**LXXXIV INTRODUCTION**

**improvements toward** which rates of change<sup>converge when the preceding equation is applied</sup> sucoemively. A minimum attaitiable level of infant mortality<sup>of 3 per thousand was used, consistent</sup> with **the higher** life expectancies allowed, instead<sup>of the previously assumed 6 per thousand.</sup>

Selectian of life rables. Those life tables are selected<sup>from the Coale-Demeny-Guo</sup> models (Coale and Demeny 1983; Coale and Guo 1990) that<sup>provide the projected life expectancy and</sup> infant mortality rates for the first three quinquennia.<sup>First, a level of the life tables is chosen to give</sup> the desired infant mortality rate (an interpolated<sup>table is constructed if necessa.y). Mortality rates</sup> up to age 14 are taken from this life tatle. Second,<sup>another level of the life tables is chosen to give</sup> rates for ages 15 and older such that the desired level<sup>of life expectancy is obtained. Among the four</sup> Coale-Demeny-Guo families (No,rth, South, East, and<sup>West), that family is chosen which minimizes</sup> the divergence between the two chosen levels.

yond the first three quinquennia, the procedure is<sup>simpler. Life expectancy is</sup> piqojc*d to 2025-30, 2050-55, and 2100-05 as described<sup>above and used in selecting levels of the</sup> West family.

The projection program used, PROJ3L (Hill 1990),<sup>is allowed to interpolate linearly</sup> across survivorship rates for intervening periods, to<sup>facilitate a smooth transition across life table</sup> families where this is necessary.

No specific attempt is made in these projections to incorporate<sup>mortality due to infection</sup> with the human immunodeficiency virus (HIV). The<sup>1IV epidemic could have important effects on</sup> mortality in particular countries. However data are still too scant,<sup>and projection models sufficiently</sup> controversial, to allow incorporation of demographic effects<sup>into worldwide projections. Mortality</sup> from HIV infection should be considered an extraneous<sup>factor so far neglected in this work.</sup> Comparison with other mortality projections. Figures Al<sup>and A2 compare assumed</sup> trends in different projection exercises. Because judgments for<sup>individual countries differ, the current</sup> base estimates of life expectancy are slightly higher than those<sup>assumed by the U.N. An important</sup> result of the higher maxima for life expectancy is the marked<sup>divergence between the end points of</sup> last year's and the curreDt mortality projections. For less developed<sup>countries, the current path is</sup> virtually identical to that of the U.N. For more developed<sup>countries, the current trend is well above</sup> last year's: by 2020-25 life expectancy is four years<sup>above last year's estimate.</sup>

# _Projecing Fenility_

Future totzl fertility trends are specified by selecting a year<sup>when the net reproduction</sup> rate reacLes unity, i.e., when the average woman's fertility<sup>results in exactly replacing herself. (In</sup> this replacement y^ar, the net reproduction rate must equal<sup>1.) The pace at which fertility avproaches</sup> replacement level varies across stages of the fertility transition.<sup>After explaining how stages are</sup> distinguished, we discuss procedures for determiiuing total<sup>fertility trends in the pretransition stage,</sup> wben fertility is high and sustained fertility declin- has not started;<sup>the transition stage, when fertility</sup> is high tc medium and sustained fertility decline is in progress;<sup>and the late-transition and</sup> posttrAnsition stage. We then discuss what age-specific patterns<sup>of fertility were appli'd and make</sup> comparisons with other projections.

For curaent purposes, a fertility transition is assumed to have<sup>started if a cou. try has</sup> experienced a drop in total fertility )f at least 0.5 points over<sup>any five-year peiod, or if total fertility</sup> is **already** below 4-5 after a more gradual decline (Bulatao and<sup>Elwan 1985). The pretransition stage</sup> is the stage before any such decline is evident. The late-transition<sup>and posttransition stage is defined</sup> by a otal fertility rate one point above replacement level<sup>(about 3.15) or lower.</sup>