Is international economic migration spreading?

"Are the numbers of migrants growing? Proof is hard to come by--many countries' statistics do not provide reliable data for legal migration; most countries do not have good estimates for illegal migration; quite a few have no useable data at all, especially migrant-sending countries. We make use of an alternative yardstick, which over a period of time compares the number of countries that receive foreigners who are economically active or that are these persons' countries of origin.... Our yardstick includes only countries of a minimum population size fixed in terms of a comparable population base in the years 1970 and 1990."