Glossary of Demographic Terms

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The aim of this glossary is to help you grasp terminology and terms related to the board field of demographic change. The Rostock Center does not claim to provide a complete glossary on demography; it rather aims to briefly explain the technical terms used in scientific articles to be understood by everyone, ranging from pupils to the very old. You can browse the glossary here.




A term derived from English to denote discrimination on grounds of age (comparable to racism, sexism) 


Baby boom cohorts

Birth cohorts born during the so-called Baby Boom (in West Germany a period covering approx. the mid-1950s to mid-1960s). These years, marked by economic and social recovery following World War II, witnessed higher birth rates and an increase in the absolute number of births. Baby boom cohorts thus are disproportionally large in number compared to other birth cohorts.

Birth cohort

All people born during a specific calendar year or time period.

Also see: Cohort

Birth deficit

A region has a birth deficit, when the number of live births is lower than the number of deaths within a defined period of time.

Birth rate

Also: Total fertility rate

The cruder (i.e., general) birth rate is the number of live births per 1000 inhabitants in a year (8.4 for Germany in 2012). The crude birth rate is determined not only by the fertility of a given population but also by its age structure. Age-specific birth rates are calculated separately by age for women at childbearing ages. An example is the number of children born alive to 30-year-old women in one year based on 1000 women aged 30. In everyday language, the birth rate is often mistaken for the total fertility rate.   

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People aged 100 or over called Centenarians (lit.:  hundreds).

See also: Semi-Supercentenarians and Supercentenarians


Designates a group of people who have a time-related characteristic in common. A birth cohort comprises, for example, all people born in a given year (generally limited by further criteria, e.g., the country of birth). But the year of marriage or immigration may also be of demographic relevance, for example.

Cohort fertility

Cohort fertility (in contrast to period fertility) is the number of live births per woman who were born in a particular year (= cohort). This measure is less susceptible to fluctuations than is period fertility. The measure can only be determined in retrospect, however, i.e., once the reproductive phase of the given cohort has ended.

Cohort mortality

The mortality of a given birth cohort observed over time. Cohort mortality is used to track the development of mortality in a given birth cohort.

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Research discipline investigating the structure and dynamics of populations. The size and structure of populations change as people are born, die, or move (demographic components: fertility, mortality, migration and, in a broader sense: morbidity and nuptiality).

Demographic change

Demographic change describes the changes in population size and structure caused by changes in birth rates, death rates, and by migration. Demographic change in the Western developed countries of today is marked by low birth rates below population replacement and by rising life expectancy. The result is that populations are aging and shrinking. And migration may overlap with these developments. Migration, for example, leads to further population reductions in the regions of origin and to attenuation in the regions of destination. And if it is the young rather than the old who migrate from a region, aging is exacerbated in the region of origin.

Demographic change has always exited, if seen purely as a process of population development. But the extent of demographic change we see today will necessitate drastic adjustments in many areas of society and politics.

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Earning points

The pension payment to which a person is entitled under the statutory pension scheme is based primarily on earnings accrued during working life. The calculation of pension entitlement includes gross earnings per year. These are then converted into earning points. To do so, the annual income is set in relation to the average annual income of all contributors to the pension fund. If the income equals that average, the result is an earning point of 1 for that year. This way, a total sum of 45 earning points would be accrued after 45 years of employment (up to age 65). For earnings higher (or lower) than the average annual income, earning point values increase (or decreases) accordingly above (or below) 1.

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Fetal Origins Hypothesis

Posits that the predisposition to certain chronic diseases (and thus an important factor influencing individual life expectancy) is acquired as early as in utero. Possible causes for a higher risk of dying are malnutrition and infectious diseases of the mother.


General fertility of a person, couple, group, or a population, i.e., the ability to produce offspring. Fertility determines the development of population numbers and does so together with mortality and migration. The most common measure of fertility is the birth rate, reflected in the total fertility rate. If this rate is below the so-called population replacement level, the population is shrinking.

See also: cohort fertility and period fertility


Prediction about a future event, condition, or development. A forecast is always based on assumptions that need to be made (e.g., about fertility, mortality, and migration when predicting how the population structure will develop over the next 30 years). Forecasts are always subject to a certain degree of inaccuracy. This is because the assumptions made are about the future and unforeseen developments may occur, especially when forecasts are long term.

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Generation renewal

This means that the number of deaths in a population is offset in the long run by the number of births, so that the population number in that region remains constant.

See also: Replacement level

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Healthy Migrant Hypothesis

The hypothesis posits that the health of migrants is better on average, thus they  have a higher life expectancy.

Human Development Index

The Human Development Index (HDI) measures the average socio-economic development of a country by taking into account three basic factors:  the health, the education, and the living standard in a population. To this end, three indices are constructed preceding HDI calculations: (1) Health – A country's health status is measured by using life expectancy at birth. (2) Education – The index of a country's educational attainment is generated from the rate of adult literacy and the combined school-enrolment rate at primary, secondary, and tertiary levels of education. (3) Standard of living – The index of living standard is based on real purchasing power per capita in US dollars. The United Nations Development Programme (UNDP) has been publishing HDIs since 1990 in its Human Development Reports. For more information on the concept of the Human Development Index, see the UNDP website. 

Human Mortality Database

The Human Mortality Database is a free database accessible to all who are interested. The data document the development of longevity over the past decades for 37 countries and regions. Its purpose is to intensify and facilitate research into the causes and consequences of mortality. The main goals are to ensure comparability, flexibility, and free global access to the data.

Launched in 2002 by researchers from the Department of Demography at the University of California, USA, and the MPIDR's Data Laboratory, the database provides the following data on all countries and regions listed below, based on uniform methods to calculate life tables:

1) Absolute counts of life births (by sex)

2) Absolute counts of deaths (by age, year of death, and year of birth)

3) Population size

4) Figures on populations exposed to the risk of death (for periods and cohorts)

5) Death rates (for periods and cohorts)

6) Life tables (for periods)

Currently (2019), data for the following 41 countries are available:

For further information, see

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In medicine, incidence is the number of new cases of a specific disease arising in a given population during a defined period of time.

See also: Prevalence

Incidence rate

The incidence rate is calculated by setting the number of new cases of a specific disease (counter) in relation to a defined population at risk (denominator), usually based on one calendar year and 1000 persons.

See also: Prevalence rate

Infant mortality

This indicator measures how many of 1000 infants born alive die in a given calendar year before reaching their first birthday. According to the Federal Statistical Office, the current infant mortality rate for Germany is 3.3.

Internal migration

Migration within national borders.

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Life expectancy

(= period life expectancy)

A measure to standardize the mortality rates of one calendar year or several calendar years (i.e., period). Life expectancy shows the average number of years a person of a given age can expect to live, assuming that age-specific mortality rates remain constant for the rest of that person’s life. A distinction is made between life expectancy at birth and remaining life expectancy (i.e., the years a person can expect to live at a given age).

Life Table

(= mortality table)

A tabular display of the mortality for a predefined initial population. The table shows how many people are still alive or have died by the end of age 1, 2, 3 and so forth. The most important values of life tables are calculated on the basis of age-specific survival and mortality probabilities. Life tables are used, for example, to calculate insurance premiums, such as for life, private pension, or health insurances.

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In statistics, the median (also: central value) is a value at the midpoint of a series of values arranged by value size. This means that 50 % of the values are below and the other 50 % are above the median value. If there is an even number of values, the median is calculated by averaging the two values in the middle of the series. An advantage of the median over the arithmetic average is that it is immune to “outliers”. To give an example: In a series of 10 people with 9 people aged 5 and one aged 80,  the average age would be 12.5; the median age, by contrast, would be 5 years.


A representative household survey of the Federal Statistical Office and the Statistical Offices of the German Länder, in which 1% of all households in Germany are annually involved.  Each household is selected at random using certain criteria and surveyed over a period of four years. The Microcensus has been conducted since 1957 and provides statistical information on the economic and social situation of the population, on employment, the labor market, and education.


Movement of individuals who leave their region of residence to live in another region.


Indicator of a population's state of health. It refers to the incidence and frequency of diseases and disabilities in a group (e.g., the total population, a birth cohort, or a generation).


(= death)

Mortality is influenced by biological, medical, and socio-economic determinants and by individual lifestyle factors. One of the instruments to measures mortality is the mortality rate.

Mortality rate

The number of deaths per 1000 individuals within a specified population and a specified period of time (usually one year). 

A indicator of mortality.

Mortality risk

Commonly used as a synonym for the probability of death.

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Net migration

(=  migration balance)

The difference between the number of people who enter a region (immigrants) to live there and the number of people who leave a region (migrants) to settle somewhere else.


= (age-specific) first-marriage rate

Shows the share of people who married for the first time ever at a given age for the year observed.


NUTS (French: Nomenclature des unités territoriales statistiques) is a geocode standard for referencing the regions of the European Union. To enable comparability between geospatial areas and statistical data, the regions are divided into separate entities and classified in hierarchical order, based on existing administrative units and populations of similar size.

NUTS Level 0: nation states

NUTS Level 1: larger regions / areas of a country

NUTS Level 2: basic regions / areas of a country

NUTS Level 3: small regions / large cities of a country Example for DE803

NUTS Level 0: DE for Germany

NUTS Level 1: DE8 for Mecklenburg-Western Pomerania (MVP)

NUTS Level 2: DE80 for Mecklenburg-Western Pomerania (no further subdivision at this level)

NUTS Level 3: DE803 for the County Borough of Rostock

The NUTS classification is used, for example, for socio-economic analyses of regions and when provision of financial subsidies is made by European Union structural funds.

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Old-age dependency ratio

An indicator of the ratio of pensioners to the working population. The old-age dependency ratio is calculated as the number of persons aged over 60 (or: 65 or 67) divided by the number of persons aged 20-59 (or: 64 or 66). In Germany of 2013, the old-age dependency ratio (65 years) was 34. According to the projections of the Federal Statistical Office, this will have risen significantly by 2060.

Opportunity costs

A common concept in economic research. It is the loss of a potential gain when a decision is made for one alternative against another.

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Peer group

Generally, this is any group of individuals who have similar social characteristics and share the same values and norms. The term commonly refers to age groups and in particular to that of adolescents and their culture, marked by a high degree of cohesion, by hierarchical organization, and a negative attitude toward the culture of the parents.

Period fertility

See: Total fertility rate

Period life expectancy

See: Life expectancy

Plasticity of longevity

(= plasticity of mortality)

Generally, the ability of being shaped. Here: Changes in lifespan. This hypothesis posits that the likelihood of dying can be reduced even at very old ages, i.e., remaining life expectancy can be prolonged.

Population momentum

Sustained population growth that is relatively strong – even if the birth rate per woman falls below replacement – due to the high proportion of young people at childbearing ages in the population. The population momentum explains, among other things, why population growth in developing countries (i.e., countries with a very young age structure compared to industrialized countries) is still unbroken despite declining birth rates. 

Population pyramid

Graphical illustration of a population’s age structure in a coordinate system in which are plotted on the X-axis the amount of men (mostly on the left) and women (mostly on the right) of the various age groups (Y-axis). In traditional societies with a high birth rate, the age pyramid has a broad base of younger people and the higher age groups have increasingly fewer people. If the birth rate falls – as has been observed for most developed countries in recent decades – and remains below the mortality rate, the pyramid changes in the long run to take the shape of an urn (fewer young people at the base and a broad middle layer).


In medicine, prevalence is the statistical frequency of a disease in a population at a given point in time.

See also: Incidence

Prevalence rate

The prevalence rate is derived from the ratio between the number of people affected by a condition, incidence, or development in a population and the total population. A prevalence that refers to a specific time period is called period prevalence. *

See also: Incidence rate

Probabilistic forecasts

Forecasts that show a probability distribution of future events or other future. Good probabilistic forecasts consider all uncertainties that are likely (e.g., future directions that a given variable used in the forecast may take). 

Probability of dying

(= usually used as a synonym for mortality risk)

The probability of a person who has attained a given age to die before reaching the next age. The probability of dying at age x is defined as the number of deaths at age x divided by the number of people alive at the beginning of age x, i.e., all people who reach the exact age of x and are now at risk of dying  before they reach age x+1. The probability of dying increases with age, starting from late childhood.  The odds of dying for different age groups are usually derived from age-specific mortality rates, and they are the basis for life table calculations


(= promoting birth)

The term is commonly used in the context of pronatalist family policy (which is geared toward increasing a country’s birth rate).

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Record life-expectancy

The highest life expectancy in the world observed in a given year. The record is currently held by Japanese women, with a life expectancy of 85 years.

Replacement level

Also: Simple replacement level.

The population replacement level is the average number of children per woman (total fertility rate) that would be needed to keep the population constant at the given mortality rates. For Europe, this is currently 2.1 (a rough guide). That is, if 1000 women belonging to a cohort have fewer than 2100 children over their lifetime, in the long run the number of births no longer makes up for the number of deaths, and the population shrinks. This has been applying to Germany since the 1970s.

Report on the Elderly

Since 1993, the Federal Government of Germany has been issuing a report on the elderly each legislative period. The reports provide comprehensive information on the overall situation of the older population in Germany and in alternate on current main issues. To this end, the Federal Government appoints independent honorary expert commissions, which then prepare the reports; a task taking around two years of work. The commission is assisted by the written expertise of other scientists.

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Selection bias

(= sampling error, sampling effect)

In many scientific studies, there is the risk that the method of selecting test participants or the test procedure in itself distorts or influences the results. Examples are familiarization and habituation effects for test persons who participate in long-term studies.


The term denotes people aged 105-109

See also: Centenarians and Supercentenarians

Socio-Economic Panel (SOEP)

A German longitudinal survey that started in 1984 and is followed up annually. It surveys Germans, foreigners and migrants living in the new and the old Länder. Main topics covered are employment and family biography, participation in the labor market and job mobility, income trajectories, health, and life satisfaction, next to others.

Spouse splitting

Procedure to calculate the income tax of married couples who are jointly assessed for tax purposes. To determine the total tax to be paid, the taxable income of both spouses is added and then divided by 2 (“splitted”). The tax is then calculated for this amount and doubled again. This method provides for a tax-free allowance to be factored in for both spouses and for the tax rate (in progressive tax systems) to rise more slowly when income grows. Spouse splitting is particularly advantageous when income differences between both spouses are very large.


A term to denote people aged 110 or  over.

See also: Centenarians and Semi-Supercentenarians

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Tempo effect

Commonly associated with the total fertility rate (period fertility, TFR). Tempo effects generally are distortions in period measures caused by changes in the timing of demographic events (e.g., births, deaths).  With fertility, increases in the average age at childbearing result in shifts of childbearing to later stages in life, inevitably producing underestimations of fertility levels , e.g., as measured by the TFR. In the demographic literature, various formulae have been proposed to correct for tempo distortions.


See also: Total Fertility Rate

+Total Fertility Rate (TFR)

See also: period fertility

This is the average number of children a women would have over the course of her life if she were to pass through her childbearing years conforming to the age-specific fertility rates observed for a given year.

Cf.  cohort fertility

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Working population

All persons of working age; employed are those actively engaged in paid employment. The labor-force participation rate is the share of the labor force to the total population.

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The Max Planck Institute for Demographic Research (MPIDR) in Rostock is one of the leading demographic research centers in the world. It's part of the Max Planck Society, the internationally renowned German research society.