In statistics, epidemiology, marketing and demography, a cohort is a group of subjects who share a defining characteristic (typically subjects who experienced a common event in a selected time period, such as birth or graduation).
In statistics, epidemiology, marketing and demography, a cohort is a group of subjects who share a defining characteristic (typically subjects who experienced a common event in a selected time period, such as birth or graduation).
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A generation is all of the people born and living at about the same time, regarded collectively. It also is "the average period, generally considered to be about 20–30 years, during which children are born and grow up, become adults, and begin to have children." In kinship, generation is a structural term, designating the parent–child relationship. In biology, generation also means biogenesis, reproduction, and procreation.
Generation is also a synonym for birth/age cohort in demographics, marketing, and social science, where it means "people within a delineated population who experience the same significant events within a given period of time." The term generation in this sense, also known as social generations, is widely used in popular culture and is a basis of sociological analysis. Serious analysis of generations began in the nineteenth century, emerging from an increasing awareness of the possibility of permanent social change and the idea of youthful rebellion against the established social order. Some analysts believe that a generation is one of the fundamental social categories in a society; others consider generation less important than class, gender, race, and education.
Human life expectancy is a statistical measure of the estimate of the average remaining years of life at a given age. The most commonly used measure is life expectancy at birth (LEB, or in demographic notation e0, where ex denotes the average life remaining at age x). This can be defined in two ways. Cohort LEB is the mean length of life of a birth cohort (in this case, all individuals born in a given year) and can be computed only for cohorts born so long ago that all their members have died. Period LEB is the mean length of life of a hypothetical cohort assumed to be exposed, from birth through death, to the mortality rates observed at a given year. National LEB figures reported by national agencies and international organizations for human populations are estimates of period LEB.
Human remains from the early Bronze Age indicate an LEB of 24. In 2019, world LEB was 73.3. A combination of high infant mortality and deaths in young adulthood from accidents, epidemics, plagues, wars, and childbirth, before modern medicine was widely available, significantly lowers LEB. For example, a society with a LEB of 40 would have relatively few people dying at exactly 40: most will die before 30 or after 55. In populations with high infant mortality rates, LEB is highly sensitive to the rate of death in the first few years of life. Because of this sensitivity, LEB can be grossly misinterpreted, leading to the belief that a population with a low LEB would have a small proportion of older people. A different measure, such as life expectancy at age 5 (e5), can be used to exclude the effect of infant mortality to provide a simple measure of overall mortality rates other than in early childhood. For instance, in a society with a life expectancy of 30, it may nevertheless be common to have a 40-year remaining timespan at age 5 (but not a 60-year one).
Longevity may refer to especially long-lived members of a population, whereas life expectancy is defined statistically as the average number of years remaining at a given age. For example, a population's life expectancy at birth is the same as the average age at death for all people born in the same year (in the case of cohorts).
Longevity studies may involve putative methods to extend life. Longevity has been a topic not only for the scientific community but also for writers of travel, science fiction, and utopian novels. The legendary fountain of youth appeared in the work of the Ancient Greek historian Herodotus.
Future generations are cohorts of hypothetical people not yet born. Future generations are contrasted with current and past generations and evoked in order to encourage thinking about intergenerational equity. The moral patienthood of future generations has been argued for extensively among philosophers, and is thought of as an important, neglected cause by the effective altruism community. The term is often used in describing the conservation or preservation of cultural heritage or natural heritage.
The sustainability and climate movements have adopted the concept as a tool for enshrining principles of long-term thinking into law. The concept is often connected to indigenous thinking as a principle for ecological action, such as the seven generation concept attributed to Iroquois tradition.
Millennials, also known as Generation Y or Gen Y, are the demographic cohort following Generation X and preceding Generation Z. Researchers and popular media use the early 1980s as starting birth years and the mid-1990s to early 2000s as ending birth years, with the generation typically being defined as people born from 1981 to 1996. Most millennials are the children of baby boomers and older Gen Xers, and are often the parents of Generation Alpha.
As children in the late 1980s to 2000s, millennials saw the rise of the Information Age and Internet, being described by some as the first global generation. As adolescents and young adults in the late 1990s to 2010s, the generation was marked by a more upbeat youth culture, elevated familiarity with the Internet and technology in general, and usage of early social media platforms such as AOL Instant Messenger, LiveJournal, and Myspace. Between the 1990s and 2010s, people from developing countries became increasingly well-educated, a factor that boosted economic growth in these countries.
Baby boomers, often shortened to boomers, are the demographic cohort preceded by the Silent Generation and followed by Generation X. The generation is often defined as people born from 1946 to 1964 during the mid-20th-century baby boom that followed the end of World War II. The dates, the demographic context, and the cultural identifiers may vary by country. Most boomers are the parents of Generation X and Millennials.
In the West, boomers' childhoods in the 1950s and 1960s had significant reforms in education, both as part of the ideological confrontation that was the Cold War, and as a continuation of the interwar period. Theirs was a time of economic prosperity and rapid technological progress, and many grew up expecting the world to improve with time.