Some 700 million people worldwide, or more than all the adults of North and South America combined, think the grass is greener on the other side of the fence and want to permanently move to another country, a poll showed.

Residents of sub-Saharan African countries were the most likely to want to move abroad permanently, the polls conducted in 135 countries between 2007 and this year by Gallup showed.

On average, 38 percent of the adult population in sub-Saharan Africa, or…