Population ageing is an overall change in the ages of a population. This can typically be summarised in a single parameter as an increase in the median age. Causes are a long-term decline in fertility rates and a decline in mortality rates. Most countries now have declining mortality rates and an ageing population: trends that emerged first in developed countries but are now also seen in virtually all developing countries. In most developed countries, population ageing started in the late 19th century. By the late 20th century, the world population as a whole was also ageing. The proportion of people aged 65 and above accounts for 6% of the total population. This reflects a historic overall decline in the world's average fertility rate. That is the case for every country in the world except the 18 countries designated as "demographic outliers" by the United Nations. The aged population is currently at its highest level in human history. The UN projects that the population will age faster in the 21st century than in the 20th. The number of people aged 60 years and over has tripled since 1950; it reached 600 million in 2000 and surpassed 700 million in 2006. It is projected that the combined senior and geriatric population will reach 2.1 billion by 2050. Countries vary significantly in terms of the degree and pace of ageing, and the UN expects populations that began ageing later will have less time to respond to its implications. Policy interventions include preventative strategies that increase the size of the young, working-age population, as well as adaptive measures to make overarching systems compatible with a new demographic future.
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Population aging in the context of Gerontology
Gerontology (/ˌdʒɛrənˈtɒlədʒi/ JERR-ən-TOL-ə-jee) is the study of the biological, cognitive, cultural, psychological, and social aspects of ageing. The word was coined by Ilya Ilyich Mechnikov in 1903, from the Greek γέρων (gérōn), meaning "old man", and -λογία (-logía), meaning "study of". The field is distinguished from geriatrics, which is the branch of medicine that specializes in the treatment of existing disease in older adults. Gerontologists include researchers and practitioners in the fields of biology, nursing, medicine, criminology, dentistry, social work, physical and occupational therapy, psychology, psychiatry, sociology, economics, political science, architecture, geography, pharmacy, public health, housing, and anthropology.
The multidisciplinary nature of gerontology means that there are a number of sub-fields which overlap with gerontology. There are policy issues, for example, involved in government planning and the operation of nursing homes, investigating the effects of an aging population on society, and the design of residential spaces for older people that facilitate the development of a sense of place or home. Dr. Lawton, a behavioral psychologist at the Philadelphia Geriatric Center, was among the first to recognize the need for living spaces designed to accommodate the elderly, especially those with Alzheimer's disease. As an academic discipline the field is relatively new. The USC Leonard Davis School of Gerontology created the first PhD, master's and bachelor's degree programs in gerontology in 1975.