HRSA's Index of Medical Underservice (IMU) combines four measures — the ratio of primary care providers to population, the infant mortality rate, the share of the population below the federal poverty level, and the share of the population age 65 or older — into a single composite score. An area scoring 62.0 or below qualifies for MUA designation, and lower scores indicate greater underservice. Because the IMU is scored per designated area rather than per state, a simple state average only means something once you also know how many areas contributed to it: an average built from five designations is a much noisier signal than one built from a hundred, which is why this page's severity ranking is limited to states with at least five designations.

The count ranking above answers "where is MUA designation most widespread"; the severity ranking answers "where does the average designated area fall furthest below the underservice threshold." Both are legitimate lenses, and federal placement and funding decisions can use either depending on whether the goal is broad coverage or targeting the deepest need.