The NGI is a quantitive demographic measure of neighborhood utility, in other words usefulness. I think we should go back to calling them yuppies, and change the name of your index to yuppification index, as per the sub-heading of your entry. Don't know why these associations. End of rant. This is stupid.
Gentrification happens before the businesses move in.
The way to predict the degree of gentrification is by measuring the number and type of cars parked in the street. As gentrification increases, the number of midrange and expensive cars increases. There's a difference between yuppies and gentry. The gentry are not necessarily rich. They are moving into the very poorest neighborhoods, and converting rentals into condos.