42 C.F.R. § 512.325 – Participant selection and geographic areas.

(a) Selected participants. All Medicare-certified ESRD facilities and Medicare-enrolled Managing Clinicians located in a selected geographic area are required to participate in the ETC Model.
(b) Selected Geographic Areas. CMS establishes the Selected Geographic Areas by selecting all HRRs for which at least 20 percent of the component zip codes are located in Maryland, and a random sample of 30 percent of HRRs, stratified by Census-defined regions (Northeast, South, Midwest, and West). CMS excludes all U.S. Territories from the Selected Geographic Areas.