Table
7
Table 7
presents live-birth rates specific for age of mother, by live-birth order for as
many years as possible between 1990 and 1998.
Description of
variables: Age is defined as age at last birthday, that is, the difference
between the date of birth and the date of the occurrence of the event, expressed
in completed solar years. The age
classification used in this table is the following: under 19 years, 5-year age groups
through 40-44 years, and 45 years and over.
Live-birth
order refers to the numerical order of the live birth in relation to all
previous live-born issue of the mother, irrespective of whether pregnancies were
nuptial or extra-nuptial[1].
Except where otherwise indicated, ten categories are used to classify live-birth
order: 1 through 9 and 10 or more live births.
Rate computation:
There are two types of rates in this table. This is because many countries or
areas compile birth order data only for legitimate births. Consequently the
rates in this table in some cases will refer to total births while in others to
legitimate births only (see table 6).
The rates for
total births by birth order specific for age of mother are the number of live
births in each birth-order/age group (as shown in table 6) per
Legitimate
births rates, on the other hand, are the number of legitimate live births in
each birth-order/age group (as shown in table 6) per
Since
relatively few births occur to women below 15 or above 50 years of age, birth
rates for women under 20 years of age and 45 years of age and over are computed
on the female population, total or married, as appropriate, aged 15-19 and
45-49, respectively. Similarly, the
rate for women of “All ages” is computed by dividing all live births
irrespective of age of mother by the female population, total or married, as
appropriate, aged 15-49 years.
Births to
mothers of unknown age have been distributed proportionately on the basis of
births to mothers of known age by the Statistics Division of the United Nations
prior to computing the rates.
However, in countries or areas where 10 per cent or more of the births
were in the unknown age category, a footnote was added.
Births
for which birth order was unknown are not distributed and rates were not
computed for this category. Rates
are not computed for distributions in which 10 per cent or more of the births
are included in the unknown birth-order category.
The
populations used in computing the rates are: enumerated or estimated
distribution of females by age, and by age according to marital status. First priority was given to an
acceptable estimate for the mid point of the year to which the births referred,
second priority to census returns of the same year and third priority to an
estimate of some other point of time in the year.
Population
distributions by age, sex and marital status were last published in the
Demographic Yearbook 1997, Historical Supplement (CD-ROM).
Rates in
this table are age-specific rates similar to those in table 5 but, in addition,
they are distributed according to birth order. They are, however, not specific for
birth order, because they do not take account of the parity of the total female
population, but only of parity by age group of the mother. It would be desirable to further refine
the rates by this characteristic, but the appropriate population base (female
population, total and married, by age and number of children born alive) is
usually available only for the census year and, actually, only for a limited
number of countries or areas.
Rates
presented in this table have been limited to those for countries or areas having
at least a total of
Reliability
of data: Rates computed using data from civil registers of live births which are
reported as incomplete (less than 90 per cent completeness) or of unknown
completeness are considered unreliable and are set in italics rather than in
roman type. Table 1 and the
technical notes for that table provide more detailed information on the
completeness of live-birth registration.
For more information about the quality of vital statistics data in
general, and on the completeness of estimates in particular, see section 4.2 of
the Technical Notes.
Limitations:
Rates shown in this table are subject to all the same limitations that affect
the corresponding frequencies and are listed in the technical notes for table
6.
Because
some of the rates in this table are for total live births while others are for
legitimate live births only, the usefulness of this table for international
comparability is limited. Not only
do the frequencies used in the numerators differ, but also the populations used
in the denominators are not always comparable. For total rates, female population by
age is used while for legitimate rates married female population by age is used.
The result is that in some cases the legitimate rates are higher than the total
rates because the exclusion of illegitimate live births from the numerator of
the former rate is more than counter-balanced by exclusion of unmarried women
from the denominator of this rate.
The difference between the legitimate and total rates may be particularly
striking in the 15-19 years age group since, in many countries or areas, a
substantial proportion of women in this age group are not married.
In
addition, comparability of legitimate birth rates from this table is affected
also by the composition of the population used for the computation of the
rates. Population in consensual
unions is tabulated separately for only a relatively few areas. For these few, it is possible to
construct a population base of legally married women, that is, one consisting of
married and separated women but excluding those in consensual unions and of
unknown marital status. For most
countries or areas, however, it must be assumed (for lack of specific
information) that the consensually married population is reported and counted as
“married”. Hence, the married
female population base for the rates in this table may tend to be overstated and
the rates, therefore, lower than they should be. This point should be borne in mind in
using the rates for international comparison.
With
respect to tabulation procedures as a source of non-comparability, the effect of
including delayed registrations in the age-of-mother birth tabulations may
readily be seen in the size of the specific rates for the upper age span. High birth rates for ages 45 and over
may well represent not a measure of fertility of these ages, but the age of the
mother when the birth was registered.
The
method of distributing the unknown ages is open to some criticism because of the
fact that the age-of-mother distribution for legitimate births is known to
differ from that for illegitimate births and that the proportion of “unknown
ages” is higher among illegitimate than among legitimate births.
Coverage:
Live-birth rates specific for age of mother, by live-birth order are shown for
80 countries or areas.
Earlier
data: Live birth-rates specific for age of mother, by live-birth order have been
shown previously in issues of the Demographic Yearbook featuring natality. For information on specific years
covered, readers should consult the Index.
[1] Principles and Recommendations for a Vital Statistics System Revision 2, United Nations Publication, Sales No. E.01.XVII.10, New York, 2001.