of expatriate populations for the following
reasons.
• Censuses may seek to exclude persons
who are not citizens and/or permanent
residents, which will exclude some expatriates.
• In some cases, expatriates have not got full
working rights and avoid being counted in
an official census.
• Some expatriates avoid being counted in
national censuses because they perceive
that it is not relevant to them.
• The census may not be able to identify all
expatriates since it may have only a question
on birthplace, which does not necessarily
identify expatriates, or it may only
have a question on citizenship, which has
similar problems.
• It excludes second and later generations.
These notwithstanding, much can be gained
from bringing together census data of destination
countries to build up origin/destination
matrices of migration. One interesting initiative
in this area has been undertaken by the OECD
(Dumont and Lemaitre, 2005), which launched
a project in July 2003 to collect from all OECD
National Statistics Officers (NSO) data on the
stocks of foreign-born populations in order ‘to
obtain by aggregating across receiving OECD
countries, data on expatriates by country of
origin’ (Dumont and Lemaitre, 2005).
What are the options for countries of
origin of migrants who wish to collect information
on the expatriates from their own
censuses? Some nations include specific questions
on residents temporarily overseas, or
have implemented specific surveys to identify
characteristics of their nationals abroad.
However, in both cases they cannot readily
be used to estimate the size of diaspora.
Asking a sample (or total population) about
regular family members who are temporarily
away of course misses whole families who
move, and also is likely only to capture people
who are away on a temporary basis. A better
approach has been developed by the
International Union for the Scientific Study of
Population (1981) which has developed two