Originally Posted by
I-Like-To-Bike
I find it easy to believe a guesstimate of a 4X IGH figure for world wide use if "IGH" also includes bicycles with single speed (with or without coaster brake) hubs as well as hubs with multiple internal speeds.
I would definitely consider single speed a separate category--there's no internal gear, just one external.
ETA--I see @
cyccommute beat me to that point.
I would guess world-wide that single gear probably is the most common type, but they're considerably cheaper and simpler than IGH.