Demography

Map of the world population by country (2009).

The demography (from the Greek δήμος dēmos 'people' and γραφία graphy 'trace, description&# 39; -study of the population) is a science that statistically studies human populations; its dimension, structure, evolution and general characteristics, as well as the specific processes that determine its formation, conservation and disappearance. Such processes are those of fertility, mortality and migration: emigration and immigration. The variety of combinations of these phenomena, interdependent among themselves, supposes the speed of the changes in the population, both in its numerical dimensions and in its population structure.

Demography is an interdisciplinary scientific field that studies population size, composition, and spatial distribution, as well as changes in the population and the components of those changes, such as fertility, mortality, and migration. Science has evolved thanks to the theoretical and methodological contributions of different disciplines, such as sociology, economics and geography.

History of demography

Although demographic concerns have been present since ancient times in many civilizations -to preserve their permanence and their military and labor capacity- we see for the first time during a reaction in the Roman Empire to a demographic problem. Because of the civil wars of the I century a. C., there was a birth crisis to which César Augusto reacted by approving in the year 18 a. C. the lex Iulia de maritandis ordinibus -Iulia matrimonial law- which sought to promote marriage and birth rates in addition to penalizing unmarried and childless couples.

But it will be the historian, sociologist, demographer and humanist Ibn Khaldun (1332-1406) who is recognized as the father of demography, since he was the first to consider statistical data in his studies to represent them and obtain new data more representative.

The Englishman John Graunt (1620-1674) is also considered one of the first demographers and founder of biostatistics and the forerunner of epidemiology with the publication, in 1662, of his work Natural and Political Observations Made upon the Bills of Mortality.

The German Johann Peter Süssmilch (1707-1767), statistician and demographer, developed life tables, used in actuarial sciences and insurance, was cited by Malthus.

In 1798 Thomas Robert Malthus, the father of modern demography along with Graunt, published his classic work, Essay Concerning the Principle of Population, in which, among other things, he warned of the constant tendency of the growth of the human population superior to the one of the production of foods, and informed of the different factors that influenced on this growth: the war, the famine, the illness and the contraception. His alarmist predictions gave him and still give him fame and recognition.

But Malthus was wrong in his time predictions about the date of the Malthusian catastrophe but not in his analysis of population growth. Science has succeeded in increasing food production, especially in industrialized countries, where many of they have become exporters of agricultural products (to which the so-called transgenic foods have been incorporated). But the real problem today is, although it may seem paradoxical, in the overproduction of food and not because there is no need for it, especially in poor countries, but because those who need it most cannot acquire it.

We must not forget that the possibility of studying the population arises with statistics and, also, with the preparation of regular and universal censuses. For this reason, a distinction is made between pre-statistical and statistical epochs. However, the attempt to take a census of the population to find out their number, and collect taxes, is very old; from the Romans to the Modern Age there is news in this sense. But the technical difficulties for a rapid count did not allow the performance of such studies. Despite the advances of the XX century, the same situation occurs in many underdeveloped countries or with political and military conflicts.

The study of the ancient population is done through indirect sources: series, tithes, counts of fires or a supposed optimal demographic density, to be able to live in a territory, when the studied populations are very old. And in the Ancient Age, with the development of the Roman Empire, the magistracy of the censor arose, in charge of making population inventories (censuses) for tax purposes throughout the imperial territory.

There are some data from antiquity that allow us to observe a growth curve, which in recent years follows a geometric proportion. Thus, it is estimated that about 2000 years ago there was a total population close to 250 million people. Almost a million years had been needed to reach that figure, if we accept that date as the appearance of the first representatives of our species.

A millennium and a half later, around 1650, the earth's population was already double, and four times more, three centuries later, in 1850. From that date, when the industrial revolution began on a large scale, the figures they have shot.

We then find that in the course of just one hundred years, in 1950, and after the great bloodletting caused by the two world wars, estimates give a total of 2.5 billion inhabitants, that is, two and a half times more than in 1992. To increase another two billion it takes only 25 years and by the end of the XX century, another twenty-five years counting from that date our planet will have more than 6000 million people. Today the barrier of 7 billion inhabitants has already been overcome and it continues to grow. According to some authors, this quantitative increase may be disproportionate, taking into account that the available resources do not increase in the same proportion.

Types of demographics

The two types or parts of demography are interrelated, and the separation is somewhat artificial, since the study objective is the same: human populations.

• Static demography: It is the part of the demographic that human populations study at a time determined from a point of view of dimension, territory, structure and structural characteristics.

1. La dimension is the number of persons normally residing in a geographically well-delimited territory.
2. The territory is the place of residence of people who can globalize or disaggregate as, for example, a nation, a region, a province, a city, a municipality, etc.
3. La structure of a population is the classification of its inhabitants according to person variables. According to the United Nations, these variables are: age, sex, marital status, place of birth, nationality, spoken language, level of instruction, economic level and fertility.

• Dynamic demography: It is part of the demographic that human populations study from the point of view of evolution over time and the mechanisms by which the dimension, structure and geographical distribution of populations are modified. Examples of such mechanisms include birth, mortality, family, fertility, sex, religion, age, education, divorce, ageing, migration, work, emigration and immigration.

Its expression is the demographic tables, which are the numerical and graphical statistical data. The administrators use the total census (actual (every ten years) or monthly or annual samples (estimated). They have to be designed in such a way that not only descriptive statistics can be established, but also cross-demographic analyses can be performed. An example are: annual salaries and ages or the distribution by salaries, by social classes, in the nation and in a community, by households and families, etc. General topics or basic variables are wealth, power and social mobility.

Statistical data on populations are also subjected to predictive or future analysis: interpolations, extrapolations, time series, logistic curves, growth patterns according to type of society, patterns of decline due to natural disasters or epidemics or wars, etc..

Since the 19th century it was discovered that the graph of population growth follows the shape of an elongated S, of rapid growth or exponential model, reaches a turning point and continues with a smooth growth, and is a reflection of the transition from an agricultural society to an industrial society: the reduction in the number of births and the increase in the population that is in the third age.

Demographic theories

Demographic transition

According to the demographic transition model, changes in a population have three components: births, deaths, and migration. The demographic transition as a process diminishes the effect of four major sociodemographic risks: high mortality, high fertility, accelerated population growth, and young age structure.

With greater or lesser intensity and speed, all the countries of Latin America have begun the process of demographic transition, because they have all begun to reduce their fertility and mortality rates.

Celade has developed topologies to identify the sociodemographic risks that countries are going through, according to the degree of advancement of the demographic transition. The demographic transition is characterized by different phases.

• The emerging transition: with high birth and mortality and with moderate natural growth of 2.5 %, they have a very young age structure and a high dependency ratio.
• The moderate transition: high birth but moderate mortality. For this reason its natural growth is still high, close to 3 %. At this stage, for example, Guatemala, where the decline in mortality, especially during the first year of life, has resulted in a rejuvenation of the structure by age, which also leads to a high dependency ratio.
• The full transition: with moderate birth and moderate or low mortality, which determines moderate natural growth close to 2 %. Here the decline in fertility is recent and the age structure is still relatively young, even though the dependency ratio has already decreased.
• The advanced transition: with birth and moderate or low mortality, which results in low natural growth of 1 %.

Second demographic transition

The concept of the second demographic transition was created by Lesthaghe and D.J. van de Kaa in 1986. It is a new concept that seeks to account for emerging phenomena in developed countries, but it also seems to be confirmed in Latin American countries.

The second demographic transition, in a stable context of low fertility and mortality, describes the changes in the composition of the family and unions in the patterns of family reconstitution in Western countries.

In addition to fertility levels below the replacement level and sustained over time, the second demographic transition is characterized by: (i) increased singleness, (ii) delayed marriage, (iii) postponement of the first child, (iv) expansion of consensual unions, (v) expansion of births out of wedlock, (vi) rise in marital breakdowns, (vii) diversification of family structuring modalities.

Reproductive Revolution

The theory of the reproductive revolution is critical of the limitations of the general theory of demographic transition derived from its research methodology -supported by cross-sectional studies and expressed in population pyramids- since would project an incomplete, non-holistic vision of population dynamics (new phases must be incorporated into the demographic transition to account for new phenomena) leaving without explanation some of the reproduction mechanisms of populations in the intergenerational succession that are manifesting in societies modern. As a paradigm shift proposal, the reproductive revolution -supported by longitudinal studies- aims to account for demographic changes in a systemic and non-alarmist or catastrophic manner, largely integrating the sociological consequences that characterize the second demographic transition.

The theory of the reproductive revolution is described by John MacInnes and Julio Pérez Díaz in their publications The reproductive revolution of 2005 and 2009 The third revolution of modernity. The reproductive revolution and The reproductive revolution. The authors point out the radical relevance that the concept of reproductive efficiency has in their theory and in the new demographic phenomena, as well as longevity and Generational replacement in modern societies. Following the common thread of the ideas of Kingsley Davis (1908-1997) exposed in 1937 on the future of the family and fertility, he establishes very different consequences on the implications and consequences that the reproductive revolution has in the decrease of reproductive work: the decline of patriarchy, the social deregulation of sexuality, the transition from gender to generation as the axis of distribution of productive-reproductive roles, the strengthening of family ties and other positive consequences of mass maturity-the misnamed aging of the population-.

Variation of ages and sex

In most countries of the world the population of women is greater than that of men, although in a few countries such as Andorra, Albania, China, Costa Rica, the Philippines, India, most of the countries of the East Middle, Panama, Paraguay and the Dominican Republic among others, is estimated to have a majority male population.

However, in the case of countries where the majority are female, it is because old age is included in the estimates. Females in the elderly population are the majority worldwide. This is in accordance with the science that establishes that women enjoy more longevity than men. However, if we leave this stage aside we will find that the population of children, adolescents and adults are often the majority, for example in countries such as Germany, France, Japan, South Korea, Cuba, Belgium, Spain, Italy, UK etc In recent years, children and adolescents in the male population outnumber females, but in the young and adult population, females continue to be the majority, for example in countries such as Argentina, Bolivia, Brazil, Canada, El Salvador, the United States, the Philippines, Guatemala, Equatorial Guinea, Guinea Bissau, Peru, Portugal, Puerto Rico, Russia and some Balkan countries, among others.

In addition, it is estimated that in some countries such as Belgium, Canada, Cuba, France, Israel, Japan, Puerto Rico, some Arab countries and among others, the male population could equal or exceed the female population, since in these countries there is a frank growth.^{[citation required]}

Importance of demographics

In public health

1. Development of health rates and other indicators
2. Epidemiology studies: In epidemiological studies, population data and distribution are required according to characteristics of person, place and time.
3. Public health planning
4. Food production planning (human food)
5. General national or regional development plans
6. Properly project the public health plan

Demographic resources in Spanish-speaking countries

• Surveys
• Pads
• Civil Registry and National Statistical Institute in Spain
• In Argentina, the National Institute of Statistics and Censuses.
• In Bolivia, the National Statistical Institute.
• In Chile, the National Statistical Institute
• In Colombia, the National Administrative Department of Statistics.
• In Ecuador, the National Institute of Statistics and Censuses of Ecuador.
• In Spain, the National Statistical Institute.
• In Mexico, the National Institute of Statistics and Geography.
• In Paraguay, the Directorate-General for Statistics, Surveys and Censuses.
• In Peru, the National Institute of Statistics and Informatics.
• In Puerto Rico, the Puerto Rico Demographic Record, the Puerto Rico Statistics Institute and the Census Bureau - Puerto Rico Planning Board.
• In Uruguay, the National Institute of Statistics of Uruguay.
• In Venezuela, the National Statistical Institute of Venezuela.
• In Nicaragua, the Nicaraguan National Statistical Institute.
• In Panama, the National Institute of Statistics and Census

12. Universal encyclopedic dictionary / Universal Geography and Mexico pages 32-33 / population growth

Expression of demographic data