The United Nations Expert Group states world population has increased from 1.6 billion to 6.1 billion over the course of the 20th century (Urdal, 2008). However, the previous century has challenged population patterns not only quantitatively but also qualitatively. New economical and political realities anticipate novel methodological approaches to assess social structure. Recent statistical achievements and monitoring instruments reveal specific trends in the world societies to deal with.
An increasing society is expected to have more children in its demographic structure. This is contrary to a decreasing society that will have fewer children, while a steady population is balanced. Thus, by examining the proportions of different age groups within a population allows to appreciate the estimated and projected changes (UN Department of Economic and Social Affairs, 2004). The so-called population pyramids depict demographic structures in the more or less developed countries.
The United Nations (UN Department of Economic and Social Affairs, 2004) report emphasizes:
The age composition of a population is important for several reasons. The proportions of children and older persons have much to do with the balance of national expenditures on schools, childcare, immunization and reproductive health, as against expenditures on old-age social security systems and health care for chronic and degenerative disease. The ratio of the population aged 65 and over to the working-age population is a fundamental consideration in the design of public pension arrangements, and the ratio has its microlevel expression in the age structure of the family, affecting the possibilities for private care of children and older persons.
This means that should the proportion of the elderly increase, the economical load on the working population increases too, since pensions, health care programs and other social services must be paid for with increasing taxes, or services costs. On the other hand, in a society with a large proportion of children the income is expected to be spent on childcare at the expense of decreased investments into industry.
As soon as different population groups behave differently, different population compositions have different impact on the environment (Hunter, 2000). For example, today the young people dominate in the global population. This cohort is prone to migration aiming to improve economical status or opportunities. As a result, a greater level of urbanization is expected, thus challenging urban environmental patterns.