Rank mobility index

In demographics, the rank mobility index (RMI) is a measure of a city's change in population rank among a group of cities.^[1][2]

Formally

${\displaystyle RMI={\frac {R_{1}-R_{2}}{R_{1}+R_{2}}},}$

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.^[3][4]