Dr. Toshio Kuroda
Director Emeritus
Population Research Institute
Nihon University, Japan

Trends of socio-economical conditions and population factors such as fertility, and mortality and mobility of the population are closely related. The links between them, however, are complex and varied, and also dependent upon the specific circumstances related to individual countries.

In post-war Japan, demographic factors have shown dramatic changes not only in fertility behavior and mortality reduction, but also in migratory movements. In particular, internal migration within Japan should be paid specific attention because of the rapid change in volume and directional movement.
This reveals that migratory movement affected not only the size of the local population, but also the diversified effects on birth and death rates.

Migration may not necessarily be important in projecting the future population of Japan as a whole because of the negligible number of outward (overseas) migration. However, in the case of the projection of the local population, migration trends are important factors that affect local population in terms of not only total population size, but also in fertility and mortality.

We must recognize the clear implications of the contemporary population projection system, which is quite advanced in technique and data collection. Therefore, now this can provide us appropriate data and measures necessary to cope with the radically changing age structure.

As far as the national population is concerned, population projection is reasonably dependable. On the other hand, however, local population projection also helps local government to adjust a type of "Comprehensive City Plan" as guiding light to policy measures. In contrast, projected figures are usually less reasonable than those of a national population projection. In particular, during Japan's rapid economic growth following World War II, tremendous migratory movements took place.

Agricultural and less developed prefectures, as well as many local governments, lost a large amount of the young population, and thus showed a population decline. On the other hand, several large, urbanized areas absorbed a tremendous amount of migrants. It should be noted that such large migratory movements resulted in serious demographic issues; such as fertility decline and mortality rise in rural areas, and high fertility with low mortality in urban areas. These drastic changes were caused by the heavy migration composed of a young population (either just married or just prior to marriage and also characterized by low mortality among young migrants), which left a majority of the elderly population in rural areas.

In this case, from the standpoint of the population projection, such large groups of migrants composed of the young adult population are expected to bring about an additional determining factor in increasing population size through marriage and the bearing of children. As a result, this type of secondary effect due to young migrants will be a difficult area to take into account when projecting a local population.

2. Population Size and Population Projection in Japan

Population projections for Japan are composed of three different categories: national, prefectural, and local self-governing bodies, which include city, town, and village.

Even though migratory movements often tend to disturb population projection, prefectural population size is large enough in order to conduct future population projections. However, in the case of a small local population with less than 100,000 inhabitants, much more difficult factors are present. It should be noted here that local governments are legally regulated by the central government when creating the "Comprehensive Development Plan" every ten years, which is solely based upon future population projections. In that case, local governments are usually skilled in the ways of conduction of population projection works.

Another point to make in regard to population projection of small, local populations is the frequent change of the size and borders through annexation and absorption. For example, in 1950 the number of towns and villages was more than 10,000, but by 2000 this number declined twenty five percent in less than half a century to 2500 (a quarter). This kind of reduction of the local government may be another reason to conduct a population projection, which will also be designed to correspond with the "Comprehensive City Plan."

Nevertheless, a local population projection is greatly affected not only by socio-economic change, but also radical change in demographic factors, including fertility and movement. In addition, the extent, speed, and level of those demographic factors are quite different in each area. Inevitably, the future assumptions of population variables should be carefully made according to a detailed analysis of each particular area.

3. Future Population Projection of Prefectures

In Japan, the prefecture is the largest autonomous administrative body. There are 47 prefectures in Japan, and each prefecture's population is quite diversified, ranging from 600,000 to 12 million inhabitants. However, prefectural population size is perhaps enough to make a relatively reasonable projection. In particular, however, it should be noticed that the stream of migration is extremely difficult to predict.

The Cohort Components method is usually used in Japan. The population is separated by gender and age taken as a base population to which, four variables are applied. These four variables include: base population values of future fertility, survival ratio, net migration rate, and sex ratio at birth.

Furthermore, the projected national population does not necessarily correspond with the total number of the projected population of each prefecture because national population projections do not account for internal migration movements. Statistical adjustment is made in order to make the total projected population of each prefecture coincide with the national population projection, which is made separately.

Each prefecture constructs its own population projection. On the other hand, however, the government office responsible for making population studies conducts nation wide population projections in much larger terms than that of prefectural projections.

4. Local Population Projection-City, Town, and Village

Finally, small population areas including city, town, and village will be discussed. In view of effective development, the preparation of the "Comprehensive City Plan" is legally required every ten years. The future population projection is instrumental in implementing policies and programs shown in the "Comprehensive City Plan."

One of the crucial points in relation to the local population projection is the difficulty in obtaining exact data of the internal migration between local governments. The "In-and-Out Migration Law" controls migratory movement from the standpoint of election law. Of course, there is a lack of statistical accuracy. One way of solving this problem, the "Cohort Change Rate" method was applied by using a five-year age group of population census results and by gender derived from the national population of censuses in 1990 and 1995. It is understood that within each city, town, and village in the five-year period from 1990 to 1995, mortality by gender, five-year age groups, migration trends, and also fertility levels will continue to rise in the future. The projection covers thirty years from 1995 to 2025, figures shown for every five years.

Population aged 0-4 years old was calculated by using a ratio of the population aged 0-4 years by gender to the female population aged 15-49 years old enumerated in the 1995 national population census.

The female population aged 15-49 in projected years has estimated by the following method. Population aged five years and older by age and gender has assumed that morality and also the difference between in-migrants and out-migrants observed in the period 1990 to 1995 will be constant in the future. In other words, the ratio of the population of the five-year age group by gender in 1995 to the population of the less than five-year age group in 1990 is used to calculate assumed figures of each five- year age group population.

The example of the local population projection, including city, town, and village was presented here based upon the 1990 and 1995 national population census results. Particular attention should be paid to the reliability and accuracy of these local population projections. First, socio-economic and political changes and their effects, which occurred in only the five-year period, should be taken into account, and there was assumed to be no change adjusted.

Secondly, there is frequent change of administrative areas of local governments due to annexation and or other reasons.

Thirdly, in view of the specific nature of the individual, local governing authorities, separate population projections are also recommended based on the detailed studies of population trends and socio-economic planning. For example, if a large scale development of public housing is suddenly implemented in a small, local community, the size of the population, and also age and gender composition, will be greatly affected, which would not coincide with projected figures. In such a case, it is recommended that the population projection be revised in order to take into account this new data. On the other hand, there are a large number of local governmental bodies where population decline and aging have become accelerated. In this case, population projection is likely to be affected by the decision maker's attitude or their policy plan to take positive action in regard to socio-economic development.

There are several different policies for population projection between national population projection and local, small population projection. Usually, the short period beyond the immediate few years, and five to ten years is covered by the local population projection, whereas the national population projection covers a longer period, for example, twenty, thirty, and fifty years respectively. Occasionally, the long-range projection of world population over the period of 1995-2150 is made by the United Nations.

In addition, the local population projection is characterized by "target" prediction in which future predictions or plans of decision makers, including the mayor, is incorporated. In general, however, the national population projection is designed to be as much realistic as it is demographically scientific.

Finally, local, small populations are frequently affected by temporary economic or social events, which are not taken into account in advance. It may be recommended that in addition to population projection required by law, a detailed survey on economic, social, and demographic events should be made individually designed in order to be utilized for future population projections.

Concluding Remarks

The necessity and the effectiveness of future population projections in economic and social development planning are universally recognized in all countries and also by international organizations. One of the reasons is that population variables are basic factors affecting the socioeconomic conditions of people's lives. For example, high rates of population increase of between three and four percent a year exceeds the food production rate. Also, baby-boomers resulting from high birth rates necessitate tremendous increases in educational expenditures, etc. On the other hand, it should be recognized that socio-economic effects caused by a population change are expected to influence population trends. In this way population change and also its reaction is becoming greater in magnitude.

The projections are prepared on the basis of assumed trends in the components of fertility, mortality and migration, and hence on the growth of the population. Similarly, projections provide a means of studying the effects of changes in fertility and mortality on the age structure, etc.

I would like to say finally that exactly speaking, projections are not predictions, nor forecasts, but statements of what the size, gender, and age of the population would be at specific times in the future if birth and death rates, as well as migration were to follow certain specified trends (as per assumptions). However, population size and age composition enumerated in the census year are basic, initial population for projection for ten, twenty years or much larger period in the future.

The crucial issue of contemporary future population projection is based on enormous change of demographic events, which are expected to seriously affect, social, economic, and political systems. However, unfortunately complete projections of future social and economic change are not realistically attained.