Data sources and methodology for
estimating the international migrant stock:
The basic data to estimate the international migrant stock were obtained
mostly from population censuses held during the decennial rounds of censuses.
Some of the data used were obtained from population registers and nationally
In the majority of cases, the sources available had gathered information on
the place of birth of the enumerated population, thus allowing for the identification
of the foreign-born population. In estimating the international migrant stock,
international migrants have been equated with the foreign-born whenever possible.
In most countries lacking data on place of birth, information on the country of
citizenship of those enumerated was available and was used as the basis for the
identification of international migrants, thus effectively equating international
migrants with foreign citizens.
Among the 230 countries or areas that constituted the world in 2008, 221,
representing 91 per cent of the total, had at least one data source on the
international migrant stock. For 179 of them (78 per cent), the data used as the
basis for estimation were the number of foreign-born persons. For another 42
(18 per cent), the number of international migrants was based on data regarding
foreign citizens. The nine countries with no information include China, the
Democratic People's Republic of Korea, Eritrea and Somalia, which have not been
major destinations for international migrants other than refugees, as well as
some small island States and city States.
Given the nature of the data available and the extent of their coverage, a
straightforward method of estimation was used. For the 195 countries having information
on the international migrant stock for at least two points in time, interpolation or
extrapolation using an exponential growth rate was used to estimate the international
migrant stock on 1 July of the reference years, namely, 1990, 1995, 2000, 2005 and
2010. In some instances, the estimates were adjusted on the basis of other relevant
information, including the size of the total population in the country, to ensure that
the proportion of migrants in small populations did not increase to unacceptable levels.
Only one source of data was available for 26 countries, including seven of the 15
successor States of the former USSR. In the case of these seven successor States,
estimates were derived by considering the number of persons enumerated by the 1989
census of the former USSR and taking into account the migration flows that have
occurred between 1990 and 2005. The trend estimated was maintained constant in
extrapolating to 2010. For all other countries with only one data source, estimates
for the reference years were derived by assuming growth rates of the migrant stock
in the years preceding or following the only data source available. For the nine
countries or areas for which no information was available on the international migrant
stock, a model, based on the general observation that the proportion of international
migrants tends to be inversely related to the size of the total population, was used.
Information by sex was available for 211 countries or areas, constituting 95 per cent
of the countries or areas with at least one source of information on the number of
international migrants. Among them, data by sex and country of birth were available
for 169 countries or areas, while data classified by sex and country of citizenship
were available for 42 countries or areas. In the 19 countries with no information by
sex, the proportion of female migrants was assumed to equal the regional average. In
the five successor States of the former USSR lacking data classified by sex, the
proportion of female migrants among all migrants was assumed to equal the average
proportion calculated from the 10 successor States having data classified by sex.
For three countries in Western Asia hosting a significant number of Palestinian
refugees, the proportion of female migrants among all migrants was assumed to equal
that derived from UNRWA data.
Source: United Nations, Department of Economic and Social Affairs, Population
Trends in International Migrant Stock: The 2008 Revision
(United Nations database, POP/DB/MIG/Stock/Rev.2008).