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Population distribution by age and sex for Angola in 2005. A population pyramid (age structure diagram) or "age-sex pyramid" is a graphical illustration of the distribution of a population (typically that of a country or region of the world) by age groups and sex; it typically takes the shape of a pyramid when the population is growing. [1]
The Leslie matrix is a discrete, age-structured model of population growth that is very popular in population ecology named after Patrick H. Leslie. [1] [2] The Leslie matrix (also called the Leslie model) is one of the most well-known ways to describe the growth of populations (and their projected age distribution), in which a population is closed to migration, growing in an unlimited ...
An example of using age class structure to learn about a population is a regular bell curve for the population of 1-5 year-old fish with a very low population for the 3-year-olds. An age class structure with gaps in population size like the one described earlier implies a bad spawning year 3 years ago in that species. [7]
Over the age of 65: elderly, senior citizens. The age structure of a country has a strong impact on society and the economy. If the proportion of 0–14-year-olds is very high, there may be a so-called youth bulge. If, on the other hand, the proportion of over 65 is very high, the social systems of a country can be heavily burdened.
Under federal law, the Immigration and Nationality Act of 1965, [41] the number of first-generation immigrants living in the United States has increased, [42] from 9.6 million in 1970 to about 38 million in 2007. [43] Around a million people legally immigrated to the United States per year in the 1990s, up from 250,000 per year in the 1950s. [44]
The United States also has one of the highest proportions of people who do marry by age 40; approximately 85% Americans are married at 40, compared to only 60% in Sweden. During the 1930s, the number of marriages and the marriage rate dropped steeply due to the Great Depression, but rebounded almost immediately after the Depression ended.
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Population structure may refer to many aspectsof population ecology: Population structure (genetics) , also called population stratification Population pyramid