Читать книгу Demographic Dynamics and Development - Yves Charbit - Страница 11

Demographic dynamics come down to a fundamental equation. Every year the growth or decline of a given population (P) is reduced to the interaction of four variables:

(2020 Total population) = (2019 Total population) + (2019 births) –

(2019 deaths) + (2019 immigration) – (2019 emigration)

From this, three simple definitions follow:

 – the difference between births and deaths in a year is the natural increase (natural surplus or natural deficit);

 – the difference between immigration and emigration is the net migration (which can be either positive or negative). From the point of view of demographic dynamics stricto sensu, international migrations are much less important than births and deaths;

 – the total growth rate is the sum of the two indicators (natural increase and net migration), divided by the population of the previous year. It is expressed as a percentage per year.

Before 1750, when mortality and birth rates were balanced, the world population growth rate never exceeded 0.5%. Between 1750 and the 1930s, it did not exceed 1%. It reached a maximum of 2.1% per year, on average, between 1950 and 1970, when mortality in developing countries fell sharply, without a decline in birth rates. Subsequently, more and more developing countries saw their fertility rate decline, as it did in industrialized countries with the end of the baby boom of the 1950s. The combined effect of these two developments led to a steady decline in the world population growth rate: 1.95% in 1970, 1.26% in 2000 and 1.09% in 2020.

Another aspect of demographic dynamics that is directly related to changes in flows must be mentioned. Their very accumulation determines population stocks. Thus, the rural exodus leads to changes in the distribution between urban and rural areas, which is the process of urbanization. As for the evolution of mortality and birth rates, this is translated by the population’s age–sex distribution, conventionally represented by a pyramid. After the Second World War, developing countries experienced a large annual number of births but, due to high mortality, very few people reached adulthood. This was reflected by broad-based pyramids. In these populations, although there certainly were adults, very few were elderly people. With the gradual decline in the fertility of couples, annual birth rates decreased and the proportions of children and adults rebalanced. The population became older and demographers spoke of “aging from the bottom”. In developed countries, on the other hand, where annual birth rates are lower, the age pyramid has more adults. Over the years, these fall into the category of the third age and we speak of “top-down aging”.

These relative proportions of children, adults and the elderly led to several indicators being established, which address the issue of development. It is common to draw a distinction between consumers and producers or, more precisely, to differentiate the inactive from the active. We thus calculate a dependency ratio, where the numerator includes 0–19 year olds (young people) and those aged 60 and above (the elderly), and the denominator is the working population (20–69 year olds). Globally, the dependency ratio – equal to 75 inactive people dependent on 100 working people in 1970 – decreased to 56 in 2000 and to 53 in 2020. Another analysis was recently developed. Due to the decline in fertility, the cohorts now under the age of 15 will be replaced by smaller cohorts. But, above all, they will access the economically active ages and the relationship between consumers and producers – hitherto unfavorable due to spending on health and education weighing on national budgets – will become favorable. So far, we have provided data on world population, but is this concept actually useful?