1957 - United Nations Statistics Division

the life table commonly described by the symbol qa;, in
which the subscript "x" refers to the age. The values
shown in Table 25 are expressed as 1,000 qa; and represent
the number dying in the year per 1,000 reaching age "x",
or the probability per 1,000 of dying within one year (or
within the specified age interval) after reaching age "x".
"Ages" in Table 25 (as well as in Tables 24 and 26) are
13 in number, i.e., 0, I, 2, 5, 10, 15, 20, 30,40, 50, 60, 65,
and 70 years.
The life-table mortality rate differs from the central
death rate in that it refers to persons reaching the given
age during the course of a year, rather than to persons of
that age in the middle of the year. Thus, the rates are
similar in concept to the infant-mortality rates shown in
Table 9. But the life-table mortality rate for persons
under 1 year of age usually differs from the type of infantmortality
rate shown in Table 9 through being adjusted
so that infant deaths are related to the cohort of births
among which they occurred.
The complete life table gives values for each single
year of age. An abridged life table gives values for
grouped ages, usually 5-year age groups. Some of the data
in Table 25 are of the latter type and are so indicated by
run-in box-heads. In these cases, the mortality rate is the
probability of dying, not within one year after reaching
the age indicated, but within 5 years of that age (or
within the specified number of years).
Coverage: Rates are shown in Table 25 for 7I geographic
areas. Lack of reliable base data restricts the number of
areas for which life tables are available but, even so, the
coverage has increased notably in the last few years.
Where national data are not available, values for subnational
areas-such as cities or provinces-are shown.
These sub-national values are presented in small type to
distinguish them from national data.
Limitations: Life-table mortality rates are subject to all the
limitations of population and registration statistics in
general. Moreover, since the aberrations due to age reporting
are usually "smoothed out" to obtain a succession
of reasonable values from age to age, comparability may
be impaired by differences in methods of adjustment.
Special problems arise in deriving qa; values for the
very young ages and for the end of life. For the young
ages, qa; values are frequently obtained by using the statistics
of births occurring in the last few years and estimating
from them the number of persons at risk of dying in
the period to which the life table relates. At the older
ages, data are frequently so scanty or unreliable that they
have to be subjected to considerable manipulation if a
reasonable series of qa; values is to be derived from them.
In many cases, the life-table qa; values at the high ages do
not depend in any way on the registered deaths at those
ages, but have been estimated on the basis of qa; figures
for younger ages.
Table 26
Life-table survival values for males and females separately
from each life table available since 1900 are presented
in Table 26.
These, commonly known as Ta; values, are derived from
the qa; of the life table; they represent the number of
males or females surviving to each successive age or
42
central age out of a cohort born alive and subjected
thereafter to the mortality rates of the given life table.
In other words, these values are the proportion of persons
born alive who are expected to survive to any given
age "x".
The radix of the life tables (the initial cohort) is usually
100,000, although in some cases shown in Table 26,
it is 10,000 or 1,000. The ages shown are 0, 1,2,5, 10, 15,
20, 30, 40, 50, 60, 65, and 70 years.
Coverage: Table 26 includes survival values for 72 geographic
areas. As noted in connexion with life-table
mortality rates (Table 25), the number of areas for which
values are available has increased since 1953 despite the
lack of reliable base data. Sub-national, i.e., city or provincial
data, are shown in Table 26 whenever national
data were not available. These figures have been set in
smaller type for easy identification.
Limitations: Like other values of the life table, these are
subject to the general limitations of the basic population
and death statistics and, in addition, to variations in the
methods used to construct the life table.
The uncertainty of mortality rates at the very young
and older ages introduces a special problem, as noted in
connexion with Table 25. Because of this, values for
older ages especially are little more than estimates.
MIGRATION STATISTICS
Table 27-31 contain statistics on international population
movements. This is the first time since 1954 that
statistics of migratory movement have been shown in the
Demographic Yearbook, and the tables have been
planned to supplement the previously published series.
Table 27 is the "master table", which sets forth the
number of international travellers by major categories
of departures and arrivals; Tables 28-31 provide statistics
on two of these categories by selected characteristics, i.e.,
permanent emigrants and immigrants by country of intended
or last residence and by age and sex. Statistics in
these 4 tables relating to permanent migrants are the
most useful for demographic research; they are, therefore,
more detailed than those on international travellers. All
five tables conform to the United Nations Recommendations
for the Improvement of International Migration
Statistics. 58
The Recommendations give equal importance to the
publication by every country of certain other tabulations
of permanent migrants, namely that by country of birth
or citizenship and, for migrants of working age, the
tabulation by usual occupation for each sex separately.
It was, however, not possible to include such tables in
this issue of the Demographic Yearbook, because the
number of countries for which adequate data were available
was too small and because of methodological difficulties.
58 The Recommendations were adopted by the Population and Statistical
Commissions of the Economic and Social Council after detailed
consultations with governments and interested international
agencies; they were endorsed by the Council in Resolution 469.E
(XV) of 27 April 1953. The text of the Recommendations is available
in Chapter II of International Migration Statistics. United Nations.
Statistical Office. Document STJSTATjSER.Mj20, September 19.'13.
(Sales No. 1953XVII.1O)