INTRODUCTION xiii The current schedule of medium increments to life expectancy is compared with the previous schedule for high-enrolment countries, as well as with the medium schedule used by the U.N. (1989), in Figure 1. (Only female life expectancy is shown.). The three schedules are close to each other, the main difference occurring at high levels of li'e expectancy, where the U.N. permits substantially more improvement. Given the long-run nature of these projections, the current schedule cannot permit rapid improvements at high levels without either higher maxima or an abrupt slowdown in improvements at some future point.

A similar comparison is made in Figure 2 of decrements to infant mortality. Neither the previous procedures nor the U.N. procedures are based on explicit schedules for infant mortality change. To allow comparison, actual decrements were calculated from country projections and curves were fitted to represent their dependence on initial level of infant mortality. Figure 2 shows that the medium decrements are generally larger than those implicit in previous World Bank and current U.N. projections (though never by more than one per thousand), possibly reflecting recent, more rapid improvements captured by the revision in methodology.

**Table** 2 .Assumed Annual Decrements to Infant Mortality Rate (per thousand)

|Initial<br>infant<br>mortality<br>|||
|---|---|---|
|rate|Hinimun|MediumMaxinum|
|150|-0.90|-2.26<br>-4.97|
|140|-1.00|-2.51<br>-5.52|
|130|-1.08|-2.71<br>-5.92|
|120|-1.13.|-2&;<br>-6.17|
|¶10|-1.16|-2.90<br>-6.29|
|100|-1.16|-2.90<br>-6.28|
|90|-1.14|-2.85<br>-6.13|
|80|-1.10|-2.73<br>-5.85|
|70|-1.03|-2.55<br>-5.45|
|60|-0.93|-2.31<br>-4.92|
|50|-0.81|-2.01<br>-4.27|
|40|-0.67|-1.65<br>-3.49|
|3c|-0.50|-1.23<br>-2.60|
|20|-0.31|-0.76<br>-1.60|
|10|-0.09|-0.23<br>-0.48|

In addition to the new schedules, the current procedures involve some individualization of country trends.

The effects of this are more difficult to assess. Bulatao and Bos (1989) report simulations for eight countries with widely varying mortality levels, which provide some impression of tne changes. For these eight countries, the new projected trends for life expectancy generally remain close to trends projected by the previous procedures, as well as to trends projected by the U.N. The main differences are in two areas. First, for countries like Norway, the current and the previous procedures agree, but the U.N. projects faster improvements, following their schedule shown in Figure 1. Second, for countries like Ghana and Bolivia, the slowness of past improvements in life expectancy is reflected in projected levels that, after two or three decades, are as much as but no more than 4-5 percent lower than those previously projected.

Infant mortality trends differ more than life expectancies from those previously produced, because the previous procedures relied on models to give infant mortality levels. The new estimates of future infant mortality are sometimes lower and sometimes higher than the previous estimates, with no consistent pattern.

The simulations showed that the crude death rate is affected by these changes, rising or falling as much as 10 percent relative to previous estimates for specific periods. On the other hand, total population is affected much less, varying from previous estimates for future periods by 2.5 percent at most.

# _Fertility Level and Trend_

After briefly describing the sources of fertility data, this section explains how future trends in fertility are determined. It then considers how the procedures compare with previous