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.

Formally

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

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.