Age is time lived since birth. Demographers calculate age in a number of ways:
A. Age in completed years: age at last birthday, i.e. number of complete years lived by an individual at a given moment in time.
B. Age reached: difference between the current year and the year of birth. It is used to define a birth cohort.
C. Exact age: the exact period of time elapsed since birth and a measure that therefore increases continuously. It is expressed in years, months and days, or in tenths or hundredths of a year.
The age pyramid is a graphical representation of the age structure and sex structure of a population in a system of coordinates. While the x-axis represents the amount of men (usually on the left) and the amount of women (usually on the right), the y-axis represents the various age groups.
The age structure indicates the composition of a population by age groups, also known as age composition, or age distribution.
The age-specific death rate is the number of deaths in a certain year in a certain age group, per capita of the population in that age group. Because there are important mortality differences between males and females, age-specific mortality rates are always calculated by sex. Differences in the age composition of populations are eliminated when using age-specific death rates.
Age-specific fertility rate
The age-specific fertility rate denotes the number of live births per woman in a certain age group, per year. Differences in the age composition of populations are eliminated when using age-specific fertility rates.
The average or mean can be calculated in a number of ways:
A. The arithmetic average / mean consists of the sum of a series of quantities divided by the number of quantities. When the term average or mean is used without further qualification, the arithmetic average is generally meant.
B. The geometric average/ mean is sometimes used when all observed values are positive. It is the Nth root of the product of N values.
A baby boom is a sudden and large increase in the birth rate.
Biases are systematic errors, e.g. introduced by the sampling strategy or interviewers when data are collected. Biases can cause observation errors in demographic research and affect estimates.
The birth order describes the chronological order of live births for a woman or a couple. The first-order birth refers to the eldest child in a family. Depending on the statistics available, birth order may refer to all births to a mother or only to the births of the current marriage.
Population censuses are taken to obtain information about the state of the population at a given time. In a general census, all inhabitants of a particular country are counted simultaneously. In a partial census, only a section of the population is counted, e.g. the inhabitants of a given area. A micro census is limited to a sample of the population, usually large in size, and belongs in the category of sample surveys.
Citizenship is the status of a legal member of a sovereign state.
Cohabitation is the situation of people who share the same dwelling. As a simplification, the term cohabitants is often used to describe couples who live together without being married, and such unions are referred to as consensual unions.
A cohort is a group of persons who share a common characteristic or experience within a defined period of time. Thus a birth cohort is formed by a group of people who were born on a day or in a particular year or period. A marriage cohort is a group of persons married within a defined period. The primary objective of cohort analysis is the study of the intensity and tempo or timing of demographic phenomena in a specified cohort.
The crude birth rate is the number of live births per 1000 inhabitants in a certain year. It is quite easy to calculate and often used to measure the level of fertility. However, a major drawback is that the age structureof the population is not taken into account. For instance, the crude birth rate in an old population would be lower than in a young population.
The crude death rate indicates the number of deaths per 1000 inhabitants in a certain year. It is quite easy to calculate and frequently used to measure the level of mortality. However, a major drawback is that the age structure of the population is not taken into account. For instance, the crude death rate in an old population is higher than in a young population, which does not necessarily imply anything about the real mortality level.
De facto population
The de facto population is a concept under which individuals (or vital events) are recorded (or are attributed) to the geographical area where they were present (or occurred) at a specified time.
Defined benefit pension plans are plans in which the level of pension benefits promised to participating employees is guaranteed; benefits are related by some formula to participants’ length of service and salary and are not totally dependent on either the participants’ contributions or the assets in the fund.
Demographic pressure denotes the ratio between the number of youngsters plus elderly, on the one hand, and the number of 20-64 year olds, on the other hand. It is usually expressed as a percentage. Demographic pressure is a crude measure for the extent to which the "working" have to provide for the "non-working".
A demographic transition is the shift in a population from a traditional demographic regime marked by high fertility and mortality to a modern demographic regime in which fertility and mortality are low.
Demography studies developments in the size, composition, and spatial distribution of populations. The size and the structure of a population changes through births, deaths or spatial motion of its people.
The economically inactive population may be divided into dependents and self-supporting persons. Dependents rely on the efforts of earners for their support; for example, this is the case of housewives and dependent children. A special category of dependents is that of public welfare recipients or persons receiving public assistance.
A disability reflects any limitation or lack of ability that a person experiences in performing an activity in the manner or within the range considered normal for a person, in other words, a limitation in learning, speaking, walking or some other activity (individual dimension).
Divorce is the final legal dissolution of a marriage; a separation of husband and wife that confers on the parties the right to remarriage under civil, religious and/or other provisions in accordance with the laws of the country.
An epidemiological transition or health transition is the period of mortality decline that accompanies the demographic transition. It is characterised by improved health, nutrition and organisation of health services and a change in the causes of death, with mortality from infectious diseases progressively being replaced by mortality from chronic and degenerative diseases and accidents.
Excess male mortality
Excess male mortality is an expression used to describe the excess mortality of men compared to the mortality of women. For a given age or age group it is usually measured as the ratio of the male mortality rate to the female mortality rate.
Fecundability is the probability of conceiving per menstrual cycle. A distinction is made between natural fecundability, in the absence of contraception, and residual fecundability in the opposite instance. The term effective fecundability designates fecundability in terms of conceptions that result in live births only. The conception rate during the period of exposure to risk is used to measure the effectiveness of contraception during periods of contraceptive use.
Fecundity is the biological capacity of a woman, a man or a couple to produce a live birth. Beyond individual variations, fecundity in women reaches its maximum at around age 20, starts decreasing slowly to age 35, and then more rapidly after age 35 until it falls to zero at around age 45 or 50.
Fertility and infertility refer to reproductive performance rather than capacity, and are used according to whether there was actual childbearing or not during the period under review. The fertility level can be assessed per woman, per couple, per group, or for a total population. In addition, fertility, like the number of births, can be distinguished by rank number (parity).
A fertility rate denotes the rate of births to a specified group, usually women, and is generally expressed as births per thousand. The denominator is usually the mid-year population in the stated period. The rates are calculated for groups of women and their women years. Male fertility rates are computed sometimes in an analogous manner. Fertility rates are generally expressed as births per thousand.
Other types of fertility rates are defined as follows:
Line of kinship uniting a child with its father and its mother.
Gender is a notion used in social sciences. It refers to the cultural dimension of sexual differentiation (such as the distribution of power or the breakdown of roles between men and women in society), while the notion of “sex” reflects a universal biological reality.
GNI PPP per capita is gross national income in purchasing power parity (PPP) divided by mid-year population. GNI PPP refers to gross national income converted to “international” dollars using a purchasing power parity conversion factor. International dollars indicate the amount of goods and services one could buy in the United States with a given amount of money.
Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.
A household is a socio-economic unit of one or more persons who share housing and who jointly provide themselves with food and other necessities of life. An individual living alone is considered to be a one-person household. Definitions and classifications of households vary.
Intergenerational equity in economic, psychological, and sociological contexts is the concept or idea of fairness or justice in relationships between children, youth, adults and seniors, particularly in terms of treatment and interactions.
Intergenerational transfers are primarily economic transfers from one generation to the following. In all societies intergenerational transfers are prevalent and influence inequality and growth.
International migration is moving to another country. It can be separated into immigration and emigration. The difference between immigration and emigration is called the immigration balance or simply migration balance. To measure international migration three factors are taken into consideration: space, time and motivation.
International Statistical Classification of Diseases and Related Health Problems (ICD)
This detailed description of known diseases and injuries is published and revised by the World Health Organization. It is used world-wide for morbidity and mortality statistics, reimbursement systems and automated decision support in medicine. Every disease (or group of related diseases) is described with its diagnosis and given a unique code, up to five letters long.
Life expectancy is the average number of years a group of individuals can expect to live at a given age if mortality at each age remains constant in the future. The life expectancy at birth measure is a particular case that represents the mean length of life of individuals based on mortality at all ages. Life expectancy is calculated using life table methods and the reciprocal of life expectancy at birth is the life table death rate.
A life table (also called a mortality table or actuarial table) is a table that shows, for each age, what the probability is that a person of that age will die before his or her next birthday. A number of inferences can be derived, such as the probability of surviving to any particular year of age and the remaining life expectancy for people at different ages.
An expression denoting an individual's passage through life, analysed as a sequence of significant life-events, including birth, marriage, parenthood, divorce, and retirement. In modern socio-demographic literature, the term life-course has replaced that of life-cycle in analysing these sequences of events, because the former carries fewer normative implications than the latter.
Migration is the process of moving to another area, usually implying movement across an administrative boundary. The administrative unit left by the migrant is the place of origin or place of departure; the unit to which the migrant moves is the place of destination or place of arrival. The concept of migration is often not applied to moves made by persons without a fixed place of residence, for example, nomads are excluded from the count of migrants in many countries.
Decisions about migration are shaped by economic, social, and cultural factors, so called push/pull factors. Migration models formalise these determinants. They also may describe the effects of migration at its origin and destination and the interactions between those effects. The simplest of these models are gravity models: the streams between the two areas are directly proportional to the size of their population, and inversely proportional to the distance between them.
Morbidity is the study of illness, sickness, ill-health or disease in a population. Two aspects are considered: the incidence of disease and the prevalence of disease according to whether the new cases of disease are considered or the number of cases existing at one point in time. The compilation of morbidity statistics is hampered by the lack of a sharp distinction between health and the morbid state. Nosology and nosography contribute respectively to the classification and description of diseases.
The demographic concept of mortality deals with the effect of death on the population. Mortality is an important component of population growth. All people die, but the age at which that will happen has strong demographic consequences.
The natural increase of a population is the excess of births over deaths.
The net migration encompasses the number of people moving in minus the number of people moving out of a population. It contributes to overall population growth and can have a negative or a positive sign. Net immigration, or net in-migration, is used when arrivals exceed departures, and net emigration, or net out-migration, when the opposite is true. The sum of arrivals and departures in a country can be used to measure the volume of migration. A similar concept, applied to sub-areas of a country, is the migration turnover.
Net migration rate
The net migration rate is the number of immigrants minus the number of emigrants over a period, divided by the person-years lived by the population of the receiving country over that period. It is expressed as net number of migrants per 1,000 population.
The odds in favour of an event or a proposition are expressed as the ratio of a pair of integers, which is the ratio of the probability that an event will happen to the probability that it will not happen.
A marriage in which a person of one sex has more than one spouse of the opposite sex. Polyandry occurs when a woman has more than one husband, and polygamy when a man has several wives. Polygamy contrasts with monogamy. When a person has two spouses the term bigamy is used.
The actual or de facto population is made up of the people in a specific area on census day, including visitors or transients. This marks a distinction to the resident or de jure population of the area, which only considers those that habitually live in the area. Here, temporary absentees are also included.
The population at risk is the population that is exposed to the occurrence of a vital event, for example, the total population in the case of deaths, the legally married population in the case of divorces and so on.
The extent to which a population increases or decreases over a certain period. It always refers to a certain area and to a certain period (usually one year). Population growth can be measured in numbers of inhabitants, but is usually expressed as a percentage, the so-called growth rate.
All of the measures explicitly or implicitly taken by the authorities aimed at influencing population size, growth, distribution, or composition. A population policy is a set of measures taken by a State to modify the way its population is changing, either by promoting large families or immigration to increase its size, or by encouraging limitation of births to decrease it. A population policy may also aim to modify the distribution of the population over the country by encouraging migration or by displacing populations.
Population projections are calculations that show the future development of a population when certain assumptions are made about the future course of population change, usually with respect to fertility, mortality and migration. They are in general purely formal calculations, developing the implications of the assumptions that are made.
A population register denotes a system of continuous registration in a country. In these registers, every member of the population or every family may be represented, and the register is maintained or updated through information that reaches it through the local registration offices and through registration of any changes of residence. It is usually matched with census results and brought up to date at regular intervals by special checks.
The population structure is the composition of a population according to certain characteristics. In demography, age and sex are the most frequently used characteristics; marital status and region are also important. Other characteristics include nationality, country of birth, religious affiliation, and educational level.
Predicted or expected probabilities can be calculated empirically or from functions that predict or model the probability of an outcome or range of outcomes. This means that if a study is conducted with 100 subjects the outcome can be projected onto the rest of the population.
The propensity of an event is its natural inclination or tendency.
Push and pull factors divide migration models into two broad categories based on migration streams between two areas. Social, economic or demographic variables play decisive roles. These variables are classified as push factors when they characterize repulsion from the area of origin, as pull factors resulting in attraction to the area of destination, and as intervening obstacles between the two areas.
Rate of natural increase
The rate of natural increase is the birth rate minus the death rate, implying the annual rate of population growth without regard for migration. Expressed as a percentage.
Recognition is the act of declaring oneself to be the father or mother of a child born outside marriage. When a child is recognised before or at the time of birth, this recognition is indicated on the birth certificate.
Renewable events are events such as pregnancies, births or migratory moves. They are assigned in an order based on the number of previous events of the same nature for the same person. Together with non-renewable events they comprise the statistics of population change.
A rentier is a person that lives off regular payments of invested capital or off the lease of land.
The study of reproduction or population replacement is concerned with the natural process through which a population replaces its numbers. A distinction is drawn between gross reproduction or gross replacement, where no account is taken of mortality before the end of the reproductive period, and net reproduction or net replacement, in which mortality is taken into account.
Reproduction rates are generally female reproduction rates or maternal reproduction rates. The female net reproduction rate is defined as the average number of live daughters that would be born to a hypothetical female birth cohort, which would be subjected to a set of current age-specific fertility rates and mortality rates.
The retirement age is the age from which the individual is eligible for pension benefits.
The term selection bias or selection effect most often refers to the distortion of a statistical analysis resulting from the method of collecting samples, i.e. when an error in choosing the individuals or groups to take part in a scientific study exists. If the selection bias is not taken into account, any conclusions drawn from the study may be wrong.
Self-supporting persons have sufficient means for their subsistence. They may be earners, rentieror persons of independent means, retired persons or pensioners.
The sex ratio is the ratio of the number of males to the number of females. It is usually expressed as an index value, i.e. the number of males per 100 females.
The standardised death rate denotes the number of people per 1000 inhabitants that would have died in a certain year if the age structure of the population would have had a certain distribution. Standardisation is a method to eliminate the effect of the age structure on the death rate and make death rates of different populations comparable.
The UN Population Division has defined the window of opportunity as period when the proportion of children and youth under 15 years falls below 30% and the proportion of people 65 years and older is still below 15%.