Population studies is broadly defined as the scientific study of human populations. Major areas studied include broad population dynamics; fertility and family dynamics; health, aging, and mortality; and human capital and labor markets. Researchers in population studies also focus on methodology. Population studies is an interdisciplinary area of study; scholars from demography, epidemiology, sociology, economics, anthropology, and various other disciplines study populations. Various associations and centers exist throughout the United States and elsewhere. The Population Association of America, established in 1930, is a scientific, professional organization established to promote the improvement, advancement, and progress through research of problems related to human populations. Many university-based population studies centers are located throughout the United States, such as the University of Michigan’s Population Studies Center and the University of North Carolina at Chapel Hill’s Carolina Population Center.
Among population researchers, demographers are concerned with the empirical study of population dynamics; that is, demographers study population determinants and consequences including size, composition, how populations change over time, and the processes influencing those changes. Demographers deal with the collection, presentation, and analysis of data relating to the basic life-cycle events and experiences of people: birth, marriage, divorce, household and family formation, migration, employment, aging, and death. They also examine compositions of populations by sex, age, race, ethnicity, occupation, education, religion, marital status, and living arrangements. Demographers further assess the distribution of populations by region, country, province or state, urban or rural area, and by neighborhood. Most demographic data come from population censuses, vital registration systems, national registers, and surveys.
Demographers use a variety of counts, rates, ratios, and other statistics to measure fertility, mortality, migration, and other population dynamics. The crude birth rate is the annual number of live births per thousand people; the general fertility rate is the annual number of live births per thousand women of childbearing age. The crude death rate is the total number of deaths per thousand people; the mortality rate is the number of deaths in some population, scaled to the size of that population, per unit of time. The morbidity rate refers to the number of people who have a disease compared to the total number of people in a population. The infant mortality rate is the annual number of deaths of children less than one year old per thousand live births. Life expectancy is defined as the number of years that an individual at a given age can expect to live at present mortality levels. For example, in 2001 the average life expectancy at birth in the United States was seventy-seven years.
The crude death rate, applied to a whole population, can be misleading. For example, the number of deaths per thousand people can be higher for developed nations than for less-developed countries, despite standards of health being better in developed countries. This is because developed countries have relatively older people, who are more likely to die in a given year, so that the overall mortality rate can be higher even if the mortality rate at any given age is lower. A more complete picture of mortality and life expectancy is given by a life table that summarizes mortality separately at each age. A life table is a table that shows, for a given person at a given age, what the probability is that the person dies before his or her next birthday. Life tables are usually constructed separately for men and for women because of their different mortality rates. Other characteristics can also be used to distinguish different risks, such as health behaviors and socioeconomic position.
As the world population doubled from three to six billion, researchers in population studies have been examining shifts in population dynamics. The first five years of the twenty-first century saw a decline in the overall volume of population growth, with the world’s population increasing at a rate of about seventy-six million people per year as of 2005. Overpopulation occurs when the population of a living species exceeds the carrying capacity of its ecological niche. At the end of the eighteenth century, economist Thomas Malthus (1766–1834) concluded that, if unchecked, populations would be subject to exponential growth. He feared that population growth would surpass growth in food production, leading to ever increasing famine and poverty. On a global scale, however, food production has grown faster than population. Moreover, contrary to Malthus’s predictions, natural population growth in most developed countries has diminished to close to zero, without being held in check by famine or lack of resources. This pattern of population growth, with slow (or no) growth in preindustrial societies, followed by fast growth as the society develops and industrializes, followed by slow growth again as it becomes more affluent, is known as a demographic transition Benjamin Gompertz’s (1779–1865) law of mortality, a demographic model published in 1825, is a refinement of Malthus’s demographic model.
Future population growth is difficult to predict. Birth rates are declining on average, but vary greatly between developed countries (where birth rates are often at or below replacement levels) and developing countries. Death rates can change unexpectedly due to disease, wars and catastrophes, or advances in medicine. Population pyramids, graphs that display a population’s age and sex composition, are often used to provide information about future population growth or decline.
Researchers in population studies are also interested in the impact of migration on population dynamics. Migration is the geographic movement of people across a specified boundary. For instance, in the United States, suburban areas are growing more rapidly than central cities. Immigration refers to moves between countries. Immigration is one of the defining characteristics of twentieth-century America; one of the most important changes for the U.S. Census 2000 was the revision of the questions on race and Hispanic origin to better reflect the country’s growing diversity.
Population researchers are interested in various facets of family dynamics, cohabitation, marriage, childbearing, and divorce, trends in these dynamics, and differentials in fertility and family dynamics by race, ethnicity, education, and income. Fertility, the number of births for an individual or population, is distinguished from fecundity, the physiological ability of individuals or couples to have children. While the theoretical maximum is estimated to be about fifteen children per woman, even in the world’s highest fertility countries the average has rarely exceeded eight. The average fertility rate for the United States in 2003 was 2.0, and the average for the world was 2.8.
Demographers are interested in how various factors influence the probability that a woman bears a child; Kingsley Davis (1908–1997) and Judith Blake (1926–1993) in the 1950s and John Bongaarts in the 1980s identified “proximate determinates of fertility.” The primary trends of the second demographic transition include delays in fertility and marriage; increases in cohabitation, divorce, and nonmarital childbearing; and increases in maternal employment. Women also vary considerably in when and how many children they will have depending upon age, race, income, religion, and many other social, economic, and cultural factors.
Epidemiologists, population researchers who study the distribution and determinants of disease frequency, aim to identify factors that promote health and reduce the burden of disease in human populations. A disease is broadly defined as an abnormal condition of the body or mind that causes discomfort, dysfunction, or distress to the afflicted person. Some diseases are infectious, such as influenza, and can be transmitted by a variety of mechanisms. Other diseases, such as cancer and heart disease, are noninfectious or chronic. Aging is generally characterized by the declining ability to respond to stress, increasing homeostatic imbalance, and increased risk of disease. Death is the ultimate consequence of aging. Key areas of research in aging include: demographic trends; health, disease, and disability; labor force participation and retirement; and family status.
Health researchers employ a range of study designs, often integrating molecular, cellular, medical, and social levels, with the purpose of revealing unbiased relationships between exposures such as nutrition and stress or social factors such as education to outcomes like disease, well-being, and other health indicators. Morbidity and mortality rates vary by common social categories such as age, sex, socioeconomic status, and race/ethnicity. Research on social class differentials in mortality has a long history. Higher-status individuals live healthier and longer lives than their lower-status counterparts in virtually every society. Despite improvements in public health in the last halfcentury, large disparities continue to persist between and within countries for a range of health indicators.
Sociologists and economists in the field of population studies often examine labor markets and human capital such as education and skills. Researchers examine trends and inequalities in educational attainment. Other areas of study include labor force participation rates, how labor markets operate (including the matching of employees to jobs and differences across labor market segments), earnings differences, mobility, and inequalities by various demographic characteristics. Researchers also examine labor market trends, such as unemployment rates, as well as trends in length of employment relationships. There is a large amount of research on sex, race, and socioeconomic disparities in human capital and labor markets.
SEE ALSO Anthropology; Demography; Economics; Family Functioning; Family Structure; Fertility, Human; Geography; Marriage; Migration; Morbidity and Mortality; Population Control; Population Growth; Sociology
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Jennie E. Brand