This paper describes new procedures used to project<sup>fertility in World Bank population</sup> projections. The previous procedures were in use in the Bank<sup>for over a decade and underwent occasional</sup> modification. This comprehensive revision is based on a new review<sup>of data and provides a clear rationale</sup> for future trends. The methodology may be of use for other<sup>purposes, but its main application is to the</sup> annual update of Bank population projections for all countries<sup>or economies and regions of the world. The</sup> methodology does not depend on detailed country by country<sup>analysis of determinants of fertility; though</sup> this might yield better predictions of future fertility, it is<sup>increasingly cumbersome if one wishes to project</sup> more and more countries. An attempt to predict the future<sup>can never be a genuinely scientific exercise;</sup> OL: aim is limited to formulating heuristic rules that<sup>can be supported by past trends.</sup> Past trends are examined in the period total fertility<sup>rate (TFR) and used in the definition of</sup> future trends. Other fertility indicators (i.e., the gross<sup>reproduction rate and cohort fertility rates) have</sup> certain advantages, but TFRs tend to be available for more<sup>countries and are easily understood.</sup> For this review, countries or economies are classified on<sup>the basis of fertility level and recent</sup> trends as pre-transitional, transitional, or post-transitional.<sup>All countries are assumed to move from a</sup> pre-transitional stage of high fertility through the fertility<sup>transition to a post-transitional stage of low</sup> fertility. Trends in fertility are exami **n** i-rately mA for countries in each stage.

Focusing on the transition stage, trends are analyzed<sup>for countries or economies that</sup> experienced at least part of the fertility transition after<sup>_1955._Three data set are used: World Bank</sup> estimates of past fertility since the stari of the decline;<sup>survey, census, and registration based TFR</sup> estimates; and World Bank estimates of fertility decline in<sup>the most recent period. The three data sets</sup> produce somewhat different estimates of the rate of decline.<sup>The average, around .12 annually, is used</sup> as the medium decline pattern. Regression analysis is employed<sup>to estimate the relationship between the</sup> current rate of decline in fertility, the rate of decline<sup>in the past quinquennium, and a number of</sup> socioeconomic indicators. Slow and rapid fertility decline<sup>are defined as half and twice the medium</sup> decline rate.

Focusing on the pre- and post-transitional stages, additional<sup>analyses of fertility patterns are</sup> carried out. Pre-transitional fertility trends are found<sup>to show little pattern. The start of the transition,</sup> defined as a decline of at least _.5_ points in TFR over a quinquennium,<sup>cannot be reliably predicted but</sup> appears, from previous analyses, to be subject to a mortality<sup>threshold. Post-transitional fertility trends</sup> also show little pattem. The shift from transitional decline<sup>to the post-transitional stage involves slower</sup> fertility decline, and altemative pattems of slowing are<sup>distinguished.</sup> The results of the analysis are translated into a number of<sup>rules to be applied in projecting</sup> future total fertility rates. A comparison of the results of<sup>applying these rules with previous World Bank</sup> projections and those made by the United Nations (U.N.)<sup>Population Division is provided.</sup>

# WORLD BANK POPULATION PROJECTIONS

Annually for the past 13 years, the World Bank has<sup>produced both short- and long-term</sup> population projections for all countries or economies,<sup>areas, and regions of the world. The short-term</sup> projections are used in Bank operations as relatively reliable<sup>forecasts of future population and other</sup> demographic indicators in the next 20 years or so. The long-term<sup>projections-up to 200 years-are useful</sup> primarily as illustrations of the long-lasting effects of<sup>current high population growth ("population</sup> momentum") rather than as projections of population size<sup>for applied purposes. Methodology for carrying</sup> out the projections must provide results for each country<sup>that are consistent with current trends and feasible</sup> in the long term. For example, even if current<sup>trends do not support a rise to replacement fertility in</sup> various Western countries any time soon, fertility cannot<sup>remain at current levels for more than a few</sup> decades, because extinction of national populations is not<sup>a credible scenario. Similarly, current Sub-</sup> Saharan African fertility levels would result in exponentially<sup>increasing populations that would soon</sup> number in the billions and cannot be maintained, even<sup>if current trends and conditions do not justify</sup>