### X INTRODUCTION

# DATA AND METHODS

The kev el.. ,,nts in these projections are<sup>base-year (mid-1985) total population</sup> estimates and agec-sx structures, base-period (1985-90)<sup>mortality, fertility, and migration rates, and</sup> assumed trends in the rates. These elements will<sup>each be described. New data have been</sup> incorporated since the previous edition; an appendix<sup>to this Introduction indicates the sources for</sup> all base-year or base-period estimates. Revised methodology<sup>for projecting vital rates is described</sup> and some of the relatively modest effects of<sup>the revision shown.</sup>

## _Total Population_ **_and_** _,Age-Sex Composition_

Estimates of the total population In mid-1985<sup>are obtained from the most recent</sup> reliable sources. W'iere possible these are recent<sup>censuses, with appropriate adjustments for</sup> underreporting, projected to mid-1985. A number<sup>of such estimates made by the United Nations</sup> (U.N.) Population Division (in _World Population_<sup>_Prospects 1988)_have- been adopted.</sup> (Prepublication versions of the estimates were generally<sup>used.) For countries with dated or</sup> unreliable census data, other official estimates may be<sup>taken, often from the U.N.</sup><sup>_Population and_</sup> _Vital Statistics Report_ and occasionally from government<sup>publications. Other sources of estimates</sup> include Eurostat (1987) and the United States Bureau<sup>of the Census (1985; Jamison, Johnson, and</sup> Engels 1987). The specific sources of information are<sup>listed by country in the appendix.</sup> The mid-1985 population of each country is distributed<sup>by age and sex using a</sup> percentage distribution often obtained from _World_<sup>_Population Prospects 1988._These distributions</sup> were estimated by the U.N. Population Division from<sup>census data adjusted for age misreporting or</sup> using stable population analysis. For most Sub-Saharan<sup>countries, World Bank estimates of current</sup> age-sex distribution were adopted instead.

## _Mortality Level and Trend_

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

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

Infant mortality rates come about as often as life expectancies from the<sup>preliminary</sup> version of _World Population Prospects 1988._ However,<sup>a number are drawn from</sup><sup>_Populaition and_</sup>