## XViiI INTRODUCTION

Comparisons of results are provided for selected countries in Bos and Bulatao (1989). Overall, the new procedures have slight effects on the projected future course of fertility and on projected population. However, they do delay the start of fertility transition relative to the previous procedures in countries with high mortality levels. They also tend to slow fertility decline in Africa, which under the previous procedures was faster than has generally been experienced by countries passing through the fertility transition. These changes have a lasting effect on projected population for the affected countries, which tends to be somewhat higher in the lGng run. Other smaller effects also exist. For instance, the provision that allows some countries to continue fertility decline below replacement level leads to projections of slightly lower fertility in some parts of East Asia.

# _Migration Level and Trend_

Estimates of net international migrants in the base period, by sex, were made from a review of international migration statistics published by national immigration agencies, statistical organizations, and other officiii and unofficial sources; from country population estimates and projections produced by international and regional agencies, national census and statistics offices, other government organizations, interagency task forces, and research institutions; and from discussions with experts in the subject (Arnold 1989). These estimates constitute a substantial revision of estimates used in the previous edition, and involve somewhat higher levels of net migration (Table 3).

For purposes of these estimates, individuals are counted as migrants who have resided in countries different from their previous residences for at least a year. An exception is refugees living in officially designated camps, who continue to be counted in their countries of origin regardless of period of residence. Only net estimates by quinquennium were made; immigration and emigration were not estimated separately, and single-year figures were not assessed.

Estimates of future net migrants by quinquennium up to the year 2000 were also made as part of the same examination of data and sources (Arnold 1989). These estimates are strongly affected by official policies and plans in the major receiving countries. The figures were designed to total zero in each quinquennium for the whole world. After the year 2000, the number of net migrants is assumed to approach zero linearly in each country, at the estimated rate of change in their number from the period 1990.95 to the period 1995-2000, or at a rate that would make their number zero by 2025-30, whichever rate is faster. For these later periods, a zero total for worldwide net international migration was obtained by adjusting initial estimates of net migrants in three major receiving countries-the United States, Australia, and Canada--upward or downward as necessary by a proportion constant across these countries, but vary.-g by quinquennium. These adjustments were of 1 or 2 percent for the earlier periods, negligible compared to the volume of migration assuraed for these countries, but were up to 10 percent for later periods.

The age-sex distributions of migrants are determined from alternative models based on their sex ratios. If migration is heavily male, migrants are assumed to be concentrated in the age group 15-30, with few children and elderly. If migration is more balanced between males and females, proportionally more migrants are assumed to be children and elderly (Hill n.d.).

The revised migration estimates are higher than the previous estimates, particularly for the near future. In the base period, annual total net moves (i.e., not counting any moves that are balanced by moves in the opposite direction) were 900 thourand in the previous cstimates and are 1.1 million in the revised estimates. For the following two quinquennia, the changes are larger, from 630 to 990 thousand moves and from 380 to 890 thousand moves. However, even the largcst of these figures is only 1 percent of annual world growth, or the equivalent of annual increase in a single moderate-fertility country like Turkey.