## X INTRODUCTION

# DATA AND METHODS

The key elements in these projections are base-year (mid-1985) total population estimates and age-sex structures, base-period (1985-90) mortality, fertility, and migration rates, and assumed trends in the rates. The -e elements will each be described. New data have been incorporated since the previous ecidion; an appendix to this Introduction indicates the sources for all base-year or base-period estimates. Revised methodology for projecting vital rates is described and some of the relatively modest effects of the revision shown.

# _Total Population and Age-Sex Composition_

Estimates of the total population in mid-1985 are obtained from the most recent reliable sources. Where possible these are recent censuses, with appropriate adjustments for underreporting, projected to mid-1985. A number of such estimates made by the United Nations (U.N.) Population Division (in _World Population Prospects 1988)_ have been adopted. (Prepublication versions of the estimates were generally used.) For countries with dated or. unreliable census data, other official estimates may be taken, often from the U.N. _Population and Vital Statistics Report_ and occasionally from government publications. Other sources of estimates include Eurostat (1987) and the United States Bureau of the Census (1985; Jamison, Johnson, and Engels 1987). The specific sources of information are listed by country in the appendix.

The mid-1985 population of each country is distributed by age and sex using a percentage distribution often obtained from _World Population Prospects 1988._ These distributions were estimated by the U.N. Population Division from census data adjusted for age misreporting or using stable population analysis. For most Sub-Saharan countries, World Bank estimates of current age-sex distribution were adopted instead.

# _Mortality Level and Trend_

Ihis section considers the sources of mortality data used for the base period and the manner in which future trends in rmortality are defined. Future trends are specified through projections of life expectancy by sex, projections of infant mortality, and the choice of appropriate model life tables. Each of these elements will be described. Comparisons will also be made with the previous method for projecting mortality.

Data. Base-period mortality levels in the projections are represented by life expectancies by sex and itfant mortality rates for both sexes combined. Life expectancies were obtained from a variety of sources. A preliminary version of _World Population Prospects 1988_ was a common source. Other figures are based on official or other estimates appearing in _Populadon and Vital Statistcs Report_ or government publications. A few figures are taken from the U.S. Bureau of the Census (1985; Jamison. Johnson, and Engels 1987), Eurostat (1987), and Monnier (1988). These sources often report mortality levels for periods other than 1985-90, or give indices other than life expectancies, or both. Some estimation and projection is then necessary to obtain the right index. In some cases, a mortality estimate is first made for an earlier period, and an estimate for 1985-90 obtained by applying the projection methodology being described here. Some Bank sources are also cited in the appendix: Bank sector reports; Bank assessments, involving unpublished analysis of census or survey data; dI Bank estimates, or informed judgmcnts for which no further source can be cited.

Infant mortality rates come about as often as life expectancies from the prcliminary version of _World Population Prospects 1988._ However, a number are drawn from _Population and_