In demographics, the rank mobility index (RMI) is a measure of a city's change in population rank among a group of cities. Formally
R M I = R 1 − R 2 R 1 + R 2 , {\displaystyle RMI={\frac {R_{1}-R_{2}}{R_{1}+R_{2}}},}
where
R1 = city's rank at time 1 R2 = city's rank at time 2 A RMI value must be between −1 and 1. A RMI of 0 indicates no change.
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