demographic yearbook annuaire demographique 1951

are given in footnotes. Information on special classes, wherever
available, is also given in footnotes, with an indication
as to whether the figures have or have not been included in
the major categories. Frontier traffic (the 'movement of
persons residing in the frontier areas, moving frequently
across the border and often authorized to use simplified
documents or "frontier cards"') has been excluded from
table 30 though data relating to frontier traffic for the two
countries that supplied them are shown in footnotes.
Thedata on emigrants and immigrants presented in tables
31 to 34 vary considerably around the central concept of
permanence. For example, the figures for a few countries
relate to all passengers without distinction. These figures
include persons who would not be called migrants by most
definitions. How useful an index of migration such data
constitute for a given time and country remains for the user
to determine in each case, until it has become possible to
publish more readily comparable data.
In certain countries the statistics refer to both aliens and
nationals; sometimes separate figures are given for each of
these two categories. Many countries include only nationals
or only aliens. Other limitations restrict the comparability
of the total numbers of migrants: inter-continental, or continental,
migrants only; exclusion of persons travelling by
air; exclusion of persons of certain races etc. These limitations
have been recorded in footnotes to the tables whenever
they were apparent in the source documents.
A fundamental difficulty affecting the comparability of
statistics of international migration lies in the diversity of
sources from which the data are drawn. The following are
the chief kinds of sources represented in the statistics of
emigrants and immigrants shown in tables 31 to 34: (I) port
statistics, (II) frontier control, (III) registration coupons,
(IV) transport contracts, (V) passport records and (VI)
local registers of population. The origin of the statistics is
given in the tables for each country.
Some uniformity in the methods of collection would
clearly improve the comparability of the statistics. However,
in order to obtain comparable statistics, these methods
should be equivalent rather than identical. In an island
country, port statistics may give results comparable to frontier
statistics in a country having only land borders. The
latter type of statistics may, under certain conditions, be
comparable with statistics from population registers. Only
a detailed study of each case may reveal the reliability of
the figures and how comparable they may be between countries
and times.
A common instance of variations in administrative practices
which severely limit the comparability of classifications
of migrants is in the recording of information on the country
of intended residence (or of last residence). Some countries
do not register the country of intended (or of last) permanent
residence, but merely the country of intended (or of last)
residence, which might well be a country of transit. A small
number of countries classify immigrants by country of birth
or by country of citizenship, instead of by country of last
residence. There is a correlation between these classifications;
but the degree of correlation depends on the circumstances
of place and time. It cannot be investigated except
in the very rare cases where two or more types of classifications
are given together. In view of the almost complete lack
of uniformity in the designations found in the sources, the
footnotes to tables 31 and 32 give whatever indication was
obtainable on the meaning of country of intended residence
of emigrants and of country of last residence of immigrants.
It is natural to examine also how well, for a given year,
the number of emigrants leaving a country E for a country I
coincide with the number of immigrants in country I recorded
as arriving from country E. This would require comparability
of a higher degree of perfection than has been
considered hitherto in this text. It is not surprising, therefore,
that the corresponding figures from tables 31 and 32
should differ considerably for most pairs of countries. In
itself this fact does not imply. that the data lack in reliability
and comparability to the point of being of little or no value.
On the contrary, in order that corresponding emigration
and immigration figures should be even approximately
equal for any two countries, so many difficult conditions
would have to be met that equality should not be expected,
for the time being at least. The principal of these conditions
are: equivalence in all countries of methods of collection
and of the definition of immigrant and emigrant; identity
of time references of the data; compatibility of the respective
lists of countries of intended residence and of countries of
last residence. Less fundamental conditions would also have
to be satisfied, such as recording of persons changing their
destination en route and of births and deaths during the
period of travel; adjustment of the data for differences in
the time references of the questions put to the migrants at
the places where the data are collected, so as to deal with
journeys extending beyond the end of a calendar year. However,
even where all these conditions are not fulfilled, the
data may be still useful for many purposes involving more
limited international comparability. Where apparent discrepancies
in corresponding figures are known to arise from
a failure to meet one or other of these conditions an explanatory
footnote is appended.
Tables 31 to 34 continue, up to 1950, the series appearing
in previous editions of the Yearbook. Data for 1945-1947
have been omitted this year and consequently several countries
which had been included in previous editions, but for
which more recent data cannot be presented, do not appear
in these tables. In addition, Switzerland has been omitted
from tables 32 and 34 because these data are no longer
compiled.
In tables 31 and 32, which present data for 16 areas, the
total number of emigrants (or immigrants) shown for each
country is the sum of the sub-totals by continents and of
the figure for "unknown" destinations (or origins). However,
the sub-total for a continent is not necessarily the sum
of the figures given for the countries of that continent since
it may also include figures for countries not listed individually.
In those cases where there are significant numbers
of migrants going to (or coming from) a country not listed
in the stub the details are given in a footnote.
Data on migrants by age and sex are shown in tables 33
and 34 for 14 and 13 areas respectively. For most of the
countries data are available in 5-year age groups up to 29
years and in la-year age groups from 30 to 59 years. However,
practices vary and in some cases only broad agegroups,
corresponding to children and adults, are available.
A more comprehensive compilation of migration statistics
by age and sex covering the period 1918-1947 is now in
preparation in the Social Affairs Department of the United
Nations.
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