The Milliman Medical Index (MMI) measures average annual medical spending for a typical American family of four covered by an employer-sponsored preferred provider organization (PPO) program. Providing a consistent benchmark of healthcare benefit costs, the MMI annually assesses the changes in those costs over the most recent five-year period. The index looks at key components of actual medical spending and charts the changes in these components over time, including cost changes for employers and employees. In addition to national cost trends, the MMI in 2009 included results for 14 major American metropolitan areas to illustrate how widely medical costs can vary by region.