rebasing and subsequent determinations of audited, allowable costs for the same fiscal period.