Demographics and Social Change (AAMC 9B)
Content category 9B covers who makes up a society and how that population changes. The social structure and demographics page lists the stages of the demographic transition in brief. This page explains the demographic variables sociologists use (and why several are social constructs), the rates behind population change with worked calculations, how to read a population pyramid, and the theories of social movements, globalization and urbanization. Passages in this area often present a table or graph, so practice reading the numbers.
Demographic Structure
Demography is the statistical study of human populations: their size, composition and distribution, and the processes (births, deaths, migration) that change them. The MCAT outline names several demographic variables.
- Age
- A population's age structure affects its needs. An aging population raises demand for chronic care and pensions. Ageism is prejudice or discrimination based on age.
- Gender
- Distinct from biological sex; sex ratios at birth are about 105 males per 100 females, but women live longer on average in most countries, so older age groups are majority female.
- Race
- A socially constructed category based on perceived physical differences. Racial categories change over time and differ between societies, which shows they are social rather than biological classifications. Racialization is the process of assigning racial meaning to a group; racial formation describes how such categories are created and transformed by social and political forces.
- Ethnicity
- A shared cultural heritage: language, ancestry, religion, traditions. Ethnicity is more often chosen or emphasized by the group itself; symbolic ethnicity describes ethnic identity expressed occasionally (holidays, food) without strongly shaping daily life.
- Immigration status
- Whether a person is native-born, a naturalized citizen, a legal resident, a refugee or undocumented. Status affects access to employment, services and health care.
- Sexual orientation
- Measured through self-identification, attraction or behavior, which can give different counts; a reminder that how a variable is operationalized changes the results.
The dependency ratio compares the number of people who are typically not working (children and older adults) with the working-age population. A high ratio means fewer workers support more dependents.
Age, period and cohort effects
| Effect | Meaning | Example |
|---|---|---|
| Age effect | Changes that come with getting older, whenever a person was born | Risk of hypertension rising with age |
| Period effect | Changes that affect everyone at a particular time | A recession raising stress across all ages |
| Cohort effect | Differences between groups born at different times, due to shared formative experiences | People who grew up before the internet using technology differently |
Fertility, Mortality and Migration
Population change comes from three processes: births, deaths and migration.
- Crude birth rate
- Births per 1,000 people per year.
- Total fertility rate (TFR)
- The average number of children a woman would have over her lifetime at current age-specific birth rates. Replacement-level fertility is about 2.1 in countries with low mortality (slightly above 2 because some children die before reproducing and slightly more boys than girls are born).
- Crude death rate
- Deaths per 1,000 people per year. It can be misleading when comparing populations of different age structures, so researchers use age-adjusted rates.
- Infant mortality rate
- Deaths of infants under 1 year per 1,000 live births; a sensitive indicator of a population's health and health care access.
- Life expectancy
- The average number of years a newborn would live at current mortality rates.
- Migration
- Immigration (moving in) and emigration (moving out). Push factors drive people away (war, poverty, persecution, environmental disaster); pull factors attract them (jobs, safety, family). Migration can be internal (within a country) or international.
A city of 200,000 people records 3,000 births, 1,600 deaths, 1,400 immigrants and 800 emigrants in a year.
Crude birth rate = 3,000 / 200,000 × 1,000 = 15 per 1,000. Crude death rate = 1,600 / 200,000 × 1,000 = 8 per 1,000. Natural increase = 15 − 8 = 7 per 1,000. Net migration = (1,400 − 800) / 200,000 × 1,000 = 3 per 1,000. Total growth = 10 per 1,000 = 1.0% per year.
A useful shortcut: dividing 70 by the annual growth rate (in percent) gives the approximate doubling time, so this city would double in about 70 years if growth stayed constant.
Population Pyramids and the Demographic Transition
A population pyramid is a pair of horizontal bar graphs showing the number or percentage of males and females in each age group.
| Shape | What it indicates | Typical setting |
|---|---|---|
| Expansive (wide base, narrow top) | High birth rate, high death rate, rapid growth, young population | Countries early in the demographic transition |
| Stationary (roughly column-shaped) | Low birth and death rates, little growth | Countries late in the transition |
| Constrictive (narrower base than middle) | Birth rate below replacement, aging and possibly shrinking population | Some high-income countries |
The demographic transition describes how populations move from high birth and death rates to low birth and death rates as they industrialize. Death rates fall first (better food, sanitation and medicine), producing rapid growth, and birth rates fall later (urbanization, education of women, contraception, and children shifting from economic assets to costs). The theory is based mainly on European history and does not fit every society's path.
Thomas Malthus argued that population grows geometrically while food supply grows arithmetically, so population would outstrip food until checked by famine, disease or war. Agricultural productivity has so far outpaced his prediction, but his ideas still frame debates about resources and sustainability.
Fertility, mortality and migration interact with social structure: an aging population shifts political priorities toward pensions and health care, while immigration can offset low fertility and change a society's ethnic composition.
Social Movements
A social movement is an organized, sustained effort by a group to promote or resist social change. Proactive movements promote change; reactive movements resist it.
| Type | Scope of change | Target |
|---|---|---|
| Alternative | Limited | Specific individuals (encouraging people to stop a particular behavior) |
| Redemptive | Radical | Specific individuals (religious conversion) |
| Reformative | Limited | Society (changing a specific law or policy) |
| Revolutionary | Radical | Society (replacing the existing system) |
- Relative deprivation theory
- Movements arise when people feel deprived relative to what they expect or to a comparison group, not necessarily when they are absolutely poorest.
- Resource mobilization theory
- Discontent is always present; movements succeed when they can mobilize resources such as money, members, leaders, organization and media access.
- Political process theory
- Movements succeed when political opportunities open up, such as divisions among elites or sympathetic allies in government.
- New social movements
- Post-industrial movements focused on identity, quality of life and values (environmental, human rights) rather than economic class.
Movements often follow a life cycle: emergence (discontent spreads), coalescence (organization and strategy form), bureaucratization (formal structure and paid staff), and decline (through success, co-optation, repression or loss of support).
Globalization
Globalization is the growing integration of economies, cultures and populations across the world, driven by trade, communication technology, transportation and migration. It can spread wealth, ideas and medical advances, and it can also spread disease quickly, displace local industries and increase inequality within and between nations.
| Theory | Claim |
|---|---|
| Modernization theory | Poorer nations will develop by adopting the technology, institutions and values of industrialized nations |
| Dependency theory | Poorer nations are kept poor by economic dependence on wealthy nations that extract their resources and labor |
| World systems theory (Wallerstein) | The world economy is divided into core nations (wealthy, industrialized), periphery nations (supply raw materials and cheap labor), and semi-periphery nations in between; position in this system shapes development |
Urbanization
Urbanization is the growth of the proportion of a population living in cities. It accelerated with industrialization, as jobs concentrated in factories and services; today more than half of the world's population is urban.
- Suburbanization
- Movement of population from city centers to surrounding suburbs, often enabled by cars and highways; historically associated with middle-class and white flight from cities and with a declining urban tax base.
- Gentrification
- Higher-income residents move into a lower-income urban neighborhood, raising property values and rents; brings investment but often displaces long-time residents.
- Urban renewal
- Redevelopment of urban areas, sometimes through demolition, which can also displace communities.
- Urban decline
- Loss of population, jobs and services in a city area, concentrating poverty.
Where people live shapes their access to jobs, schools, healthy food and health care, which links urbanization to spatial inequality.
Worked MCQs
5 MCQs in the style of the Psych/Soc section, several built around a study design.
Q1. A country's population pyramid has a narrow base, a wide middle and a relatively wide top. Which conclusion is best supported?
A narrow base relative to the middle (a constrictive pyramid) indicates that recent birth cohorts are smaller than earlier ones, consistent with below-replacement fertility and an aging population.
Q2. A town of 50,000 has 600 births and 400 deaths in a year, with no migration. Its rate of natural increase is:
Crude birth rate = 600 / 50,000 x 1,000 = 12 per 1,000. Crude death rate = 400 / 50,000 x 1,000 = 8 per 1,000. Natural increase = 12 - 8 = 4 per 1,000, or 0.4% per year.
Q3. Survey data show that adults born in the 1990s report more comfort with telehealth than adults born in the 1950s, and the difference persists across all survey years from 2015 to 2025. This difference is best described as:
A stable difference between groups born in different eras, persisting over time, reflects shared formative experiences of each birth cohort, which is a cohort effect. A period effect would shift all groups at the same time.
Q4. According to world systems theory, a nation whose economy depends mainly on exporting raw materials to wealthy industrialized nations is part of the:
World systems theory places nations that supply raw materials and cheap labor to the industrialized core in the periphery. Semi-periphery nations have intermediate levels of industrialization.
Q5. A movement grows rapidly after it gains a large donor base, trained organizers and access to national media, although public discontent with the issue had been steady for decades. This is best explained by:
Resource mobilization theory holds that discontent alone does not create movements; success depends on mobilizing resources such as money, organization, leadership and media access. The steady level of discontent argues against relative deprivation as the trigger.
Quick Recap
- Demographic variables: age, gender, race (socially constructed), ethnicity, immigration status, sexual orientation.
- Age vs period vs cohort effects; cross-sectional studies confound age and cohort.
- Crude birth and death rates are per 1,000 per year; TFR replacement is about 2.1; infant mortality per 1,000 live births.
- Growth = (births - deaths + net migration) / population; rule of 70 for doubling time.
- Pyramids: expansive (young, growing), stationary, constrictive (aging, below replacement).
- Demographic transition: death rates fall first, then birth rates. Malthus: population outstrips food.
- Movements: alternative, redemptive, reformative, revolutionary; relative deprivation vs resource mobilization.
- Globalization: modernization, dependency, world systems (core, semi-periphery, periphery). Urbanization: suburbanization, gentrification.