Structurally, there is substantial South-South and North-North migration; in 2013, 38% of all migrants had migrated from developing countries to other developing countries, while 23% had migrated from high-income OECD countries to other high-income countries. The United Nations Population Fund says that "while the North has experienced a higher absolute increase in the migrant stock since 2000 (32 million) compared to the South (25 million), the South recorded a higher growth rate. Between 2000 and 2013 the average annual rate of change of the migrant population in developing regions (2.3%) slightly exceeded that of the developed regions (2.1%)."