[영문]It is easy to learn the average income of a resident of El Salvador or Albania. But there is no systematic source of information on the average income of a Salvadoran or Albanian. We estimate a new statistic: income per natural?the mean annual income of all people born in a given country, regardless of where those people now reside. Income per natural often differs substantially from income per resident, both in its mean and in its distribution. A large part of this difference is caused by movement across borders. Indeed, for people from a number of developing countries, departing their country of birth is one of the most important sources of poverty reduction and material advancement. If economic development is that which raises human well-being, then crossing international borders is not an alternative to economic development; it is a form of economic development