NOT FOR QUOTATION WITHOUT PERMISSION OF THE AUTHOR
GLOBAL PROSPECTS FOR POPULATION GROWTH AND DISTRIBUTION
Nathan Keyfitz
with the collaboration of Peer Just
May 1982 WP-82-36
Working Papers are interim reports on work of the International Institute for Applied Systems Analysis and have received only limited review. Views or opinions expressed herein do not necessarily repre- sent those of the Institute or of its National Member Organizations.
INTERNATIONAL INSTITUTE FOR APPL'IED SYSTEMS ANALYSIS A-2361 Laxenburg, Austria
ABSTRACT
A c c u r a t e estimates o f f u t u r e p o p u l a t i o n s are o u t o f r e a c h o f p r e s e n t t e c h n i q u e s ; t h e methods a c t u a l l y u s e d , however t h e y a r e d e s c r i b e d , a r e e x t r a p o l a t i o n s o f p a s t t r e n d s and c a n n o t a n t i c i p a t e t u r n i n g p o i n t s i n b i r t h s o r o t h e r components. The p r e s e n t p a p e r i s no e x c e p t i o n . I t summarizes t h e e r r o r s o f p a s t work i n t h e e x p e c t a t i o n t h a t t h e s e w i l l i n d i c a t e t h e a c c u r a c y o f
t h e f i g u r e s h e r e c o n t a i n e d . The method u s e d i n t h i s p a p e r i s t o s u p p o s e s o n e y e a r i n which e a c h c o u n t r y w i l l a t t a i n , b a r e r e p l a c e - ment ( a n a v e r a g e o f a b o u t 2.3 c h i l d r e n p e r f e r t i l e c o u p l e ) a l o n g w i t h a smooth t r a n s i t i o n t o t h a t c o n d i t i o n , and a c o n t i n u a n c e o f r e p l a c e m e n t u n t i l t h e a g e d i s t r i b u t i o n s t a b i l i z e s and t h e popu- l a t i o n becomes s t a t i o n a r y . F o r most c o u n t r i e s w e t o o k t h e t u r n o f t h e c e n t u r y as a b o u t t h e t i m e when r e p l a c e m e n t would b e
r e a c h e d . E s t i m a t e s o f p o p u l a t i o n and l a b o r f o r c e are shown by a g e and s e x a t 25 y e a r i n t e r v a l s f o r 150 c o u n t r i e s ; g r o u p i n g s a r e g i v e n by c o n t i n e n t a n d d e g r e e o f development. P r i n t o u t s are a v a i l a b l e showing much more d e t a i l t h a n w e have been a b l e t o pub- l i s h i n t h i s working p a p e r .
CONTENTS
1 . POPULATION AND I T S ANOMALIES
1 . 1 . M o r t a l i t y
1 . 2 . M o r t a l i t y i n L e s s D e v e l o p e d C o u n t r i e s 1 . 3 . F e r t i l i t y
1 . 4 . T a k i n q A c c o u n t of R u r a l a n d U r b a n 1
.
5. ~ n t e r n a t i o n a l M i g r a t i o n2 . POPULATION FORECASTS: ASSUMPTIONS AND ACCURACY
2 . 1 . C h e c k A g a i n s t O t h e r Forecasts
2 . 2 . T h e L a r g e s t C o u n t r i e s
2 . 3 . A c c u r a c y of Forecasts
2 . 4 . M e a n i n g of t h e V a r i a n t s 3 . P O L I C Y
4 . A CONTRIBUTION TO TECHNIQUE
5 . TABLES PRESENTED
REFERENCES
GLOBAL PROSPECTS FOR POPULATION GROWTH AND DISTRIBUTION
1. POPULATION AND I T S ANOMALIES
P o p u l a t i o n h a s been an i m p o r t a n t p a r t o f t h e work a t IIASA from t h e s t a r t . New and p o w e r f u l t e c h n i q u e s have been d e v e l o p e d f o r t h e a n a l y s i s o f m i g r a t i o n and o t h e r components o f p o p u l a t i o n change, and t h e y have been a p p l i e d t o t h e d a t a o f many c o u n t r i e s .
The p r e s e n t work e s t i m a t e s p r e s e n t and p r o s p e c t i v e popula- t i o n f o r a l l c o u n t r i e s o f o v e r 250,000 p o p u l a t i o n , . u s i n g a s i m p l e and uniform t e c h n i q u e o f p r o j e c t i o n , and showing r e s u l t s by a g e , s e x , and l a b o r f o r c e f o r e a c h c o u n t r y . W e i n t r o d u c e t h e numeri- c a l estimates by s t u d y of t r e n d s i n t h e components o f p o p u l a t i o n
g r o w t h - b i r t h , d e a t h , migration-and p r e c e d e t h a t by a r e v i e w o f some o f t h e s p e c i a l d i f f i c u l t i e s t h a t a s t u d e n t o f p o p u l a t i o n h a s t o f a c e , whether he w i s h e s t o f o r e c a s t t h e f u t u r e o r m e r e l y t o r e l a t e p o p u l a t i o n t c o t h e r s o c i a l v a r i a b l e s . Every s e r i o u s d i s - c u s s i o n of p o p u l a t i o n h a s t o reckon w i t h i t s m u l t i p l e f a c e t s and t h e p a r a d o x e s t o which t h e s e g i v e r i s e .
P e o p l e a r e b o t h t h e purpose of p r o d u c t i o n and i t s a g e n t s . O n e ' s view of how many p e o p l e t h e r e ought t o be depends on which of t h e s e a s p e c t s one i s l o o k i n g a t : p r o d u c t i o n o r consumption.
No s u c h ambiguity a r i s e s f o r o t h e r r e s e a r c h f i e l d s - t h e more food t h e b e t t e r ; t h e more e n e r g y t h e b e t t e r . More p e o p l e p e r m i t
greater division of labor and hence greater social product, yet the limits of the milieu come closer as population grows. One who sees the division of labor as dominant will favor a larger population while one concerned with the milieu will favor a
smaller.
Technical advance and capital have been feared because they would displace people in production, and that fear is still wide-
spread; in an extreme version machines seem like quasi-humans competing with people for a place in the world. Yet it is the countries with the most capital that have also the lowest unem- ployment and correspondingly the most conspicuous need for people.
The paradox goes further. The need for people in the capital-rich countries does not translate into large families;
in those countries the very demand for labor reduces the birth rate. This perverse result occurs because the plentiful jobs to be filled draw women into the labor force, and childbearing takes second place to careers. On the other side the countries that have the hardest time making use of their citizens are the ones producing the most children.
We tell people that economic development is a goal so impor- tant that it justifies any amount of hard work and abstention from consumption in this generation. The history of England, the United States, and the USSR show how demanding the process of development is, and how little is the immediate gratification available to those who accomplish it. Yet more than half of the work force of this generation will be dead within the next 35 years, before full development can occur. The chief beneficia- ries will be the children and grandchildren of those now working and saving. Then should not people have many children, so that at least there will be many to benefit from.the hardships that are inevitable at the initiation of development? No, for re- straint in childbearing is as important for development as re- straint in consumption. All this is hard for many of the world's poor to understand.
The transition from a human population of 1 billion on the planet to some 10 billion in a sense underlies all the other
t r a n s i t i o n s t a k i n g p l a c e between t h e 1 8 t h and t h e 2 1 s t c e n t u r y . P o p u l a t i o n growth p u t s stress on food s u p p l i e s and hence on l a n d ; it i s t h e u r g e n t r e a s o n why c a p i t a l i s a t once b a d l y needed and d i f f i c u l t t o accumulate. P o p u l a t i o n h a s much of t h e r e s p o n s i - b i l i t y f o r s h o r t a g e s o f e n e r g y and m a t e r i a l s ; i t must have some r e l a t i o n t o t h e crowding o f p u b l i c f a c i l i t i e s . I n c r e a s e d popu- l a t i o n and hence more i n t e n s i v e u s e o f l a n d n a k e s d e t e r i o r a t i o n o f t h a t l a n d and s p o r a d i c o r permanent b a r r e n n e s s more l i k e l y , a s w e l l a s more s e r i o u s when it d o e s t a k e p l a c e i n p r o p o r t i o n t o t h e number of p e o p l e whose l i v i n g depends on it.
The d i v i s i o n o f t h e p l a n e t i n t o c o u n t r i e s w i t h r a t e s of i n - c r e a s e o f 2 p e r c e n t o r more, on t h e one hand, and c o u n t r i e s w i t h v i r t u a l l y z e r o i n c r e a s e on t h e o t h e r , t e l l s u s t h a t t h e most i m - p o r t a n t datum f o r p o p u l a t i o n a n a l y s i s and f o r e c a s t i n g i s t h e movement o f c o u n t r i e s from t h e one c a t e g o r y t o t h e o t h e r . When p e o p l e a r e poor a s m a l l i n c r e a s e i n income i s l i k e l y t o b e t u r n e d i n t o c h i l d r e n , t h r o u g h more b a b i e s s u r v i v i n g ; when t h e y a r e w e l l on t h e p a t h o f development a s m a l l i n c r e a s e o f income i s l i k e l y t o b e t u r n e d i n t o a f a l l o f t h e b i r t h r a t e . A t some p o i n t i n t h e i n c r e a s e o f income a f l i p o c c u r s , and what was a p o s i t i v e e f f e c t o f income on p o p u l a t i o n becomes a n e g a t i v e one.
I f two v a r i a b l e s , income and number o f c h i l d r e n , a r e p o s i - t i v e l y c o r r e l a t e d up t o a c e r t a i n t i m e , when t h e y r e a c h a thresh-, o l d , and t h e n beyond t h i s t h r e s h o l d - s t a r t t o b e n e g a t i v e l y c o r r e - l a t e d , f o r e c a s t i n g i s e s p e c i a l l y d i f f i c u l t . W e d o n o t know q u i t e how o r when a c o u n t r y rises above t h e l e v e l o f p o v e r t y where
p o p u l a t i o n grows r a p i d l y and c a s i t a l v e r y l i t t l e , t o t h e a f f l u e n t c o n d i t i o n i n which p o p u l a t i o n i s udder c o n t r o l and c a p i t a l accu- m u l a t e s r a p i d l y . Such e v e n t s a s t h e d i s c o v e r y of some new n a t u r a l r e s o u r c e , o r t h e a d v e n t o f a n e n e r g e t i c l e a d e r , p e r h a p s a d o p t i o n of a r e l i g i o n o f a b s t i n e n c e and h a r d work l i k e P u r i t a n i s m , c a n t r i g g e r t h e a d v e n t o f development, and make p r e v i o u s f o r e c a s t s of p o p u l a t i o n w o r t h l e s s . The e s t i m a t e s o f t h i s p a p e r , l i k e a l l o t h e r s , a r e i n e v i t a b l y s u b j e c t t o s u c h a r i s k .
W e proceed t o r e v i e w b r i e f l y c u r r e n t t r e n d s i n m o r t a l i t y , f e r t i l i t y , and m i g r a t i o n , r e c o g n i z i n g t h a t t h e l i t e r a t u r e on t h e c a u s e s o f m o r t a l i t y and o n f e r t i l i t y d e c l i n e and of t h e n u m e r i c a l
t e n d e n c i e s t o d a t e i s t o o r i c h t o be c a p t u r e d i n t h e s e few pages.
We p r e s e n t o u r b e s t e s t i m a t e , and compare t h a t w i t h o t h e r e s t i - mates, f o r each c o u n t r y of o v e r 250,000 p o p u l a t i o n , t h e n d i s c u s s t h e p r o b a b l e e r r o r of such e s t i m a t e s . P o p u l a t i o n p o l i c i e s and t h e i r e f f e c t i v e n e s s c a n n o t be d i s r e g a r d e d by t h e f o r e c a s t e r , and we mention them b r i e f l y f o r a few c o u n t r i e s .
1.1. M o r t a l i t y
The demographic t r a n s i t i o n i s i n i t i a t e d by t h e f a l l i n t h e d e a t h r a t e , a f a l l whose c a u s e s a r e n o t y e t d i s e n t a n g l e d . Medi- c a l advance h a s s t e a d i l y cumulated from t h e f i r s t i n t r o d u c t i o n of v a c c i n a t i o n , b u t t h e f a l l i n t h e d e a t h r a t e d o e s n o t seem t o have w a i t e d f o r t h a t . The ending o f t h e p l a g u e s t h a t were s o l a r g e a f a c t o r i n European m o r t a l i t y from t h e 1 4 t h t o t h e 1 7 t h c e n t u r y had l i t t l e t o do w i t h t h e advance o f medical knowledge, b u t was due r a t h e r t o an e c o l o g i c a l change i n which one k i n d of r a t drove o u t a n o t h e r from human s e t t l e m e n t s . I n r e c e n t y e a r s medicine h a s p l a y e d i t s p a r t , a l o n g w i t h e a r l i e r f a c t o r s o f i m - proved s a n i t a t i o n and improved d i e t . N u t r i t i o n seems t o have been i m p o r t a n t , n o t s o much because p e o p l e d i e d i r e c t l y of s t a r - v a t i o n , b u t because t h e y a r e weakened by l a c k of a n a d e q u a t e and v a r i e d d i e t and t h e r e f o r e s u s c e p t i b l e t o d i s e a s e .
The n e t r e s u l t o f a l l t h e changes h a s been a r a p i d l y s p r e a d - i n g improvement i n m o r t a l i t y c o n d i t i o n s . E x p e c t a t i o n o f l i f e a t a g e z e r o i s a s good a measure a s any of t h e p r o g r e s s t h a t h a s been made and e x p e c t e d . I n p r i m i t i v e p o p u l a t i o n s t h a t e x p e c t a t i o n i s on t h e o r d e r o f 25 o r 30 y e a r s ; Sweden, w i t h m o r t a l i t y s t a t i s t i c s a v a i l a b l e a s e a r l y a s t h e 1 8 t h c e n t u r y , showed l e s s t h a n 35 y e a r s i n i t s f i r s t l i f e t a b l e s . For t h e world a s a whole t h e e x p e c t a - t i o n h a s r i s e n by 1950-1955 t o 4 7 y e a r s , t h e n r a p i d l y i n c r e a s e d t o 58 y e a r s by 1975-1980 ( U n i t e d N a t i o n s 1981).
Among t h e many forms o f s o c i a l i n e q u a l i t y i s i n e q u a l i t y be- f o r e d e a t h . United N a t i o n s f i g u r e s show f o r 1975-1980 a n e x p e c t a - t i o n of l i f e a t b i r t h of 55 y e a r s f o r t h e l e s s developed r e g i o n s , a g a i n s t 7 2 f o r t h e more developed r e g i o n s (United N a t i o n s 1981:
8 2 ) . Within c o u n t r i e s t h e d i f f e r e n t i a l s by s e x a r e g r e a t - i n t h e developed r e g i o n s males s t a n d a t a b o u t 68 y e a r s , females
c l o s e t o 76 y e a r s , a d i f f e r e n c e of 8 y e a r s t h a t c o n t r a s t s w i t h 2 y e a r s f o r t h e LDCs. The d i f f e r e n c e f o r developed c o u n t r i e s i s a b o u t e q u a l t o t h e d i f f e r e n t i a l between smokers and non-
smokers, and s l i g h t l y g r e a t e r t h a n t h a t between b l a c k s and Whites i n t h e United S t a t e s . Though m o r t a l i t y by income w i t h i n coun- t r i e s i s h a r d e r t o measure t h a n s e x and a g e d i f f e r e n c e s , we know something a b o u t i t ( s e e , f o r example, Hauser and Kitagawa 1973, Sauvy 1957). We a l s o know t h a t some a t l e a s t of t h e r e c e n t i m - provements i n t h e United S t a t e s a r e due t o b e h a v i o r a l changes, e x e r c i s e and q u i t t i n g smoking b e i n g t h e two most i m p o r t a n t , and t h e s e may w e l l be c o r r e l a t e d w i t h s o c i a l c l a s s .
1.2. M o r t a l i t y i n Less Developed C o u n t r i e s
M o r t a l i t y improvement o v e r t h e postwar p e r i o d h a s been e s p e c i a l l y g r e a t i n t h e l e s s developed c o u n t r i e s . A s a rough measure, t h e mean l e n g t h of l i f e h a s gone up on a v e r a g e of a b o u t one-half y e a r p e r y e a r [13 y e a r s i n 25, a c c o r d i n g t o UN (1981:
82) e s t i m a t e s ] a g a i n s t a r i s e i n t h e United S t a t e s s i n c e t h e be- g i n n i n g of t h e c e n t u r y a v e r a g i n g o n l y a b o u t o n e - t h i r d of a y e a r p e r y e a r , and s i n c e 1950 o n l y a b o u t 4 y e a r s i n 25. C h i n a ' s r e c o r d i s o u t s t a n d i n g , t o judge from o f f i c i a l f i g u r e s r e p o r t e d by t h e United Nations. For t h e 25 y e a r s from 1950 t o 1975 t h e e x p e c t a t i o n of l i f e r o s e from 47 t o 68, a g a i n o f 21 y e a r s , o r
.8 o f a y e a r p e r y e a r . T h i s and o t h e r i n s t a n c e s o f r a p i d i n - c r e a s e i n mean l e n g t h o f l i f e a r e due l e s s t o t h e i n t r o d u c t i o n o f advanced m e d i c a l t e c h n i q u e s t h a n t o e x t e n s i o n o f rudimentary h e a l t h measures t o s o c i a l groups t h a t had p r e v i o u s l y been a l - t o g e t h e r w i t h o u t medical c a r e , and most p a r t i c u l a r l y t o improved d i e t and s a n i t a t i o n .
Can m o r t a l i t y r a t e s i n t h e d e v e l o p i n g world c o n t i n u e t o i m - p r o v e a t t h e pace o f t h e l a s t 30 y e a r s ? A t o n e - h a l f y e a r i n c r e a s e
i n e x p e c t a t i o n of l i f e a t age z e r o f o r e a c h c a l e n d a r y e a r t h e d e v e l o p i n g c o u n t r i e s would t a k e o n l y t h r e e decades t o p a s s t h e p o i n t where t h e advanced c o u n t r i e s now s t a n d . D e s i r a b l e a s such an advance would be, t h e r e i s r e a s o n t o d o u b t t h a t it c a n happen.
I n f a c t t h e r e h a s been a g e n t l e f a l l i n t h e g a i n s o v e r r e - c e n t decades ( s e e ~ w a t k i n 1980:615): t h e l e s s developed c o u n t r i e s
a s a whole i n c r e a s e d i n e x p e c t a n c y by . 6 4 o f a y e a r p e r y e a r d u r i n g t h e 1950s, by .60 i n t h e 1950s, by .52 i n t h e 1960s, and by o n l y .40 i n t h e 1970s. One s h o u l d n o t e x a g g e r a t e t h e a c c u r - acy o f t h e s e f i g u r e s , f o r t h e r e a r e l a r g e p a r t s o f t h e world f o r which w e d o n o t know t h e d e a t h r a t e s , b u t t h e d e c e l e r a t i o n seems
t o b e a f a c t . One c a n see t h i s s t r i k i n g l y i n i n d i v i d u a l coun- t r i e s . Egypt showed phenomenal g a i n s , up t o .9 o f a y e a r p e r y e a r , d u r i n g t h e 20 y e a r s from a b o u t 1940 t o 1960, f o l l o w e d by much s l o w e r g a i n s s i n c e . Most o f A f r i c a h a s shown g a i n s r a t h e r
less t h a n .5 o f a y e a r p e r y e a r , w i t h s l o w i n g i n r e c e n t y e a r s ; i n p a r t s o f C e n t r a l A f r i c a i t h a s even been s a i d t h a t t h e r e h a s been a n a b s o l u t e d e t e r i o r a t i o n . Y e t w e c a n n o t b e s u r e o f t h e s e a s s e r t i o n s ; t h e A f r i c a n d a t a a r e p a r t i c u l a r l y u n c e r t a i n .
Samuel P r e s t o n h a s used e c o n o m e t r i c methods t o a s c e r t a i n what p r o p o r t i o n o f t h e g a i n s i n m o r t a l i t y have b e e n d u e t o h e a l t h measures, a s a g a i n s t economic development. H e f i n d s t h a t t h e c r e d i t i s a b o u t e q u a l l y d i v i d e d , w i t h h e a l t h measures i n v o l v i n g no i n c r e a s e o f income r e s p o n s i b l e f o r a b o u t h a l f o f t h e g a i n s . The l i s t o f such measures h a s m a l a r i a c o n t r o l a t i t s h e a d , and i n c l u d e s t h e p r o v i s i o n of p r o t e c t e d w a t e r s u p p l i e s . For example, m a l a r i a c o n t r o l i s c r e d i t e d w i t h a b o u t o n e - q u a r t e r o f t h e i m - provement i n S r i Lankan l o n g e v i t y . The problems t h a t remain a r e d i a r r h e a , pneumonia, and m a l n u t r i t i o n , and t h e s e c a n n o t e a s i l y b e t a c k l e d w i t h r a i s i n g l i v i n g s t a n d a r d s . An a c c e l e r a - t i o n i n t h e development p r o c e s s c o u l d r e v e r s e t h e downtrend i n t h e r a t e o f improvement,but i t would b e o v e r - o p t i m i s t i c t o an- t i c i p a t e s u c h a c c e l e r a t i o n .
The method used f o r t h i s p a p e r d o e s n o t p r o j e c t a c t u a l mor- t a l i t y d a t a , b u t r a t h e r moves a l o n g t h e sequence of C o a l e and Demeny (1966) Model West t a b l e s . T h a t t h e s e t a b l e s a r e a good f i t t o p a s t s e q u e n c e s o f m o r t a l i t y improvement i n most p a r t s o f t h e world h a s been e s t a b l i s h e d , though Noreen Goldman (1980) f i n d s one e x c e p t i o n .
1.3. F e r t i l i t y
Many less d e v e l o p e d c o u n t r i e s r e p o r t s u c c e s s i n t h e s p r e a d o f b i r t h c o n t r o l . C e r t a i n s m a l l c o u n t r i e s around t h e r i m o f
A s i a were t h e f i r s t t o b r i n g t h e i r b i r t h r a t e s c l o s e t o t h o s e of t h e advanced c o u n t r i e s , and S i n g a p o r e i s now w e l l below re- placement. Some s o c i a l g r o u p s t h r o u g h o u t A s i a and L a t i n America have lowered t h e i r b i r t h s , and t h e s p r e a d of b i r t h c o n t r o l h a s been w i d e l y r e p o r t e d i n I n d o n e s i a and e l s e w h e r e . Y e t t h e cen- s u s e s o f 1 9 8 0 have been d i s a p p o i n t i n g , showing f o r I n d o n e s i a , f o r i n s t a n c e , a p o p u l a t i o n a b o u t 5 m i l l i o n g r e a t e r t h a n t h a t a n t i c i p a t e d on t h e b a s i s of t h e r e p o r t s o f f a m i l y p l a n n i n g ac- c e p t a n c e s . China h a s promulgated a p o l i c y of one- and t w o - c h i l d f a m i l i e s , and i f i t s p e o p l e w i l l go w i t h t h i s p o l i c y it w i l l v e r y soon f a l l below r e p l a c e m e n t . I n f a c t t h e f i g u r e of some
1 7 m i l l i o n b i r t h s f o r 1 9 7 8 c o r r e s p o n d s t o l e s s t h a n 2 1/2 c h i l d - r e n p e r f e r t i l e m a r r i e d c o u p l e , and s o i s j u s t s l i g h t l y above r e p l a c e m e n t . A t t h e o t h e r extreme of f a m i l y p l a n n i n g s u c c e s s i s A f r i c a , where b i r t h s show l i t t l e s i g n o f f a l l i n g t o conform w i t h t h e d r o p of t h e d e a t h r a t e .
U r b a n i z a t i o n h a s a complex r e l a t i o n t o f e r t i l i t y . I n
Europe and America d u r i n g t h e demographic t r a n s i t i o n c i t i e s w e r e i n t h e van, w i t h b i r t h r a t e s a t e a c h s t a g e lower t h a n r u r a l
b i r t h r a t e s . T h i s i s l e s s t r u e of t h e p r e s e n t LDCs, many o f whose c i t y p e o p l e r e t a i n t h e i r r u r a l c u l t u r e . Y e t t h e m i g r a t i o n c o n t r i b u t e s a n i n d i r e c t e f f e c t t h a t i s i m p o r t a n t i n t h e l o n g r u n . I f coming t o t h e c i t y d o e s n o t always o r immediately change p e r - s o n a l i t i e s , t h e c o n d i t i o n s o f t h e c i t y a r e s u c h t h a t u r b a n resi- d e n t s e x e r c i s e p o l i t i c a l c l a i m s f a r beyond any t h a t p e a s a n t s c a n e x e r t . Food and s h e l t e r a r e produced s p o n t a n e o u s l y i n t h e coun- t r y s i d e , w i t h o u t any a d m i n i s t r a t i v e o v e r s i g h t o r c o n t r i b u t i o n ; i n t h e c i t y t h o s e c i t i z e n s who c a n n o t produce t h e i r own c a n c a l l on government. Governments a r e alarmed by t h e expanding c i t i e s ,
f o r whose w e l f a r e t h e y a r e a s k e d t o t a k e r e s p o n s i b i l i t y . Popu- l a t i o n growth i n a p e a s a n t c o u n t r y s i d e i s i n a s e n s e h i d d e n - i t i s known t o t h e c e n s u s t a k e r s , b u t d o e s n o t have immediate and p r e s s i n g p u b l i c c o n s e q u e n c e s . The burden o f i n c r e a s e d popula- t i o n f a l l s on f a m i l i e s i n t h e form of l e s s p l e n t i f u l f o o d , a d e c l i n e i n d r a f t a n i m a l s , and s m a l l e r and s m a l l e r p l o t s o f l a n d .
I t d o e s n o t p l a c e a s d i r e c t a r e s p o n s i b i l i t y on government a s d o e s t h e e x p a n s i o n o f u r b a n p o p u l a t i o n s .
I n c o u n t r i e s t h a t have l a r g e amounts o f empty l a n d , l e a d e r s have o f t e n c a l l e d o n t h e i r p e o p l e t o s e t t l e t h e f r o n t i e r . But s u c h c o u n t r i e s a l s o h a v e h i g h r a t e s o f u r b a n i z a t i o n ; t h e popula- t i o n i n c r e m e n t i s more d i s p o s e d t o come t o t h e c i t i e s , a n d
e s p e c i a l l y t o t h e l a r g e s t c i t i e s , t h a n t o heed n a t i o n a l i s t i c ap- p e a l s . T h e r e w a s much t a l k o f f i l l i n g empty l a n d s by a m b i t i o u s governments i n t h e 1960s; by t h e 1970s t h e c o n t i n u e d f l o w t o t h e c i t i e s , f o r i n s t a n c e i n Mexico, w a s a m a j o r f a c t o r i n t u r n i n g t h e t h o u g h t s o f governments i n t h e d i r e c t i o n o f f a m i l y p l a n n i n g .
How d o s u c h c o n s i d e r a t i o n s t r a n s l a t e i n t o numbers e x p e c t e d i n t h e f u t u r e ? F o r most o f t h e c o u n t r i e s o f A s i a a n d
at in
America t h e y t e l l u s t h a t t h e d r o p o f c h i l d b e a r i n g t o r e p l a c e - ment, s a y 2.3 c h i l d r e n p e r f e r t i l e m a r r i e d c o u p l e on t h e a v e r a g e , w i l l come b e f o r e t h e t u r n o f t h e c e n t u r y ; f o r A f r i c a i t w i l l a p p a r e n t l y b e l a t e r t h a n t h a t . However, w e do n o t e s t i m a t e r e - p l a c e m e n t much l a t e r , f o r A f r i c a s t a n d s u n d e r t h e d a n g e r o f
d i s e a s e and h u n g e r , a s t h e c u r r e n t news r e p o r t s t e l l u s c o n s t a n t - l y , and it i s i n r e a l d a n g e r o f a r i s e i n i t s d e a t h r a t e . Our judgement i s t h a t r e p l a c e m e n t w i l l b e a t t a i n e d i n most o f t h e l e s s d e v e l o p e d c o u n t r i e s by 2000-2005 a t t h e l a t e s t , and by 10 y e a r s a f t e r t h a t i n A f r i c a .
1.4. T a k i n g Account o f R u r a l and Urban
The t e c h n i q u e s u s e d i n t h i s s e t o f p r o j e c t i o n s d o n o t de- compose n a t i o n a l p o p u l a t i o n s i n t o s u b g r o u p s beyond a g e and s e x . Y e t w e know t h a t i n f a c t subgroups e v o l v e d i f f e r e n t l y , and w e a l s o know t h a t w h a t e v e r t h e t e c h n i q u e o f p r o j e c t i o n , when i t i s a p p l i e d s e p a r a t e l y t o s u b g r o u p s and t h e r e s u l t s added i t comes o u t d i f f e r e n t from t h e s i m p l e p r o j e c t i o n o f t h e u n d i v i d e d whole.
I t c a n b e shown m a t h e m a t i c a l l y t h a t if s u b g r o u p s are pro- j e c t e d s e p a r a t e l y o n g e o m e t r i c i n c r e a s e , a n d t h e r e s u l t s added, t h a t a d d i t i v e t o t a l w i l l b e g r e a t e r t h a n t h e s i m p l e t o t a l ob- t a i n e d by p r o j e c t i n g t h e whole a t a r a t e o f i n c r e a s e e q u a l t o t h e w e i g h t e d a v e r a g e o f t h e i n i t i a l r a t e s o f i n c r e a s e o f t h e s u b g r o u p s ( K e y f i t z 1977:14-18). The r e a s o n i s t h a t t h o s e of t h e s u b g r o u p s t h a t a r e i n c r e a s i n g f a s t e r w i l l come t o h a v e more
w e i g h t i n t h e a d d i t i v e v e r s i o n a s t i m e goes a l o n g , w h i l e i n t h e s i m p l e v e r s i o n t h e y i m p l i c i t l y r e t a i n t h e i r i n i t i a l weight.
But t h i s g e n e r a l e f f e c t , which f o r s h o r t - t i m e i n t e r v a l s and moderate d i f f e r e n t i a l r a t e o f i n c r e a s e i s s m a l l , i s overwhelmed by a q u i t e d i f f e r e n t e f f e c t i n t h e c a s e o f a decomposition i n t o r u r a l and urban p a r t s . I n most p l a c e s and t i m e s t h e urban b i r t h r a t e i s lower t h a n t h e r u r a l , and i f o n e a l l o w s f o r t h e s h i f t of p o p u l a t i o n from r u r a l t o urban, a s i t i s t a k i n g p l a c e i n t h e l e s s developed c o u n t r i e s of t h e world t o d a y , t h e p r o j e c t i o n t o f u t u r e t i m e s would on t h i s a c c o u n t come o u t lower. Work i s now underway a t I I A S A t o improve t h e c a l c u l a t i o n by a m u l t i r e g i o n a l approach w i t h i n e a c h c o u n t r y .
1.5. I n t e r n a t i o n a l M i g r a t i o n
With t h e f i l l i n g up of t h e Americas b e f o r e t h e middle o f t h e t w e n t i e t h c e n t u r y t h e l a s t g r e a t movement a c r o s s t h e A t l a n t i c from Europe was o v e r , a n d l a r g e s c a l e i n t e r n a t i o n a l m i g r a t i o n seemed t o be a t h i n g of t h e p a s t . That proved n o t t o be so. Refugees from Cuba and Vietnam t o t h e United S t a t e s , g u e s t workers from s o u t h e r n Europe and w e s t e r n A s i a t o n o r t h e r n Europe, who s e t t l e d down a s r e s i d e n t s , l e g a l and i l l e g a l , movement from Bangladesh t o n o r t h e r n I n d i a , and a c r o s s t h e US-Mexico b o r d e r , movement from e x - c o l o n i e s t o e x - m e t r o p o l i s e s , f l i g h t from d r o u g h t and war i n A f r i c a - t h e s e a r e some o f t h e m i g r a t i o n c u r r e n t s s i n c e World War 11, w i t h a t o t a l volume unprecedented i n world h i s t o r y .
The s i x m i l l i o n g u e s t workers i n n o r t h e r n Europe, t h e r e f u - g e e s and i l l e g a l s i n t h e United S t a t e s , c a n s t i l l be t h o u g h t of a s a c o n t i n u a t i o n o f t h e s t r e a m of m i g r a t i o n t h a t b r o u g h t some 60 m i l l i o n workers t o t h e New World d u r i n g t h e c e n t u r y o r s o p r i o r t o World War 11. T h a t t r a d i t i o n a l s t r e a m c o n s i s t e d of Europeans of lower l e v e l s o f e d u c a t i o n , w i t h minimum p r o p e r t y , s k i l l , o r o t h e r a t t r i b u t e t h a t c o u l d g i v e them a s a t i s f a c t o r y p l a c e i n t h e European economy. They were welcomed t o t h e New World a s t h e y h e l p e d p u t i t s r i c h l a n d s t o p r o f i t a b l e use and c o n s t i t u t e d t h e l a b o r f o r c e o f i t s i n c i p i e n t i n d u s t r y . During t h e 65 y e a r s from t h e C i v i l War t o 1930,they brought t h e w e s t e r n p l a i n s of North America under c u l t i v a t i o n , l a b o r e d i n c l o t h i n g f a c t o r i e s i n New
York, w h i l e o t h e r b r a n c h e s o f t h e same s t r e a m o f m i g r a n t s con- t r i b u t e d t o t h e p r o d u c t i o n o f meat and wheat on t h e A r g e n t i n e pampas, and b u i l t p l a n t a t i o n s i n t h e f o r e s t s o f B r a z i l .
The m i g r a t i o n o f t h e p o s t w a r p e r i o d , and presumably t h a t o f t h e 50 y e a r s a h e a d o f u s , i s a r e s p o n s e , less warmly welcomed by t h e c i t i z e n s o f t h e r e c e i v i n g c o u n t r i e s , t o t h e i n c r e a s e d d i f f e r - e n c e s o f income between t h e p o o r and t h e r i c h c o u n t r i e s . Migra- t i o n h a s a l w a y s been up t h e income g r a d i e n t , b u t p a s t g r a d i e n t s w e r e less s t e e p , t h e p r e s s u r e t o move less i n t e n s e , and hence t h e f l o w c o u l d b e more r e a d i l y c o n t r o l l e d by t h e r e c e i v i n g coun- t r i e s . Now r e f u g e e s a p p e a r who a r e n o t e a s i l y t u r n e d down;
f o r e i g n e r s i n S w i t z e r l a n d become numerous enough t o d i s t u r b i t s c u l t u r a l homogeneity; P a k i s t a n i s and J a m a i c a n s , t h e h e r i t a g e o f a d i s s o l v e d e m p i r e , a r e i n v o l v e d i n r a c e r i o t s i n England. Refu- g e e s from c u r r e n t w a r s and from p o l i t i c a l h o s t i l i t y a r e p a r t i c u - l a r l y numerous i n A f r i c a , b u t f a r from unknown i n A s i a and L a t i n America.
Counting i l l e g a l s , i m m i g r a t i o n i n t o t h e U n i t e d S t a t e s i s t h o u g h t t o b e l a r g e r t h a n t h e m i l l i o n p l u s who e n t e r e d i n 1913, t h e h i g h e s t y e a r i n t h e o f f i c i a l r e c o r d . No o n e knows how many i l l e g a l s come i n , and no one even h a s any v e r y good s u g g e s t i o n f o r f i n d i n g o u t . A s l o n g a s Mexico c o n t i n u e s t o b e p o o r , p e o p l e w i l l somehow c r o s s t h e Rio Grande. They c o u l d o f c o u r s e b e ex- c l u d e d by s o m e t h i n g a p p r o a c h i n g a m i l i t a r y d e f e n s e o f t h e f r o n - t i e r , b u t t h a t would s e r i o u s l y harm t h e d i p l o m a t i c and commercial a s s o c i a t i o n o f t h e U n i t e d S t a t e s and Mexico.
I n a d d i t i o n t h e r e - a r e g e n u i n e a d v a n t a g e s i n i l l e g a l i m m i g r a t i o n t o some s e g m e n t s o f u n i t e d S t a t e s a g r i c u l t u r e a n d i n d u s t r y - The il- l e g a l s h a v e n o c l a i m t o s o c i a l b e n e f i t s o r l e g a l p r o t e c t i o n i f o r some i n d u s t r i e s t h e y make a n i d e a l l a b o r f o r c e . They s u p p l y a l a b o r mar- k e t f r e e r t h a n any t h a t h a s e x i s t e d s i n c e t h e e a r l y d a y s o f t h e i n d u s - t r i a l r e v o l u t i o n . The d o m e s t i c o b j e c t i o n t o c o n t r o l a t t h e p o i n t o f employment i s s t r o n g , p a r t l y b e c a u s e o f t h e l s e l f - i n t e r e s t o f em- p l o y e r s , and p a r t l y b e c a u s e o f t h e p r i n c i p l e t h a t no employee o u g h t t o have bo i d e n t i f y h i m s e l f a n d t h e l e g a l i t y o f h i s r e s i d e n c e when a p p l y i n g f o r a j o b , s a y a s a l e t t u c e p i c k e r . I t i s s a f e t o f o r e c a s t
t h a t t h e r e w i l l b e no immediate o r e a s y s o l u t i o n t o t h e immigra- t i o n problem. The o p t i o n s have r e c e n t l y been s e t f o r t h by P h i l i p M a r t i n ( 1 9 8 1 ) .
Our f o r e c a s t s , b a s e d on a uniform method, t a k e no a c c o u n t of m i g r a t i o n . P r e s e n t l a r g e and s p o r a d i c movements h a r d l y l e n d them-
s e l v e s t o e x t r a p o l a t i o n . Our o m i s s i o n u n d e r s t a t e s t h e U n i t e d
S t a t e s p o p u l a t i o n . P u t somewhat d i f f e r e n t l y , o u r method i s equiv- a l e n t t o s u p p o s i n g t h a t t h e r e w i l l be s t a t i o n a r i t y o v e r t h e l o n g t e r m , c o u n t i n g b i r t h s , d e a t h s , and m i g r a t i o n . Any d e g r e e i n which b i r t h e s t i m a t e s a r e h i g h , a s t h e y w e l l may be, would o f f s e t t h e l a c k of p r o v i s i o n f o r m i g r a t i o n . The e s t i m a t e t h a t w e a r e u s i n g , 248 m i l l i o n i n t h e US i n 2000, compares w i t h t h e medium e s t i m a t e o f t h e ' u n i t e d S t a t e s Bureau o f t h e Census of 260 m i l l i o n and o f t h e U n i t e d N a t i o n s o f 264 m i l l i o n .
A p a r t of t h e problem everywhere i s t h e p o p u l a t i o n l e v e l f o r . t h e jumping-off p o i n t . The US Census o f 1980 c o u n t e d a b o u t 5 m i l l i o n p e o p l e more t h a n i t would have c o u n t e d w i t h t h e d e g r e e o f i n c o m p l e t e n e s s o f 1970. The l e v e l f o r t h e y e a r 2000 i s much a f - f e c t e d by w h e t h e r t h e 1980 p o p u l a t i o n i s r e a l l y 222 m i l l i o n , a s s t a t e d b e f o r e t h e c e n s u s , o r 227 m i l l i o n a s c o u n t e d , o r o v e r 230 m i l l i o n a s it c o u l d w e l l be i f one a d d s uncounted i l l e g a l s . Our f o r e c a s t e x t r a p o l a t e s t h e pre-1980 c e n s u s f i g u r e .
S t a r t i n g w i t h 227 m i l l i o n and a d d i n g m i g r a t i o n o f 500,000 p e r y e a r , which t o judge from r e c e n t s t a t i s t i c s i s t h e l e a s t t h a t s h o u l d b e a l l o w e d , would b r i n g u s t o 15 m i l l i o n ( p l u s any n a t u r a l i n c r e a s e of t h e s e ) by t h e end o f t h e c e n t u r y i n a d d i t i o n t o t h e 248 m i l l i o n t h a t i s shown i n o u r t a b l e . The t o t a l 248
+
15 = 163 i s a b o u t t h e middle o f t h e s e v e r a l o t h e r e s t i m a t e s . The U n i t e d S t a t e s and China a r e t h e two main c o u n t r i e s f o r which t i m e t o re- placement d o e s n o t p r o v i d e a s a t i s f a c t o r y s c a l e .2. POPULATION FORECASTS: ASSUMPTIONS AND ACCURACY
The h i s t o r y o f p o p u l a t i o n f o r e c a s t i n g i s more f a v o r a b l e t h a n t h a t o f t e c h n o l o g i c a l o r economic, l e t a l o n e g e o l o g i c a l , f o r e c a s t - i n g , b u t it i s s t i l l n o t good. No o n e knows what t h e p o p u l a t i o n w i l l b e 50 y e a r s h e n c e , and t h e h i s t o r y of p o p u l a t i o n f o r e c a s t i n g
i s now l o n g enough t h a t w e c a n e s t i m a t e t h e r a n g e of i g n o r a n c e .
The e x p e r i e n c e i s h e r e summarized b r i e f l y , i n s u c h a form t h a t t h e r e a d e r c a n know w i t h i n what l i m i t s t h e p r e s e n t work i s . t o b e t r u s t e d . A s i d e from b e i n g p r e s e n t e d a l o n g w i t h a n e r r o r s t a t e m e n t , t h e p r e s e n t work h a s w h a t e v e r a d v a n t a g e t h e r e i s i n a u n i f o r m p r o c e d u r e a p p l i e d t o a l l c o u n t r i e s . T h i r d l y , i t i n - v o l v e s a comparison w i t h some f i v e o t h e r f o r e c a s t s , made by t h e U n i t e d N a t i o n s , t h e World Bank, and o t h e r a g e n c i e s , and a s f a r a s p o s s i b l e w e f o r c e d c o n s i s t e n c y w i t h t h o s e o t h e r e s t i m a t e s . These t h r e e c h a r a c t e r i s t i c s - a s t a t e d c o n f i d e n c e i n t e r v a l , a s i m p l e and u n i f o r m method, and comparison w i t h t h e main f o r e - c a s t s e x t a n t and i n t h e p u b l i c domain-are t h e s p e c i a l c h a r a c - t e r i s t i c s o f t h e numbers f o r t h e y e a r s 1980-2030 g i v e n i n t h i s p a p e r .
S t a t e d i n one s e n t e n c e , t h e a s s u m p t i o n s are t h a t b i r t h r a t e s w i l l d e c l i n e t o t h e p o i n t o f b a r e r e p l a c e m e n t o f t h e p o p u l a t i o n a b o u t t h e end o f t h e c e n t u r y , and t h a t d e a t h r a t e s w i l l c o n t i n u e t o d e c l i n e f o r a l l c o u n t r i e s and d u r i n g t h e n e x t 50 y e a r s t h e y w i l l r e a c h a l e v e l somewhat below t h a t of t h e p r e s e n t l y d e v e l o p e d c o u n t r i e s .
B i r t h s a r e e x p r e s s e d i n terms o f t h e t o t a l f e r t i l i t y r a t e : t h e number o f c h i l d r e n t h a t a g i r l c h i l d c a n b e e x p e c t e d t o have.
The s o l e v a r i a b l e p a r a m e t e r o f o u r method i s t h e t i m e t o b a r e r e p l a c e m e n t , which i s t o s a y t o when each g i r l c h i l d w i l l be ex- p e c t e d t o b e a r o n e g i r l c h i l d on t h e m o r t a l i t y regime t h e n p r e - v a i l i n g . S u b j e c t t o t h i s , f e r t i l i t y was t a k e n a s f a l l i n g i n a s t r a i g h t l i n e from t h e l e v e l o f 1980 t o t h e d a t e when b a r e re- p l a c e m e n t was assumed.
T h a t t h e t i m e t o b a r e r e p l a c e m e n t i s a c o n v e n i e n t p a r a m e t e r was shown by F r e j k a ( 1 9 7 3 ) . Our own c a l c u l a t i , o n shows t h a t e a c h f i v e y e a r d e l a y i n t h e a t t a i n m e n t of r e p l a c e m e n t a d d s a b o u t 700 m i l l i o n t o t h e w o r l d p o p u l a t i o n . I f one t a k e s it t h a t r e p l a c e - ment w i l l b e a t t a i n e d i n t h e y e a r s 2000-2005 t h e n t h e u l t i m a t e w o r l d p o p u l a t i o n comes o u t t o b e 9 b i l l i o n .
S t a t i s t i c s of b i r t h s by a g e o f mother a r e n o t t o b e had f o r most c o u n t r i e s , and w e had o n l y t h e n e t r e p r o d u c t i o n r a t e e s t i - mated by t h e U n i t e d N a t i o n s t o t e l l u s t h e l e v e l . W e used t h i s a l o n g w i t h t h e model f e r t i l i t y t a b l e s d u e t o C o a l e and T r u s s e l
(1974: 185-258)
.
We allowed some c o m p l i c a t i o n i n t h e way t h a t m o r t a l i t y f a l l s . With t h e a g e s p e c i f i c d e a t h r a t e f o r 1975 a s t h e s t a r t we took i t t h a t t h e m o r t a l i t y f a l l would depend on a g e , on how m o r t a l i t y f o r a l l a g e s t o g e t h e r s t a n d s i n 1975, and on t h e t i m e when t h e change i s t a k i n g p l a c e . Thus t h e o l d e r a g e s a r e assumed t o f a l l more slowly t h a n t h e younger; t h e h i g h e r t h e e x p e c t a t i o n o f l i f e t h e s l o w e r t h e f a l l ; t h e l a t e r i n t i m e t h e slower t h e f a l l ( ~ i t t m a n and K e y f i t z 1977)
.
A l l o f o u r p r o j e c t i o n s were c a r r i e d o u t c o u n t r y by c o u n t r y and t h e t o t a l s f o r t h e s e v e r a l groups of c o u n t r i e s o b t a i n e d by a d d i t i o n . There a r e two a d v a n t a g e s , b o t h s m a l l b u t a v a i l a b l e a t no c o s t , i n p r o j e c t i n g f o r i n d i v i d u a l c o u n t r i e s and t h e n adding. --
The a d d i t i v e t o t a l , a s p o i n t e d o u t above, i s l a r g e r t h a n t h e u n i t t o t a l o b t a i n e d f o r t h e group a s a whole, and w e t h i n k t h a t i f t h e r e i s any c h o i c e i t i s more p r e c i s e . Thus f o r t h e world a s a whole w i t h r e p l a c e m e n t i n 2000-2005 t h e a d d i t i v e t o t a l f o r 2030
i s 8,093 m i l l i o n , and t h e u n i t t o t a l i s 300 m i l l i o n l e s s . The d i f f e r e n c e i s s m a l l i n - r e l a t i o n t o e r r o r , b u t w e have t h e conven- i e n c e t h a t a l l o f t h e breakdowns a r e c o n s i s t e n t w i t h one a n o t h e r ; when we add t h e c o n t i n e n t s w e g e t t h e same r e s u l t a s when we add t h e l e s s and more developed c o u n t r i e s .
We a r e i n d e b t e d t o t h e United N a t i o n s P o p u l a t i o n s D i v i s i o n f o r t h e b a s i c d a t a on which t h e s e c a l c u l a t i o n s a r e made. I n p a r - t i c u l a r t h e D i v i s i o n was k i n d enough t o p r o v i d e u s w i t h t h e a g e d i s t r i b u t i o n s , t h e n e t r e p r o d u c t i o n r a t e s , and t h e e x p e c t a t i o n s o f l i f e f o r t h e c o u n t r i e s o f o v e r 250,000 p o p u l a t i o n t h a t t h e y and we r e c o g n i z e i n advance o f t h e i r own p u b l i c a t i o n .
Our a d j u s t a b l e p a r a m e t e r , t h e t i m e t o r e p l a c e m e n t , i s no e a s i e r f o r us t o know t h a n f o r anyone e l s e . W e have examined t h e p r o j e c t i o n s t o t h e y e a r 2000 made by a number of a g e n c i e s , and how t h e s e f a l l i n r e l a t i o n t o t h e s e v e r a l t i m e s t o replacement.
Thus i n t h e c a s e of Egypt, replacement by 2000-2005 - --- w o u l a g i v e a 2000 p o p u l a t i o n of 61.3 m i l l i o n , a n d b y 2 0 1 5 - 2 0 2 0 , 1 5 y e a r s l a t e r ,
. . . - -- -
would g i v e 65.8 m i l l i o n f o r t h e y e a r 2000. The ~ n - i t s ~ a t i b n s , t h e World Bank, and t h e United S t a t e s Bureau of t h e Census a l l gave p o p u l a t i o n s f o r t h e y e a r 2000 t h a t a r e between t h e s e numbers w h i l e Donald Bogue (1979) and Littman and ~ e y f i t z (1977) f a l l
somewhat below t h i s r a n g e .
2.1. Check A g a i n s t O t h e r F o r e c a s t s
There e x i s t now a t l e a s t f i v e p r o j e c t i o n s o f p o p u l a t i o n f o r t h e c o u n t r i e s o f t h e w o r l d by t h e U n i t e d N a t i o n s , t h e P o p u l a t i o n R e f e r e n c e Bureau, t h e World Bank, t h e US Bureau o f t h e Census, and t h e Community a n d Family S t u d y C e n t e r o f t h e U n i v e r s i t y o f Chicago. Most o f them go o n l y t o t h e y e a r 2000, and t h a t o f t h e Bureau o f t h e Census c o v e r s o n l y t h e l a r g e s t c o u n t r i e s . They a r e f a r from i n d e p e n d e n t o f o n e a n o t h e r , a s i s shown i n t h e i r docu- m e n t a t i o n and i n t h e f a c t t h a t t h e i r r e s u l t s a g r e e c l o s e l y . But e a c h o f them c o n t r i b u t e s some e l e m e n t s o f judgement by competent demographers, and w e made u s e of a l l o f them i n d e t e r m i n i n g o u r own f o r e c a s t .
F o r e a c h o f t h e c o u n t r i e s w e p r o j e c t e d w i t h t i m e s t o r e p l a c e - ment from 1990-1995 u p t o 2020-2025. Wethen examined t h e f i g u r e s
f o r t h e y e a r 2000 i n c o m p a r i s o n w i t h t h e f i v e o u t s i d e f o r e c a s t s . W e c h o s e a t i m e t o r e p l a c e m e n t t h a t gave u s a f i g u r e f o r 2000 a b o u t t h e c e n t e r o f t h e d i s t r i b u t i o n o f t h e o u t s i d e f o r e c a s t s . A few i n s t a n c e s w i l l show t h e c o m b i n a t i o n o f c a l c u l a t i o n and judgement.
2.2. The L a r g e s t C o u n t r i e s
I n t h e c a s e o f N i g e r i a t h e l o w e s t o f t h e f i v e e s t i m a t e s f o r t h e y e a r 2000 was 121.6 m i l l i o n , by t h e Community and Family S t u d y C e n t e r o f t h e U n i v e r s i t y o f Chicago. The h i g h e s t was t h a t o f t h e World Bank, w i t h 157.1 m i l l i o n . Between w e r e t h e o t h e r t h r e e
s o u r c e s . W e n o t e d t h a t t h e u l t i m a t e s t a t i o n a r y p o p u l a t i o n f o r e - c a s t by t h e World Bank was 435 m i l l i o n , and though t h i s was a r e a s o n a b l e e x t r a p o l a t i o n from p a s t growth, it seemed t o o h i g h on e c o l o g i c a l grounds. One c a n h a r d l y i m a g i n e N i g e r i a b e i n g a b l e t o f e e d s u c h a p o p u l a t i o n , o r s e l l t h e manufactured goods t h a t would buy food f o r them. W e p u t N i g e r i a ' s t i m e t o r e p l a c e m e n t a t 2015- 2020 and t h i s g i v e s i t 134 m i l l i o n f o r t h e y e a r 2000. T h a t i s a l m o s t e x a c t l y what t h e U n i t e d S t a t e s Census Bureau gave, b u t i s c o n s i d e r a b l y below t h r e e o t h e r e s t i m a t e s .
C h i n a ' s p o l i c y h a s gone t h r o u g h v a r i o u s p h a s e s , s t a r t i n g i n t h e 1950s w i t h o f f i c i a l o p p o s i t i o n t o any b i r t h c o n t r o l n o t i m - m e d i a t e l y i n a i d o f t h e h e a l t h o f mother and c h i l d , and e v o l v i n g
t o t h e u l t i m a t e v e r y f u l l r e c o g n i t i o n o f t h e p o p u l a t i o n problem
i n t h e c o n s t i t u t i o n o f 1978. Any i d e o l o g i c a l o p p o s i t i o n t o b i r t h c o n t r o l h a s g i v e n way t o p r a c t i c a l n e c e s s i t y i n t h e f a c e o f econ- omic handicap of a f a s t m u l t i p l y i n g p o p u l a t i o n . The regime i n B e i j i n g i s d e t e r m i n e d and e f f e c t i v e ; i t h a s gone t o enormous p a i n s t o persuade c o u p l e s t o have no more t h a n one c h i l d , a t most two.
T r a v e l l e r s r e p o r t s u c c e s s i n t h e a r e a s t h a t t h e y v i s i t e d , though t h e y have n o t been a b l e t o v i s i t a random sample of v i l l a g e s .
Most o f t h e s e r i e s a v a i l a b l e t o u s p o i n t t o a Chinese popu- l a t i o n of 1,200 m i l l i o n o r l e s s by t h e e n d o f t h e c e n t u r y . To a s - s i g n i t replacement by t h e y e a r 1990-1995 shows 1,361 m i l l i o n by 2000, which i s e v i d e n t l y h i g h . Even i f r e p l a c e m e n t i s s e t a t 1980, i . e . , immediately, t h e 2000 p o p u l a t i o n would be 1,268 m i l - l i o n , which i s h i g h e r t h a n any of t h e e s t i m a t e s e x c e p t t h a t o f t h e Bureau of t h e Census and r e a c h e s 1,453 m i l l i o n by 2030 and
1,617 m i l l i o n by 2075. Unless China i s below replacement f o r a c o n s i d e r a b l e p e r i o d of t i m e , i t w i l l have a n u l t i m a t e p o p u l a t i o n g r e a t e r t h a n 3.6 b i l l i o n .
When government makes p o p u l a t i o n t h e s u b j e c t of a c t i v e - p o l i c y , i t p l a c e s s p e c i a l d i f f i c u l t i e s i n t h e w a y o f one who would produce u n c o n d i t i o n a l f o r e c a s t s . Any f o r e c a s t t h e n becomes a judgement on t h e f e a s i b i l i t y and on t h e s u c c e s s o f t h e government's p o l i c y . Aside from t h e u s u a l d i f f i c u l t i e s , t h e f o r e c a s t e r h a s t o s a y by
i m p l i c a t i o n whether what t h e government i s d o i n g c a n succeed- whether among o t h e r t h i n g s t h a t government w i l l s t a y i n power, and whether it w i l l be a b l e t o p e r s i s t i n i t s p o l i c y i f it does.
The p o p u l a t i o n f o r e c a s t e r c a n h a r d l y s h o u l d e r such a burden o f judgement, g i v e n t h a t whatever s k i l l h e h a s l i e s i n t h e c a p a c i t y t o e x t r a p o l a t e p a s t f i g u r e s o f b i r t h s , d e a t h s , and m i g r a t i o n .
I n t h e f a c e of a l l t h e d i f f i c u l t i e s , and e s p e c i a l l y of t h e r a p i d changes t h a t China h a s s e e n i n many f i e l d s i n c l u d i n g t h e d i s s e m i n a t i o n of b i r t h c o n t r o l , t h e b e s t t h a t we c a n do i s t o t a k e i t t h a t t h e number o f b i r t h s w i l l n o t r i s e s u b s t a n t i a l l y i n t h e f u t u r e from where it now i s . From a n a l l - t i m e h i g h p o i n t of 29 m i l l i o n i n 1963 t h e r e h a s been a n i r r e g u l a r d e c l i n e t h a t b r o u g h t t h e l e v e l t o 1 7 m i l l i o n i n t h e l a t e 1970s. We do n o t t h i n k t h a t it w i l l be allowed t o rise s u b s t a n t i a l l y above t h i s , even though f a m i l i e s o f c o n s i d e r a b l y l e s s t h a n two c h i l d r e n w i l l
be r e q u i r e d t o p r e v e n t a r i s e , g i v e n t h e v e r y young a g e d i s t r i - b u t i o n . I f t h e h i g h e s t t h a t t h e b i r t h s a r e allowed t o a v e r a g e d u r i n g t h e n e x t 50 y e a r s i s 20 m i l l i o n , t h e n we c a n s a y t h a t t h e p o p u l a t i o n w i l l be below t h e s u r v i v o r s o f t h e one b i l l i o n b i r t h s p l u s t h e p r e s e n t p o p u l a t i o n of one b i l l i o n by t h e y e a r 2030.
Using a l i f e t a b l e of 70-years e x p e c t a t i o n d e r i v e d from Coale and Demeny (1966) we f i n d f o r t h e y e a r 2030 a p o p u l a t i o n o f 1,423 m i l l i o n s . For t h e t u r n of t h e c e n t u r y w e f i n d 1,223 m i l l i o n . T h i s l a t t e r i s s t r a d d l e d by 1,329 m i l l i o n of t h e United S t a t e s Bureau of t h e Census, and by 1,190 of t h e United N a t i o n s . China i s t h e one c o u n t r y f o r which w e have been compelled t o d e p a r t from o u r uniform method. I f t h i s i s i n e r r o r it i s on t h e high s i d e , t o judge from t h e v e r y c o n v i n c i n g s t a t e m e n t s o f t h e a u t h o r - i t i e s .
F o r e c a s t s f o r I n d i a a r e a b o u t t h e b i l l i o n mark f o r 2000, w i t h t h r e e below t h e b i l l i o n and two above. Assuming replacement by 2000-2005 b r i n g s o n e . - t o 1,020 m i l l i o n by 2000, which i s what w e a r e u s i n g .
The USSR p r e s e n t s a p a r t i c u l a r l y s i m p l e c a s e , w i t h a l l f i v e of t h e a g e n c i e s i n t h e narrow r a n g e from 306 m i l l i o n t o 312 m i l - l i o n . Our own comes o u t t o 310 m i l l i o n .
The United S t a t e s i s assumed t o have f e r t i l i t y g e n t l y s l o p - i n g upwards towards r e p l a c e m e n t , and on o u r e s t i m a t e comes o u t t o 248 m i l l i o n by 2000. But t h i s i s u s i n g t h e pre-census f i g u r e of 2 2 2 m i l l i o n f o r 1980. Our work t a k e s no a c c o u n t o f immigra- t i o n . I t i s s a f e t o g u e s s t h a t f u t u r e numbers w i l l be 10, per- haps 15, m i l l i o n h i g h e r t h a n o u r e s t i m a t e .
I n d o n e s i a i s t h e s u b j e c t o f much d i s a g g r e g a t i o n on t h e p a r t o f t h e s e v e r a l a g e n c i e s , which r u n a s low a s 194 m i l l i o n , and a s h i g h a s 2 2 2 m i l l i o n . O u r method, w i t h replacement by 2000-2305, g i v e s 2 2 2 m i l l i o n f o r I n d o n e s i a i n t h e y e a r 2000. T h i s p u t s u s a t t h e h i g h end o f t h e r a n g e , which seems j u s t i f i e d by t h e 1981 Census.
On Japan t h e r a n g e o f a g e n c i e s was from 129 t o 133, a l m o s t a s narrow a s t h a t f o r t h e USSR. Our method ended up i n t h e mid- d l e , w i t h 131 m i l l i o n . Japan h a s been e x c e p t i o n a l t h r o u g h o u t
i t s h i s t o r y , and t h i s agreement s h o u l d n o t e x c i t e o v e r - c o n f i d e n c e i n t h e common f o r e c a s t . A p p a r e n t l y Tokugawa J a p a n (1603-1867) showed c r u d e b i r t h r a t e s i n t h e r a n g e 15 t o 30 p e r thousand.
T h i s was f o l l o w e d by r i s i n g r a t e s up t o 1919, f a l l i n g r a t e s t o 1920-1935, and from 1950 a r a p i d f a l l i n b o t h f e r t i l i t y and mor- t a l i t y (see, Mosk 1979:19). The h i s t o r i c a l e x c e p t i o n s of J a p a n and F r a n c e , a s w e l l a s t h e v a r i a t i o n w i t h i n t h e c o u n t r i e s of Europe shown by t h e P r i n c e t o n s t u d y , undermine t r u s t i n t h e demographic t r a n s i t i o n a s a f o r e c a s t i n g i n s t r u m e n t . .
2.3. Accuracy of F o r e c a s t s
A f o r e c a s t e r must r e s p e c t t h e unknown f o r c e s t h a t d e t e r m i n e t h e f u t u r e and b e modest c o n c e r n i n g h i s own powers t o p e n e t r a t e t o t h e s e . Such modesty i s t a u g h t by p a s t e x p e r i e n c e . E a r l i e r f o r e c a s t s c a n i n d i c a t e t h e bounds t h a t s h o u l d b e s e t on p r e s e n t o n e s , and t h e bounds t u r n o u t t o be wide. One method f o r a s s e s s - i n g e r r o r i s d e s c r i b e d e l s e w h e r e ( K e y f i t z 1981) and a b r i e f sum- mary w i l l s u f f i c e f o r t h e p r e s e n t p u r p o s e .
The measure o f a c c u r a c y u s e d is t h e d e g r e e t o which t h e f o r e c a s t i m p l i e d a n n u a l r a t e o f i n c r e a s e e x c e e d s t h e r e a l i z e d r a t e o f i n c r e a s e . F o r example, Whelpton i n 1936 f o r e c a s t t h e p o p u l a t i o n o f t h e y e a r 1970 a t 155 m i l l i o n . I n 1936 t h e U n i t e d S t a t e s p o p u l a t i o n w a s 127 m i l l i o n , s o t h a t t h e r a t e o f i n c r e a s e i m p l i e d was 0.57 p e r c e n t . A c t u a l l y t h e p o p u l a t i o n grew t o 203 m i l l i o n , s o t h a t t h e r e a l i z e d r a t e o f i n c r e a s e was 1.35 p e r c e n t . T h a t makes o u r measure o f t h e i n a c c u r a c y o f t h e f o r e c a s t t h e d i f - f e r e n c e between t h e s e two numbers, i . e . , 1.35
-
0.57 = 0.78 p e r - c e n t a g e p o i n t s . Such d i f f e r e n c e s c a n b e a v e r a g e d i n many ways, o f which two t h a t come t o mind a r e t h e root-mean-square and t h e mean a b s o l u t e v a l u e . A round number t h a t r o u g h l y d e s c r i b e s t h e r e c o r d o f some 1,100 f o r e c a s t s i s 0.3 p e r c e n t a g e p o i n t s i n t h e mean a b s o l u t e e r r o r . Again s p e a k i n g r o u g h l y , t h i s t e l l s u s t h a t o n e c o u l d s a f e l y b e t e v e n odds t h a t t h e r e a l i z e d r a t e of i n c r e a s e w i l l t u r n o u t t o b e w i t h i n 0.3 p e r c e n t a g e p o i n t s of t h e f o r e c a s t r a t e o f i n c r e a s e .I n a p p l i c a t i o n t o o u r own f o r e c a s t f o r t h e R e p u b l i c o f Korea i n t h e y e a r 2000, w e s a y t h a t t h e p o p u l a t i o n w i l l b e 51.8 m i l l i o n
a g a i n s t a 1980 p o p u l a t i o n o f 39.1 m i l l i o n , i . e . , a r a t e of i n c r e a s e of 1.42 p e r c e n t p e r y e a r . Adding and s u b t r a c t i n g 0.3 p e r c e n t a g e p o i n t s t o t h i s we can b e t even odds t h a t t h e r e a l i z e d r a t e o f i n c r e a s e w i l l be between 1.12 and 1.72 p e r c e n t p e r y e a r , which would g i v e f o r t h e y e a r 2000 a r a n g e i n t h e number o f
p e o p l e from 48.8 t o 54.9 m i l l i o n . For 2030 t h e l i m i t s would be 55.9 , t o 75.2 m i l l i o n . T h i s r a n g e may seem wide, y e t it i s based on t h e a v e r a g e o f t h e e r r o r s o f p o p u l a t i o n f o r e c a s t s f o r t h e s e v e r a l c o u n t r i e s o f t h e world.
Two c o n s i d e r a t i o n s p e r m i t some narrowing o f t h i s e s t i m a t e o f e r r o r . One i s t h a t r e c e n t f o r e c a s t s have been more p r e c i s e t h a n t h o s e made e a r l i e r . The o t h e r i s t h a t on t h i s measure o f a c c u r a c y s l o w l y growing p o p u l a t i o n s a r e more p r e c i s e t h a n f a s t e r growing ones. These two c o n s i d e r a t i o n s might a t t h e v e r y o u t s i d e h a l v e t h e e s t i m a t e o f e r r o r , which would be e q u i v a l e n t t o s a y i n g t h a t t h e b e t t i n g odds t h a t t h e Korean p o p u l a t i o n w i l l be between 55.9 and 75.2 m i l l i o n i n 2030 a r e n o t 2:1 b u t r a t h e r 20:l.
T h i s c a l c u l a t i o n must be modifed i n a p p l i c a t i o n t o t h e world p o p u l a t i o n . The e s t i m a t e o f e r r o r was based on i n d i v i d u a l coun- t r i e s , and a g g r e g a t e s o f c o u n t r i e s w i l l have l e s s e r r o r i n t h e measure i n which o f f s e t t i n g c a n be e x p e c t e d . The second p o i n t i s advanced w i t h m o r e h e s i t a t i o n . I f we t h i n k t h a t t h e e v o l u t i o n o f m o r t a l i t y c a n n o t b u t be such t h a t b a r e r e p l a c e m e n t w i l l b e o b t a i n e d w i t h i n a l i m i t e d span o f y e a r s , t h e n w e c a n hope t h a t t h a t span o f y e a r s w i l l p r o v i d e a c o n f i d e n c e i n t e r v a l on which w e c o u l d b e t . I f w e c o n s i d e r t h a t we a r e coming t o such a p o i n t i n t h e e v o l u t i o n o f p o p u l a t i o n t h a t r e p l a c e m e n t i s 95 p e r c e n t c e r t a i n a s a world a v e r a g e w i t h i n 20 t o 40 y e a r s , t h e n w e c a n , c o r r e s p o n d i n g l y , b e t 20 t o 1 t h a t t h e world p o p u l a t i o n by t h e y e a r 2030 w i l l be between 8 and 11 b i l l i o n , t o u s e round f i g u r e s .
To summarize t h e s t u d i e s of e r r o r :
1. A round f i g u r e t h a t summarizes t h e e r r o r o f p a s t p r o j e c - t i o n s i s t h a t t h e y have a n a v e r a g e a b s o l u t e d e p a r t u r e from t h e s u b s e q u e n t performance of 0 . 3 p e r c e n t a g e p o i n t s o f i n c r e a s e p e r y e a r .
2. F a s t e r growing p o p u l a t i o n s have l a r g e r e r r o r , s a y 0.5 p e r c e n t a g e p o i n t s , w h i l e t h o s e t h a t a r e n e a r s t a t i o n a r i t y show a b o u t 0.2 p e r c e n t a g e p o i n t s .
3. The s k i l l and c a r e i n c o p o r a t e d i n t h e f o r e c a s t seem t o have less r e l a t i o n t o a c c u r a c y t h a n t h e t i m e when t h e f o r e c a s t was made. F o r e c a s t s t e n d e d t o b e low i n t h e 1940s f o r d e v e l o p e d c o u n t r i e s b e c a u s e t h e e x t e n t o f t h e baby boom was n o t f o r e s e e n ,
f o r t h e less d e v e l o p e d b e c a u s e o f t h e s u b s e q u e n t u n a n t i c i p a t e d f a l l o f m o r t a l i t y .
4 . S i z e o f c o u n t r y , and w h e t h e r r i c h o r p o o r , h a s a l m o s t no i n d e p e n d e n t e f f e c t o n a c c u r a c y f o r c o u n t r i e s o f g i v e n r a t e o f i n c r e a s e .
5. A most i m p o r t a n t c o n s t a n c y i s w i t h t h e p r o j e c t i o n span- a c c u r a c y o n o u r measure seems u n a f f e c t e d by w h e t h e r one i s f o r e - c a s t i n g 5 o r 20 y e a r s a h e a d . E x t r a p o l a t i o n o f t h i s c o n s t a n c y p e r m i t s s t a t e m e n t s a b o u t t h e e r r o r o f f o r e c a s t s 30 o r more y e a r s a h e a d , on which w e have no d i r e c t e x p e r i e n c e .
6. The c o n c l u s i o n a r i s i n g from t h i s i s t h a t f o r t h e n e x t 10 t o 20 y e a r s w e c a n p r o v i d e f o r e c a s t s o f r e a s o n a b l e a c c u r a c y ; beyond t h a t t h e p o p u l a t i o n i s e s s e n t i a l l y unknowable. T h a t s h o u l d b e t a k e n i n t o a c c o u n t i n any c o n c l u s i o n s drawn o n o u r p r o j e c t i o n s f o r t h e n e x t 50 y e a r s . They a r e t o b e c o n s i d e r e d i l l u s t r a t i v e , s u i t e d t o i n c o r p o r a t i n g i n h y p o t h e t i c a l s c e n a r i o s .
7. A q u a l i f i c a t i o n on t h e above i s t h a t p r o j e c t i o n methods may now b e b e t t e r t h a n t h e y w e r e i n t h e 1940s and 1950s. C e r -
t a i n l y o v e r t h e 20 o r s o y e a r s t h a t it i s p o s s i b l e t o f o l l o w t h e r e i s a c l e a r downtrend i n t h e e r r o r . F o r e c a s t s i n t h e 1940s showed a mean d e p a r t u r e of a b o u t 0.7 p e r c e n t a g e p o i n t s ; t h o s e o f t h e 1960s a mean d e p a r t u r e of less t h a n 0.3 p e r c e n t a g e p o i n t s . W e may c a u t i o u s l y a c c e p t t h e downtrend a s r e a l , e v e n though a
l o n g e r s e r i e s i s needed b e f o r e one c a n b e s u r e .
8. F o r e c a s t s f o r a r e a s w i t h i n c o u n t r i e s have been s u b j e c t t o much more e r r o r t h a n f o r e c a s t s f o r e n t i r e c o u n t r i e s . T h a t e n c o u r a g e s u s t o t h i n k t h a t f o r e c a s t s f o r g r o u p s o f c o u n t r i e s and f o r t h e w o r l d may w e l l be b e t t e r t h a n t h e n a t i o n a l f o r e c a s t s on which most o f o u r o b s e r v a t i o n s o f f o r e c a s t i n g e r r o r have been made.
