**Policy, Researcdi, and External Affairs**

K

**Population, Health, and Nutrition**

**WPS** 500

This paper -a product of the Population, Health, and Nutriiion Division, Population and Human - Resources Department is part of a continuing effort in PRE to produce sensible and fully documented population projcctions. Copies of this paper are available free from the World Bank, 1818 H Street NW, Washington DC 20433. Please contact Vivian Altfeld, room S6-065, extension 31091 (28 pages, with figures and tables).

As part of its worldwide population projections, the Bank annually provides projections of fertility in each country. This paper reviews and updates the procedures for making fertility projections.

Bos and Bulatao classify countries as pretransitional, transitional, and post-transitional on the basis of current fertility and recent trendsand examine trends separately for each group of countries. A basic assumption underlying the analysis is that fertility will fall in all countries from high levels during the pre-transitional stage, to declining levels during the transition, and to low levels during the post-transitional stage. The start of this fertility transition process is identified in the analysis by a decline in the total fertility rate of at least 0.5 points over five years.

Focusing on the transition stage, Bos and Bulatao analyze trends for countries or economies that experienced at least part of the fertility transition after 1955. They use three data sets: World Bank estimates of fertility in the latest quinquennium; survey, census, and registrationbased fertility estimates; and World Bank estimates corresponding to the two decades immediately following initial transition. The three data sets produce somewhat different estimates of the rate of decline. The average rate of total fertility decline across all the data, 0.12 annually, is subsequently used as the medium decline pattern. Slow and rapid fertility decline are defined as half and twice the medium decline rate.

Regression analysis is used to estimate the relationship between the current rate of decline in fenility and a number of socioeconomic variables. Differences in the rate of fertility change during the transition are partly explained by socioeconomic indicators, but the addition of the previous rate of change as a predictor improves the model significantly. Models with just the previous rate of change fit almost as well as those including the socioeconomic indicators.

Focusing on the pre- and post-transitional stages, the authors carry out additional analyses of fertility patterns. Pre-transitional fertility trends show little pattern. The start of the transition cannot be reliably predicted but appears, from previous analyses, to be subject to a mortality threshold. Post-transitional fertility trends also show little pattern. The shift from transitional decline to the post-transitional stage involves slower fertility decline, and alteriative pattems of slowing are distinguished.

The results of the analysis are translated into rules for projecting future fertility rates. These rules allow future fertility trends to be defined from previous trends country by country - and incorporate changes in total fertility with projected reductions in high levels of primary sterility. To allow loig-run projections, the rules assume that all countries eventually converge to replacement fertility.

The results of applying the rules are illustrated for eight countries and compared with previots World Bank projections and projections of the United Nations Population Division.

The PRE Working Paper Series disseminates the findings of work under way in the Bank's Policy, Research, and Extemal AffairsComplex. An objective of the scries is to get these findings out quickly, even ifpresentations are less than fully polished. The findings, interpretations, and conclusions in these papers do not necessarily represent official Bank policy.

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