42 C.F.R. § 417.552
(a) Basic rule. The HMO or CMP must apportion its total allowable direct and indirect costs among its Medicare enrollees, its other enrollees, and its nonenrolled patients—
(b) Purpose of apportionment. The purpose of apportionment is to ensure that—
[50 FR 1346, Jan. 10, 1985, as amended at 58 FR 38082, July 15, 1993; 60 FR 46230, Sept. 6, 1995]