lxxvi DATA AND METHODS

# DATA **AND MEODS**

The data used in each projection include base-year (mid-1985) total population estimates and age structures by sex, and base-period (1985-90) mortality, fertility and migration rates. The data, their sources and how they are derived when insufficient information is available, will be described in this section. The sources of each country's base data can be found in Table A3.

## Data

## _Population and age-sex structure_

Estimates of the mid-1985 populations are obtained from the most recent reliable sources. When possible, these estimates are obtained from recent census totals piojected to mid-1985, after adjustments have been made for under- or over-reporting. Provisional census figures that have not been evaluated are not used. A major source of adjusted census figures is the U.N. Population Division. Other sources include the U.S. Bureau of the Census, Eurostat and, for the former Soviet countries, the U.S.S.R. census publications. When no recent census figures are available, official estimates are often adopted, frequently as reported by the U.N. Statistical Office in _Population and Vital Statistics Report._ In addition, base-year population estimates may be obtained through projections of past census results with fertility, mortality, and migration rates from vital registration or surveys.

Age-sex structures are distributions of the population by age and sex. As is the case for total population, the U.N. Population Division provides many of the age-sex structures, which generally are census age structures adjusted for age-misreporting or estimations using stable population analysis when necessary. Other sources include World Bank and official estimates from recent censuses and projections from earlier censuses.

Estimates based on a more recent census generally provide more reliable information than estimates constructed through projections from earlier censuses. However, some European countries have not had a census in decades, but maintain very accurate demographic intelligence through population- and vital registers. Most other countries lack complete regstration systems and rely on cersuses, usually taken ten years apart, often supplemented with intercensal surveys. Figure Al summarizes the currentness of census counts.

## _Mortality data_

Base-period mortality levels in the projections are indicated by life-expectancies at birth by sex and infant mortality rates for both sexes combined. Life expectancies for the quinquennia 197580, 1980-85 and 1985-90 were obtained from a variety of sources, with the U.N. Population Division being the most frequent one. Others are based on estimates published in _Population and Vra Statistics Report,_ DHS reports, statistical yearbooks, census publications, World Bank reports, Eurostat (1991), Monnier and Guibert-Lantoine (1991) and the U.S. Bureau of the Census. In cases where data are not available for the desired quinquennium, or give indices other than life expectancies, some estimation and projection is then necessary to obtain the right index Further detail about the construction of current mortality estimates may be found in Bos et aL (1992).

Infant mortality rates, like life expectancies, are taken from a variety of sources. A frequently used source is the U.N. _1990 World Population Prospects._ Other sources include surveys,