People have often commented that much of the current growth of JWs is taking place in developing countries. Social researchers studying the growth of JWs, Mormons and Seventh-Day Adventists have confirmed this observation in a recently published article:
R. T. Cragun and R. Lawson
The Secular Transition: The Worldwide Growth of Mormons, Jehovah's Witnesses, and Seventh-day Adventists
Sociology of Religion, April 9, 2010; (2010) srq022v1.
You can read the article on this page:
And extra material including tables here:
In particular this table that shows higher levels of growth for JWs in countries lower on HDI (Human Development Index) scale.
Figure 2. Influence of HDI on Jehovah's Witnesses growth.