(adapted from The Dictionary of Demography, by Roland Pressat, edited by Christopher Wilson. Oxford: Blackwell Reference, 1985)

Abridged life table. ‘A life table in which values of the life table functions are presented for certain age groups only, rather than for every single year of age.

Acute illness. An illness arising suddenly and lasting only days or weeks.

Age heaping. Concentration of population numbers in certain ages, especially those ending in zero or 5. Age heaping in demographic data may occur when people do not know when they were born or when they are inclined to understate or exaggerate their ages.

Age standardization. A technique for adjusting rates to remove the effects of differences in the age composition of populations.

Aged dependency ratio. The number of people aged 65 years and over per hundred aged 15-64 years.

Ageing index. The number of persons aged 65 and over, or 60 and over, per hundred children under 15. The older the population, the higher the index; indices greater than 100 show that older people outnumber children.

Age-specific death rate. The number of deaths in a year of persons aged x, per thousand persons age x in the mid-year population

Age-specific divorce rate. The number of divorces at age x in a year, per thousand persons aged x in the mid-year population.

Age-specific fertility rate. The number of births in a year to women aged x, per thousand women aged x in the mid-year population.

Age-specific marriage rate. The number of marriages of persons aged x in a year, per thousand persons aged x in the mid-year population.

Area graphs. Graphs in which lines representing data for different categories at a series of dates are ‘stacked’ upon each other, so that the uppermost line represents either 100 per cent or the size of the total. Variations in the width of horizontal bands on the graphs show differences in the numbers or percentages in each category.

Arithmetic change. A population changing arithmetically would increase (or decrease by a constant number of people in each interval .

Average annual increase (or decrease). The average number of people added to (or subtracted from the population each year. Being based on the concept of arithmetic change, it assumes constant annual gains or losses, ignoring the notion that growth is self-reinforcing.

Birthplace method. A procedure for estimating migration from statistics on the state or province of birth of the native-born. Potentially, it can provide information on life-time migration, net migration and gross migration, as well as origins and destinations.

Caretaker ratio. The ratio of females aged 50-64 years to persons 80 years and over.

Cartogram. A map employing proportional symbols to represent areas, such as through drawing squares or circles proportional to the population sizes or other characteristics of the population of each place. Alternatively, the original shape of areas may be scaled up or down in proportion to their population totals 10.8. Cartograms provide a means of emphasising larger populations or the most relevant information.

Cause-specific death rate. A rate measuring the incidence of death from a particular disease.

Census survival ratios. Census-based measures of the proportions surviving from one age group to another. The ratios compare the numbers of males or females in one age group at the first census with their numbers in a later age group at the second census.

Census. A national enumeration of a population at the same time.

Chain migration. Chain migration is the process whereby immigrants encourage and assist relatives and friends to join them. It can have a considerable influence on the origins of immigrants as well as their destinations.

Child dependency ratio. The number of children aged 0-14 years per hundred people aged 15-64 years.

Child-woman ratio. The number of children aged 0-4 per thousand women aged 15-49 in the mid-year population.

Choropleth map. A map employing shading of areas to portray distribution.

Chronic illness. An illness of long duration, lasting months or years.

Closed population. One with no migration arrivals or departures.

Cohort analysis. An approach to demographic analysis employing data for cohorts to study the experiences of the same groups of people at different points in time.

Cohort component method of projection. A projection method that entails calculating the future size of individual birth cohorts through taking into account the effects of fertility, mortality and migration – that is, the components of change.

Cohort life table. Life tables describing the mortality through time of real cohorts rather than mortality in one period. They are also known as generational life tables.

Complete life table. Life tables for single years of age. They are also known as unabridged life tables.

Completed fertility. The total children ever born to women at the end of their reproductive years.

Components of growth. The sources of population gains and losses, namely natural increase and net migration.

Conference posters. Posters used at scientific and professional gatherings to provide summaries of.

Cross-sectional analysis. An approach to demographic analysis employing data for years or points in time, such as from censuses, vital statistics and surveys. Also known as period analysis.

Crude birth rate. The number of live births in a year per thousand people in the mid-year population.

Crude death rate. The number of deaths in a year per thousand people in the mid-year population.

Crude divorce rate. The number of divorces in a year per thousand people in the mid-year population.

Crude marriage rate. The number of marriages in a year per thousand people in the mid-year population.

CSR method. A procedure for estimating net migration using census survival ratios.

Cumulative frequencies. The number of cases or observations in each category or group are called frequencies. For any category, the cumulative frequency is the total number of cases in that and previous categories.

De facto census. A census that counts people at their locations on the night of the census.

De jure census. A census that counts people where they usually live.

Deductive research. Research that proceeds from a theory to its testing with observations.

Demographic balancing equation. An expression stating that population growth is equal to the sum of its components, namely natural increase and net migration.

Demographic transition. Refers to the movement of death and birth rates in a society, from a situation where both are high – in the pre-transition stage – to one where both are low – in the post-transition stage. The interval separating the two is the transition itself, during which substantial and rapid population growth often occurs.

Demographic translation. Techniques for establishing the relations between cohort and period measures of demographic processes.

Demography. The scientific study of human populations.

Dependency ratios. The number children and aged persons per hundred people of working age.

Direct standardization. A technique for calculating comparative rates by assuming that each population has the same ‘standard’ composition in terms of age structure or another characteristic.

Disordered cohort flow. The movement of distinctive cohorts through the age structure, occasioning sudden changes rather than the maintenance of a continuous trend.

Dot map. A map employing dots of uniform or varying sizes to portray distribution patterns. Each dot may represent individuals or aggregates such as 100 or 1,000 people 10.3.

Doubling time. The number of years that a population would take to double; the doubling time provides a readily understood measure of the pace of change that a particular growth rate implies.

Duration-specific divorce rate. The number of divorces after n years of marriage per thousand people married n years.

Dwelling occupancy rate. A measure of the average number of persons per dwelling, obtained by dividing the total number of persons in private dwellings by the total number of occupied private dwellings. Also known as the housing occupancy rate .

Economic dependency ratio. The number of people not in the labour force per hundred in the labour force.

Endogenous causes of death. Causes due to internal agents operating within the body, such as sensesence. Exogenous causes, however, are now known to cause degenerative and other diseases once attributed to endogenous factors alone.

Epidemiologic transition. A theory describing and explaining variations in countries’ experience of mortality changes through time.

Exact age. A person’s actual age in years, months and days. Demographic use of the term is most common in life tables, where certain functions refer to ages on birthdays. In contrast, everyday usage measures people’s ages mainly in completed years, as age last birthday.

Exogenous causes of death. Causes arising from agents outside the body, including infections, accidents, environmental pollution and lifestyle factors, such as diet and smoking.

Exponential change. A constant rate of increase or decrease in which change is compounding at every moment. While exponential change recognizes that growth is self-reinforcing, populations seldom experience constant rates of growth or decline for very long

External migration. A synonym for international migration.

Familism. A family-oriented lifestyle.

Family. A grouping based on kinship. Demographers conducting research on the family study co-resident kin and wider networks of kin who are in contact with each other.

Fertility differentials. Differences in the fertility of people according to socio-economic and other characteristics.

Fertility. ‘The childbearing performance of individuals, couples, groups or populations’.

Fetal death. A death of a fetus; includes stillbirths, miscarriages (spontaneous abortions, and abortions.

Fictitious cohort. See synthetic cohort.

Flow map. A map employing arrows or flow lines of different widths to depict linkages between places – in terms of the movement of people, or of goods and services, between them. The most common demographic application is in the mapping of migration.

Forward survival. An approach to estimating age-specific net migration in which survival ratios (from life tables or censuses are applied to the initial population to estimate the number of survivors at the end of the period, that is working forward through time. The net migration is the difference between the estimated number of survivors at each age and the total enumerated in each age group at the end of the interval.

General divorce rate. Divorces in a year per 1000 people aged 15 years and over in the mid-year population.

General fertility rate. Live births in a year per 1000 women aged 15-49 years in the mid-year population.

General marriage rate. Marriages in a year per 1000 people aged 15 years and over in the mid-year population.

Generation. A term with different meanings in different contexts, including the time interval between birth and parenthood, a birth cohort and an age-group of descendents within a family.

Geocoding. An approach to recording the locations of areas or addresses by expressing locations as co-ordinates on a standard reference grid. Geocoding aims to facilitate accurate tabulation and mapping.

Geographic information systems (GIS. A GIS consists of a database of spatially referenced information, together with the procedures for storing, retrieving, analysing and displaying it.

Geometric change. A constant rate of increase or decrease in which change is compounding at constant intervals, such as at the end of every year.

Gini index. ‘A quantitative estimate of the extent to which certain characteristics (e.g. income are unequally distributed between subgroups of the population’.

Gross growth. The sum of all additions to a population during a period of time, arising from births and inward migration.

Gross reproduction rate. The sum of the (single year age-specific fertility rates for female births in a given year. It represents the average number of daughters a woman would have if she experienced, over her reproductive years, the age-specific fertility rates of the given year.

Growth rate. The annual rate of change in the size of a population.

Household headship method of projection. A method for calculating household projections using an existing population projection by age and sex, together with statistics on the proportion of household heads belonging to each age-sex group.

Householder. An individual who owns or rents a dwelling.

Housing density. A measure of the relationship between land area and the number of dwellings.

Housing occupancy rate. A synonym for dwelling occupancy rate.

Housing unit method of projection. This method uses information on existing dwellings and projected dwelling commencements and demolitions. The projected population is obtained by multiplying the projected number of occupied dwellings by the average number of persons per occupied dwelling.

Human development index. A measure of the relative socio-economic progress of countries, published by the United Nations. The index is a composite of three components of human development, namely longevity, knowledge, and standard of living.

Hypothesis. A testable statement describing the relationship between two or more variables.

Immediate cause of death. The final disease or condition resulting in death, as distinct from the underlying cause of death.

Incidence of a disease. The number of new cases of a disease counted in the period of observation.

Incidence rate. A rate measuring the likelihood of developing a disease or health condition. It is calculated by dividing the number of new cases by the mid-period population, and multiplying by 1,000 or 100,000.

Index of concentration. A measure of the degree of correspondence between population and land area. It is based on the index of dissimilarity and compares the percentage of the population in each region or place with the percentage of the total land in each region.

Index of dissimilarity. A measure of the extent of non-overlap, or dissimilarity, between two percentage distributions. It provides a single figure summarizing the overall difference between two or more populations in relation to their age structures, occupational distributions, ethnic composition or other characteristics. It also has applications in comparing the same population at different dates .

Index of diversity. A measure of the heterogeneity of populations. It is employed in the analysis of nominal data, such as statistics on languages and religions, for which there is no gradation between categories. In its standardized form, the index of diversity ranges from 0 (homogeneity – all members of the population are in one category to 1 (heterogeneity– the population is evenly distributed through all categories.

Index of excess male mortality. Another name for the sex-ratio of age-specific death rates.

Index of segregation. A form of the index of dissimilarity measuring the extent to which an ethnic group differs in its spatial distribution from the rest of the population, or from another group in the population. Typical applications are comparisons of white and non-white populations, or immigrants and the native-born. The greater the dissimilarity between the spatial distributions of the two groups, the greater the ethnic segregation.

Index or redistribution. A measure, based on the index of dissimilarity, summarizing the extent of changes in population distribution. It is calculated from percentages denoting the spatial distribution of the same population at two dates.

Indicator methods. Estimating and projecting population numbers with reference to ‘indicator variables’, such as the number of housing units and electoral roll registrations, changes in which are associated with changes in the total population.

Indirect standardization. A technique for calculating comparative rates by assuming that each population is subject to the same ‘standard’ set of age-specific, or other characteristic-specific, rates.

Inductive research. Research that proceeds from observations to the construction of a theory.

Information literacy. Knowing how to find, evaluate and use needed information. Information literacy comprises skills in library research as well as in information technology.

Intercensal estimates. Estimates of population numbers between two existing censuses. They are more accurate than postcensal estimates, because there are two reference points together with observed data on births, deaths and migration for all of the intervening years.

Internal migration. Migration between communities within the same country.

International migration. Migration between countries.

Intrinsic birth rate. The birth rate of a stable population.

Intrinsic death rate. The death rate of a stable population.

Intrinsic rate of natural increase. The rate of natural increase of a stable population. The rate is ‘intrinsic’ to, or inherent within, the population concerned because it is based solely on its age-specific fertility and mortality in the year of observation.

Key terms and formulae related to population growth

Labour force projections. Calculations of the future size of the labour force. The simplest approach to labour force projections, as well as that most consistent with other projections, is to take figures for the total population produced by the cohort component method and calculate from them the projected population in the labour force. This is accomplished by multiplying the projected numbers in each age-sex group by an assumed labour force participation rate for each group.

Lexis diagram. A square grid depicting the location of demographic events in time.

Life expectancy. ‘The average number of additional years a person would live if the mortality conditions implied by a particular life table applied.’

Life table functions. The measures of mortality and survival in a life table.

Life table survival ratios. Life table measures of the proportions surviving from one age group to another, calculated from the Lx function .

Life table. A detailed description of mortality in a population through a set of age-specific measures of deaths, survival and life expectancy.

Living arrangement method of projection. An approach to household and family projections using statistics on the proportions of the population in different types of living arrangements. The projections are obtained by partitioning projections of the total population by age and sex into the required categories of living arrangements.

Local migration. Migration within a community, such as a city, town or village. Also known as residential mobility.

Location quotient. A statistic obtained through dividing a percentage for one population by a corresponding percentage for another (base or standard population. It measures whether a characteristic is under-represented or over-represented in the first population compared with the second.

Logistic curve. A mathematical model of population growth which envisages that population growth follows an S-shaped curve – from slow initial growth to more rapid growth and, finally, to a plateau in population numbers. Although the logistic curve recognizes that numbers cannot increase indefinitely, it has had little success in forecasting national population growth

Longitudinal analysis. A synonym for cohort analysis.

Lorenz curve. A curve showing the extent to which a given distribution is uneven compared with an even distribution. The curve is plotted on a scatter diagram, with axes of equal length, from data on the cumulative frequency distributions of two variables. The greater the curvature of the line, the greater the deviation from an even distribution.

LTSR method. A procedure for estimating net migration using life table survival ratios.

Male excess mortality. The excess of male deaths over female deaths, measured by the sex ratio of age-specific death rates.

Market segmentation. A concept describing a situation where there is not a single mass market for goods and services, but multiple markets – each consisting of groups of consumers with different needs and purchasing behaviours.

Marriage. Either ‘a legal union of persons of the opposite sex’ or, more broadly, a commitment to a union, whether or not formally recognized through a legal or religious ceremony.

Maternal mortality rate. The number of maternal deaths per 10,000 or 100,000 live births. Maternal deaths are those due to causes connected with pregnancy, labour or the puerperium (lying-in period – the period of approximately six weeks after childbirth, during which the uterus returns to normal.

Mean age at childbearing. ‘The mean age of mothers at the birth of their children.’

Mean age. The average age of a group or population.

Mean length of a generation. ‘The average age of mothers at the birth of their daughters. This is regarded as the mean interval separating the births of one generation from those of the next.’

Median age at divorce. The age above and below which half the divorces occur.

Median age at marriage. The age above and below which half the marriages occur.

Median age. The middle age in a group or population; the age which half are above and half are below.

Mid-year population. The observed population total at mid-year, or the average of the population at the start and end of the year; often employed as the denominator for demographic rates.

Migration effectiveness. The ratio of net migration to gross migration, the lower the ratio the less the effectiveness of migration as a process of population redistribution.

Migration expectancy. An estimate, derived using life table methods, of the average number of migrations individuals at each age may be expected to make during the rest of their lives.

Migration interval. The interval during which migration is observed, such as between two censuses.

Migration. Population movement entailing a change in the usual place of residence.

Mobility. All forms of population movement, whether temporary or permanent.

Modal age. The most frequently occurring age in a group or population.

Model life tables. Sets of hypothetical life tables spanning a wide range of life expectancies as well as different patterns of age-specific mortality .

Model stable populations. Sets of stable populations corresponding to a wide range of mortality patterns, mortality levels and intrinsic rates of natural increase. They have been produced in conjunction with model life tables .

Morbidity. ‘The state of illness and disability in a population.’

Mortality differentials. Mortality differences between population groups defined in terms of age, sex, marital status, socio-economic characteristics or place of residence.

Mortality. ‘The process whereby deaths occur in a population.’

Movers. A synonym for migrants.

Multiregional projection model. A technique that uses the methods of matrix algebra to produce cohort component projections simultaneously for a number of sub-populations.

Natural fertility. ‘The fertility of populations not practising contraception or induced abortion.’

Natural increase. The excess of births over deaths.

Negative momentum. This occurs when the projected stationary population is smaller than the present population. It denotes potential for decline inherent within the age structure, arising when smaller cohorts are destined to replace large cohorts at older ages in the future..

Neonatal mortality rate. A measure of the risk of mortality among the newborn, expressed as the number of deaths in the first 28 days of life per 1,000 live births.

Net growth (or decline. The difference between the size of a population at the start and the end of an interval; in a growing population it is the excess of gains over losses.

Net migration. The difference between the numbers of inward and outward migrations.

Net reproduction rate. A measure of the number of daughters who will live to replace their mothers in the future. It is the sum of the (single year age-specific fertility rates for female births in a given year, multiplied by the probability of daughters surviving to the age of mothers at their birth.

Nodal regions. Nodal regions consist of central places and their hinterlands. They are delimited with reference to spatial interactions, through identifying places that are linked together economically, socially or politically, such as through trade, commuting, shopping or use of medical and educational services.

Open population. A population experiencing inward and outward migration.

Open-ended age interval. An age interval, such as ‘85 years and over’ for which no upper age limit is specified.

Outlining. Preparing an outline of a paper or report to establish its overall structure, either through writing a synopsis or through creating a set of headings and subheadings.

Paradox of the life table. An increase in life expectancy with age, which occurs because life expectancy at birth is often lower than life expectancy at age one, and sometimes even at age five. The paradox reflects high rates of infant and child mortality; those who survive the high-risk period have better prospects.

Partial displacement migration. Migrations that result in only a partial change in the locations visited regularly for work, shopping, schooling and recreation. Housing is often the main consideration in such movement. See also total displacement migration.

Percentage change. The absolute change in the size of a population per hundred people in the initial population. Percentage change provides a means of comparing developments in different populations, or different periods of time, by gauging the amount of change relative to initial numbers. It is always based on numbers at the start of the period.

Percentage. A proportion multiplied by 100.

Perinatal mortality rate. A measure of mortality between 28 weeks gestation and one week after delivery. Use of this combined figure for stillbirths and early neonatal mortality mainly reflects that the causes of death are similar.

Period analysis. A synonym for cross-sectional analysis.

Period life table. A life table based on the age-specific mortality observed in a particular period of time, such as a single year or a three year interval.

Person years. The sum of all the years members of a population have lived, during a fixed interval or over their whole lives.

Pie graphs. A graph in which a circle represents a total and sectors within it represent components of the total.

Population ageing. A process entailing an increase in the percentage of the population in older ages. Also known as demographic ageing.

Population ageing. Population ageing, or demographic ageing, entails an increase in the percentage of the population in older ages, often taken as 65 years and over.

Population at risk. The population that could potentially experience a particular demographic event, such as giving birth or migrating, in a specific period of time.

Population density. ‘A comparative measure of the number of people resident within a standard unit of area’, such as persons per square kilometer or per square mile.

Population estimates. Calculations of the size of a population, usually for the present year or the recent past. Statistical agencies prepare estimates of the current population, to provide up-to-date information for years in which there is no census. Estimates are based on observed data about population changes (births, deaths and migration, whereas projections refer to dates for which there are no observed data, especially future years.

Population forecast. A projection representing what is considered to be the most likely future course of change in the population.

Population momentum. The potential for growth (or decline that is inherent within an age structure, assuming that the population experiences replacement level fertility (as well as constant mortality and zero migration in the future, and ultimately becomes stationary. Whereas the intrinsic rate of natural increase indicates the growth rate implicit in current fertility and mortality, ignoring the age structure, population momentum shows the growth potential implied by the age structure alone (Pressat 1985: 150. Population momentum is measured as the difference in size between the present population and the future stationary population..

Population projections. Calculations of population numbers at dates for which there are no observed data, especially future years. Reverse, or backwards, projection for past years is also possible.

Population pyramid. A bar graph depicting the numbers or percentages of males and females in each age group.

Population replacement. The share of gross growth absorbed in replacing deaths and migration departures. Population replacement is equal to gross growth minus net growth.

Population surveys. These collect data from a sample of the population on an aspect of demography such as fertility, mortality, migration, employment, families, health and housing. Compared with a full census, they can provide more detailed data on certain subjects and are less costly to conduct.

Population turnover. The sum of all population losses and gains during a period of time. Population turnover captures the total magnitude of changes in membership that a population experiences – the total of births, deaths, migration arrivals and migration departures, all of which are treated as positive numbers.

Positive momentum. This occurs when the projected stationary population is larger than the present population. It denotes growth potential inherent within the age structure, arising when large cohorts are destined to replace smaller cohorts at older ages in the future.

Postcensal estimates. Estimates of population numbers since the last census. See also population estimates and intercensal estimates.

Post-neonatal mortality rate. A measure of the risk of mortality beyond the neonatal period, expressed as the number of deaths from 29 days to one year of age per 1,000 live births.

Prevalence of a disease. The total number of cases of a disease counted in a period of observation.

Prevalence rate. A rate measuring the likelihood of having a disease or health condition in a specified period. It is obtained by dividing the total cases by the mid-period population, and multiplying by 1,000 or 100,000.

Primary data. Data collected for specific purposes, by or for those who wish to use the information.

Probability of dying. The relative frequency of death, such as between adjacent ages. In life tables it is measured by the qx function.

Probability of surviving. The relative frequency of surviving, such as from one age to the next. In life tables it is measured by the px function.

Probability. The ratio of the number of demographic events to the initial population at risk of experiencing them.

Proportion. A ratio in which the denominator includes the numerator.

Proximate determinants of fertility. The immediate causes of fertility change through which the underlying social and economic causes operate. Bongaarts and Potter (1983 attributed variations in the total fertility rate mainly to the influence of four proximate determinants influencing the duration of the reproductive period and the rate of childbearing within it namely: marriage (or first cohabitation, contraception, induced abortion and post-partum infecundability.

Rate of natural increase. The annual rate of change in the size of the population resulting from the excess (or deficit of births over deaths.

Rate of net migration. The annual rate of change in the size of the population resulting from the excess (or deficit of inward migration over outward migration.

Rate ratio. The ratio of two rates, used to measure their relative magnitude.

Rate. A measure comparing the number of demographic events (e.g. births with the size of the population at risk of experiencing the event.

Ratio method of projection. A technique for projecting small area populations. It assumes either that the proportion of the total population living in each subarea remains constant through time, or that it varies according to a predefined pattern. Small area projections are obtained by subdividing the projected total population according to the specified proportions.

Ratio. The size of a number relative to another convenient number.

Real cohort. A cohort for which there is actual observed information through time.

Rectangularization of the survival curve. The tendency over time for the proportions surviving at younger and middle ages to approach 100 per cent, with the proportions declining only in the oldest ages.

Relational model life tables. A technique for calculating further life tables from a ‘standard’ life table. This is accomplished by varying two or more parameters that describe the relationship between the ‘standard’ lx values and the ‘predicted’ lx values.

Relative risk. A measure of the extent to which a particular characteristic is associated with an increase in the prevalence of a disease, or in mortality from it. It is calculated from ratios of incidence rates or mortality rates.

Replacement-level fertility. The level of childbearing at which women of reproductive age have sufficient daughters to replace, exactly, their own numbers in the population. It takes into account the survival of daughters to the age at which their mothers bore them, and occurs, therefore, when the levels of fertility and mortality produce a net reproduction rate of one.

Research design. ‘A system of test environments or conditions’.

Residential mobility. See local migration.

Reverse survival. An approach to estimating age-specific net migration in which reverse survival ratios are applied to the end-of-period population to estimate the size of the initial population, that is working backwards through time. The net migration is the difference between the estimated initial numbers at each age and the total enumerated in each age group at the start of the interval. Compared with forward survival, this method tends to yield higher estimates because they include migrants who died during the interval.

Room occupancy rate. A measure of the crowding of dwellings, calculated as the average number of persons per room.

Second demographic transition. A theory which seeks to describe and explain family building behaviour in post-transition Europe and, by extension, circumstances in a number of other low fertility societies. A particular concern is the shift to below-replacement fertility.

Secondary data. Information originally intended for other purposes, or collected by another researcher or organization. It includes data intended for general administrative and research use, including population censuses, vital statistics and surveys undertaken by government statistical agencies.

Settlement hierarchy. A set of urban centres in a country or region, sorted into categories according to the size of their populations. Also known as an urban hierarchy.

Sex ratio of age-specific death rates. Ratios of the male age-specific death rates to the corresponding female age-specific death rates. Since male mortality is commonly higher, the figure is also known as the index of excess male mortality.

Sex ratio. The ratio of the number of males to the number of females, usually expressed as males per hundred females.

Stable population. ‘A population which is closed to migration and has an unchanging age-sex structure that increases (or decreases in size at a constant rate.’

Standardized mortality ratio. The ratio of observed to expected deaths, the latter being obtained through assuming that the population is subject to a standard set of age-specific death rates (see indirect standardization).

Stationary population. ‘A population closed to migration with unchanging age structure and mortality in which the annual number of births is equal to the number of deaths, producing a zero growth rate.’

Statistical reporting. Producing an article or report that summarises and interprets a given set of statistics. The data, such as in a newly-published statistical bulletin, define the scope and content of the report.

Stayers. People who did not move during a migration interval.

Stillbirth rate. The rate of fetal deaths, after 28 weeks gestation, per 1000 live births and stillbirths.

Survival ratios. Measures of the proportions surviving from one age to the next. See also census survival ratios and life table survival ratios.

Symmetrical and asymmetrical age distributions. Symmetrical age distributions have similar numbers of males and females in corresponding age groups. Asymmetrical age distributions have dissimilar numbers of males and females in corresponding age groups.

Synthetic [hypothetical] cohort. ‘A theoretical concept by which measures can be calculated for a particular period analogous to those calculable for a true [or real] cohort.’

Theory. ‘A set of logical and empirical statements that provides an explanation of some phenomenon.’

Time: point, interval, duration. Measures of time referring, respectively, to (i specific dates), (ii the period between two dates), and (iii the time since the date of an event, such as birth or marriage).

Total displacement migration. Migrations in which the movers sever links with all the locations they once regularly visited on a daily or weekly basis, such as places of work, shopping, schooling and recreation. See also partial displacement migration.

Total fertility rate. The sum of the (single year age-specific fertility rates in a given year. It represents the average number of children a woman would have if she experienced, over her reproductive span, the age-specific fertility rates of the given year.

Total marital fertility rate. The sum of the (single year age-specific fertility rates of married women in a given year. It represents the average number of children a married woman would have if she experienced, over her reproductive span, the age-specific marital fertility rates of the given year.

Underlying cause of death. The disease or injury that initiated the train of events leading directly to death.

Uniform regions. Areas that are relatively homogenous in terms of the phenomenon in question.

Unimodal and bimodal age distributions. Unimodal age distributions have a pronounced peak in one age group, such as may occur in populations with many recent immigrants. Bimodal age distributions have two peaks, for instance when a population has a predominance of parents and their children.

Vital statistics. Statistics on events that change the composition of the population, especially births and deaths. Other events – marriages, divorces, adoptions and migration – are sometimes included as well. The statistics are products of official registration systems.

VS method. A method of estimating net migration from vital statistics on births and deaths, together with census data. Since population change is equal to natural increase plus net migration, net migration is equal to population change minus natural increase.

Young, mature and old populations. Terms used to describe age pyramids according to their representation of children, middle-aged and older persons.

Zero population growth (ZPG. Denotes a situation where a population has a growth rate of zero. ZPG is achieved if additions to the population from births and inward migration exactly balance losses from deaths and outward migration.

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