Urbanization and economic development: a bias toward large cities?

"We find that a nation's urban population percentage increases with GDP per capita; industrialization; export orientation; and possibly, foreign assistance. It decreases with the importance of agriculture. Industrialization and agricultural importance have the same implications for the concentration of urban population in cities with 100,000+ population as for the urban percentage. Greater export orientation reduces such concentration. Finally, GDP per capita, population, and export orientation reduce primacy. Political factors, such as whether a country's largest city is also its capital, affect primacy. Our results do not seem to imply that developing-country urbanization today differs fundamentally from urbanization in the past."