immediate fertility d''ine. The requirement for reliable short-term projections and the need for longterm scenarios create ,Qeiad problems not encountered in many projection exercises. The U.S. Bureau of the Ces does make severd population projections with a 100-year horizon, but because of nearreplacement fertility and a low rate of population growth, the U.S. population is one of the least problematic for such long-term projections. More typically, projections involve a time horizon no longer than 20 to 40 years.

# APPROACHES TO PROJECTING FERTILITY

A review of approaches currently used to project national fertility levels indicates that the approaches used by international agencies appear serviceable but are not entirely transparent. More sophisticated approaches have been devised but have significant diawbacks. We review the approaches used in different population projections: in previous World Bank projections; in projections of the U.N. Population Division; in projections of the Center for Intemational Research of the U.S. Bureau of the Census; in projections of some national statistical offices; and two other general strategies of use in any projection.

Previous World Bank projections. In previous World Bank population projections (e.g., Zachariah and Vu 1988), fertility rates were projected by determining a future year (referred to as the replacement year) when fertility will reach replacement level, i.e., when the net reproduction rate (NRR) will equal 1. Estimates of the replacement year were obtained from a regression equation using as predictors family planning status (a categorical variable), projected expectation of life at birth for females in 1985-90, changes in the birth rate from 1970 to 1980, and the projected TFR for 1985-90. Th dependent variable was an initial guess of the replacement year, based on other projections, country and regional comparisons, and general information about the socioeconomic and demographic situation of each country. The predicted value from the equation was rounded to the nearest year ending in 0 or _5,_ and subjective adjustments were then made on the basis of regional consistency or country-specific information. For instance, Sub-Saharan African countries in the same region were assumed to reach replacement fertility 'at more or less the same **time'** (Zachariah and Vu 1986:xvi).

Between the current period and the replacement year, total fertility rates (TFR) for most countries were obtained by fitting a reverse geometric (accelerating) curve up to 1995-2000, and a geometric (decelerating) curve thereafter. Total fertility rates after the replacement year were assumed to stay at replacement, and therefore to vary solely in response to the mortality schedule. For SubSaharan Africa, a few countries in Asia, and all countries with fertility already below replacement, it was assumed that TFR would remain constant for one or more periods before moving toward replacement.

Several shortcomings of this methodology have been pointed out (Demeny 1985; Pressat 1986; Murray 1987). Abbreviated explanations were provided in some publications, makcing it difficult for readers to understand why some countries would reach replacement fertility earlier than others. The selection of independent variables for the regression equation appears arbitrary. No explanaton was given for choosing changes in the crude birth rate and current TFR rather than the current crude birth rate and changes in TFR. The family planning status variable was based on an arbitrary categorization of a continuous variable (percent using contraception) into three levels. And the predicted replacement years sometimes appeared unsatisfactory: for the 1988-89 Bank projections (the final run that made use of this methodology), subjective adjustments to replacement years were made for about 30 countries.

U.N. projections. The approach taken in the U.N. Population Division projections foUows several general pninciples (or basic assumptions') for above-replacement and below-replacement countries, rather than unambiguous rules.

For above-replacement countries, the assumptions are that fertility will decline with the timing 2