Table 4 presents live births by age of mother, sex and urban/rural residence 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 urban/rural classification of births is the one provided by each country or area; it is presumed to be based on the national census definitions of urban population.
Reliability of data: 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 provided more detailed information on the completeness of live‑birth registration. For more information about the quality of vital statistics data in general, and the information available on the basis of the completeness estimates in particular, see section 4.2 of the Technical Notes.
Limitations: Statistics on live births by age of mother are subject to the same qualifications as have been set forth for vital statistics in general and birth statistics in particular as discussed in section 4 of the Technical Notes.
The reliability of the data, an indication of which is described above, is an important factor in considering the limitations. In addition, some live births are tabulated by date of registration and not by date of occurrence; these have been indicated by a (+). Whenever the lag between the date of occurrence and date of registration is prolonged and, therefore, a large proportion of the live‑birth registrations are delayed, birth statistics for any given year may be seriously affected.
Another factor which limits international comparability is the practice of some countries or areas not to include in live‑birth statistics infants who were born alive but died before the registration of the birth or within the first 24 hours of life, thus underestimating the total number of live births. Statistics of this type are footnoted.
Because these statistics are classified according to age, they are subject to the limitations with respect to accuracy or age reporting. The factors influencing inaccurate reporting may be somewhat dissimilar in vital statistics (because of the differences in the method of taking a census and registering a birth) but, in general, the same errors can be observed.
The absence of frequencies in the unknown age group does not necessarily indicate completely accurate reporting and tabulation of the age item. It is often an indication that the unknowns have been eliminated by assigning ages to them before tabulation, or by proportionate distribution after tabulation.
On the other hand, large frequencies in the unknown age category may indicate that a large proportion of the births are illegitimate, the records for which tend to be incomplete in so far as characteristics of the parents are concerned.
Another limitation of age reporting may result from computing age of mother at birth of child (or at time of registration) from year of birth rather than from day, month and year of birth. Information on this factor is given in footnotes when known.
When birth statistics are tabulated by date of registration rather than by date of occurrence, the age of the mother will almost always refer to the date of registration rather than to the date of birth of the child. Hence, in those countries or areas where registration of births is delayed, possibly for years, statistics on births by age of mother should be used with caution.
In a few countries, data by age refer to confinements (deliveries) rather than to live births causing under-estimation in the event of a multiple birth. This practice leads to lack of strict comparability, both among countries or areas relying on this practice and between data shown in this table and table 6. A footnote indicates the countries in which this practice occurs.
The comparability of data by urban/rural residence is affected by the national definitions of urban and rural used in tabulating these data. It is assumed, in the absence of specific information to the contrary, that the definitions of urban and rural used in connection with the national population census were also used in the compilation of the vital statistics for each country or area. However, the possibility cannot be excluded that, for a given country or area, the same definitions of urban and rural are not used for both the vital statistics data and the population census data.
Coverage: Live births by age of mother are shown for 110 countries or areas. Cross‑classification by sex of child is shown for 95 countries or areas. Data are presented by urban/rural residence for 63 countries or areas.
Earlier data: Live births by age of mother have been shown for the latest available year in each issue of the Yearbook. For information on specific years covered, readers should consult the Index.