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. 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
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.
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.
 Principles and Recommendations for a Vital Statistics System Revision 2, United Nations Publication, Sales No. E.01.XVII.10, New York, 2001.