Rank mobility index explained

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 = (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.