Glossary of main concepts, terms and symbols
used in the demographic studies.
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(*) Amongst various sources, this glossary of terms has been prepared by the consultation of the
following texts:
- Chiang, C.L. (1968), "Introduction to Stochastic Processes in Biostatistic", John Wiley, New York.
- Cox, P.R., (1970), "Demography", Cambridge University Press, Bentley House, London.
- Hageman, L.A. and Young, D.M., (1981), " Applied Iterative Methods", Academic Press, Inc.- San
Diego, California.
- IUSSP, (1982), "Multilingual Demographic Dictionary", Ordina Edition, Liège, Belgium.
- Keyfitz, N., (1968), " Introduction to the Mathematics of Population", Addison - Wesley, Reading,
Massachusetts.
- Pitchford, J.D., (1974), "Population in Economic Growth", North Holland Publishing, Amsterdam
London
- Shryock, H.S. and Siegel J.S. (1976), " The Methods and Materials of Demography", Academic Press,
New York
- The World Bank, (1998), "World Development Indicators", Washington, USA.
- United Nations, (1996), "Demographic Yearbook", New Yotk.
- United Nations Population Fund, (1993), "Readings in Population Research Methodology", Social
Development Center Chicago, Illinois, USA.
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Demographical and statistical terms Symbols
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* A *
- abortion
is defined, with reference to the woman, as any interruption of pregnancy
before 28 weeeks of gestation with a dead foetus. There are two major
categories of abortion: spontaneous and induced. Induced abortions are
those initiated by deliberate action undertaken with the intention of
terminating pregnancy; all other abortions are considered as spontaneous.
- abortion rate
is a measure of the frequency of abortion in a population during a given
period, usually a year. Abortions may be related to the total population
or to the number of women in the reproductive ages, and may be specific
for age, parity or any other characteristic.
- abridged life table
is one in which most functions are given only for certain pivotal ages,
frequently spaced at five or ten-year intervals after infancy.
It is a life table computed by age intervals of 5 or 10 years, instead of
single years of age. The youngest intervals are usually specified as age
0-1, 1-4. The oldest age interval is an open interval.
- absolute average difference ISC
estimates the degree of fitting between observed and theoretical data.
- abstinence
abstinence from coitus, particularly periodic abstinence is often included
among contraceptive or birth control method.
- adjusted rates
rates which have been standardized for age and/or other compositional
characteristics in order to make them comparable with each other.
- age and duration-specific divorce rates
are given by the number of divorces of women (or men) aged x to x+n
and married t to t+k years, divided by the persons years lived by the
corresponding married population.
- age-child ratio IV or ACR
defined as the ratio of the elderly (age 65 and older) to the population in
in younger ages (under age 15).
- age dependency ratio ID
is the ratio of the young and the elderly to the adult population.
- age distribution of a population
when the distribution of a population is given by individual years of age.
- age groups
represents the age distribution of a population, which may be five-year
age groups, also called quinquennial age groups or broad age groups,
such as 0-19 years, 20-59 years, 60 years and over.
- age of maximum value of fertility rates. FXM
age corresponding to the maximum value of a given age-specific
fertility rates distribution.
- age heaping
tendency of some people to round their ages to numbers ending in zero
or five or to report certain ages instead of others. Also known as "age
preference" or "digit preference".
- age of maximum value of the resistance function XM
age corresponding to the maximum value of resistance function.
- age-pattern of fertility
relative (proportionate) distribution of a set of age-specific fertility rates.
It espressed the relative contribution of each age group to total fertility.
- age-sex structure of a population
the number or proportion of the total population which falls in each
category of a cross-classification by sex and age (either single years or
age groupings).
- age-specific death (mortality rate), see Central death rate.
- age-specific divorce rate
is given by the number of divorces of women (or men) aged x to x+n
divided by the number of the person years lived by married women
(or men) between ages x and x+n.
The denominator may be also represented by the total number of the
person years lived at age x to x+n by women or men.
- age-specific fertility rate f(x) or F(x)
rate calculated by relating births generated during a give period from
a number of women of age x (or of age x,x+h) to the quantity of
women living of age x (or in age x, x+h).
- age-specific first marriage rate
is given by the number of first marriages of women (or men) aged x
to x+n in a given year divided by the person years of women (or men)
aged x to x+n who are exposed to the "risk" of first marriage.
As second kind, the denominator may be represented by the total
number of person years lived by men or women aged x to x+n.
- age-specific first net migration rate
is computed as the amount of net migration (difference between
immigration and emigration) at a given age per 1000 of the midyear
population at this age.
- age-specific probability of emigration
the annual age-specific probability of emigration between exat age x
and x+1 is computed as the number of emigrants at a given age during
the year related to midyear population at age x, plus half of the deaths
during the year at age x.
- age-specific remarriage rate
is given by the total number of remarriages for persons aged x to x+n,
divided by the total number of person years lived by divorced, plus
the number of the widowed between age x to x+n.
- age standardization
a procedure of adjustment of crude rates ( birth, death or other rates)
designed to reduce the effect of differences in age structure when
comparing rates.
- average annual rate of change
the average per cent increase or decrease per annum required to
account for observed numerical change in size between two dates.
- average family size
is the number of children for couple.
- average parity
is the mean number of children even born per woman.
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Demographical and statistical terms Symbols
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* B *
- balancing equation
addition of the net balance of the components of change (births, deaths
and migration) between two dates to the total population at the earlier
date in order to estimate the population count as of the later date. This
may be compared with a population count for the later date.
- basal body temperature method
refers to the contraceptive metod in which the woman keeps track of her
temperature to identify the safe fecond period..
- birth at term
birth which is non premature.
- birth cohort
a sub-population born in a particular year or set of years, the members
of which therefore are of the same age range and pass through life
together Their progress may be charted by following them at successively
older ages in consecutive censuses or enumerations.
- birth intervals
time elapsed (months) between successive live births, or the intervals
between marriage and the first birth, between the first and the second bitrh;
and so on.
- birth order
the ordinal number of a given live birth in relation to all previous live birth
in relation to all previuos live births of the same woman.
- birth probabilities
the annual probability that a woman will have a live birth within a specified
year of age.
- birth rate b(t)
rate calculated by relating the number of live births observed in a
population during a given period to the size of the population during
the period. This rate is usually stated per 1,000, and the most usual
period is one year.
- birth spacing
is commonly used to refer to the deliberate efforts of couples to pospone
a birth.
- birth timing
is the interval between marriage and the first birth, and intervals between
successive births.
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Demographical and statistical terms Symbols
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* C *
- cause of death
the disease or event that caused death.
- cause-specific death rates
the annual number of deaths from a given cause per 100000 mid-year
population . Cause-specific rates are reported for sex-age groups, local
areas, and sometimes other categories.
- census
a complete count or enumeration of a population conducted under the
auspices of some governmental authority. This term denotes that an attempt
was made to enumerate every member of the population concerned and to
achieve complete coverage of the population. A micro census is limited to a
sample of the population, usually large in size, and belongs in the category
of sample surveys. Censuses or surveys are sometimes preceded by pre-tests
or pilot surveys.
- central death rate at age x _{n }m _{x }; m(x) ; M(x)
is the ratio of deaths between ages x and x+n to the mean population alive at
that age
- childbearing ages
the span wìthin which women are capable of bearing children, generally
taken to be from age 15 to age 49.
- childbirth
is the actual process of expulsion of the foetus. (see delivery)
- childlessness
refer to the state of a women, man or couple who have been so far infertile.
- child-women ratio
number of children aged 0-4 (or 5-9) per 1000 women of childbearing age
( f.e., 15-49) at the time they born those children.
- closed population
in which there is no migration either inwards or outwards and whose growth
is determined solely by fertility and mortality, and therefore depends entirely
on the difference between births and deaths.
- coding scheme
the coding scheme establishes a correspondence between an entry and its
translation into numeric or alphabetic codes.
- coefficient of determination R^{2 }or RR
estimates the fitting degree among observed data and theoretical data.
- cohort
denotes a group of persons who experience a certain event in a specific period
of time.
- cohort fertility
the fertility experienced over their life-time of a group of women or men who
form a birth or marriage cohort.
- cohort fertility rate
fertility of real cohorts of women, obtained by tracing them longitudinally
from year to year. Cohort rates may be age-specific or cumulative.
For completed cohorts which have passed their 49^{th }birthday, it is possible
to compute for each a general fertility rate, total fertility rate, and other summary
measures.
- cohort life table
records the actual mortality experience of a particular group of individuals
(the cohort) from birth to the death of the last member of the group.
- completed fertility
is the cumulative fertility until the date when all members of the cohort have
reached the end of the reproductive period.
- complete life-table
a life table computed for every single year of age from birth to the oldest
specified age.
- contraception
this term refers to measure which are taken in order to prevent sexual
intercourse or coitus from resulting in conception, or to the conscious effort
of couples to avoid conception through rhythm, withdrawal, abstinence, male
and female sterilization, or use of contraceptives: intrauterine devise (IUD),
oral contraceptives, injectable contraceptives, condom, spermicide, and
diaphragm.
- crude birth rate at time t b(t) or Br
when all live births are related to the entire population or subpopulation.
- crude death rate at time t d(t) or Dr
this is an annual rate and consists of the ratio of the annual number of deaths
occurring during a calendar year per 1000 mid-year population.
- crude divorce rate
is given by the total number of the divorces in a year divided by the total
number of person years lived by the population, or per 1000 mid-year
population. Similar rates may be considered setting in the denominator
the number of persons above age 15, or the total number of exinting
marriages (identical to the number of married men or women ) exposed to
risk of divorce.
- crude emigration rate
represents the amount of emigration per 1000 of the mid-year population of
a country .
- crude first marriage rate
is given by the total number of marriages of women or men in a year, divided
by the number of person years lived by the single population of women or
men. We have a similar rate when in the denominator is the single population
of age groups that may legally marry (for convenience 15 is taken as minimum
age).
- crude gross migration rate
represents the amount of emigration plus immigration per 1000 of the mid-year
population of a country .
- crude immigration rate
represents the amount of immigration per 1000 of the mid-year population of
a country .
- crude marriage rate
is the total number of marriages divided by the total number of person years
lived by the total mid-year population, or by the population aged 15 or more.
- crude net migration rate
represents the difference between immigration and emigration per 1000 of the
mid-year population of a country .
- crude rate of natural increase r(t)
is the difference between the crude birth rate and the crude death rate.
- crude remarriage rate
represents the total number of remarriages in a year, divided by the sum of
widowed and divorced men or women exposed to the possibility of remarriage.
- cumulative fertility
it is obtained when the age-specific fertility rates are summed from the cohort’s
beginning of exposure to risk until some later date.
- cumulative net fertility
represents the sum of the products of the fertility rates of the cohort by the
probability of survival of the women to successive aged .
- current life table
considers the mortality experience of a given population during one short
period of time.
- curve fitting
curve fitting consists of finding a suitable equation to represent the trend
of the examined data
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Demographical and statistical terms Symbols
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* D *
- death
is the permanent disappearance of all evidence of life at any time after live
birth has taken place ( post natal cessation of vital functions capability of
resuscitation ). This definition therefore excludes foetal deaths.
- deaths at age x D(x)
represents the number of deaths from age zero and exact age x observed in
the life table
- deaths at age exact x d(x)
are given by the first derivative of the life function
- deaths between ages x and age x+n d _{x,x+n }
deaths calculated by the difference between survivors of the life table of
age x and of age x+n
- death rates by causes
are the annual number of deaths in each cause group reported for the year
per the corresponding mid-year population.
- delivery
is called the actual process of expulsion of the foetus.
- demographic model
consists of a theoretical construct representing the evolution of a population
(of individuals, couples, families, households, etc.) and its structure on the
basis of its initial state and the effect of various demographic variables (such
as fertility, fecondability, mortality, etc.). In a static model these variables
remain constant; in a dynamic model these variables are allowed to change
over time.
- demographic transition
the historical shift of birth and death rates from high to low levels in
population. The decline of mortality usually precedes the decline in
fertility, thus resulting in rapid population growth during the transition
period.
- density of population
is the number of person in a year total population per square kilometre
of total surface area of a country.
- dependency ratio ID
persons aged 0-14 and over 65 of given sex per person 15-64 of given sex.
- developed (or more developed) countries
countries that have higher levels of per capita income, industrialization
and modernization.
- developing (or less developed) countries
countries that have lower levels of per capita income, industrialization,
and modernization
- direct methods
systems of linear algebraic equations can be solved either by direct
methods or by iterative methods. For system of moderate size, the use
of direct methods is often advantageous.
- distribution of population at age x C(x)
is the ratio of the population of age x, x+n to total population
- divorce
is a final dissolution of a marriage, that is, that separation of husband and
wife which confers on the parties the right to remarriage under civil,
religious and/or other provisions, according to the laws of each country.
- dizigotics twins
are due to the simultaneous fertilization of two or more ova and the
resulting children may be different sexes.
- Dwelling unit
is a statistical abstraction denoting housing accomodation appropriate for
occupation by one household.
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Demographical and statistical terms Symbols
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* E *
- elderly population
persons above the old age, term frequently used to define the period of life
during which most persons are retired
- endemic disease
is one that permanently affects substantial segments of a population,
in contrast with an epidemic, which spreads and then disappears within
a fairly short time; when it appears in a large number of countries, it is
called pandemic.
- expectation of life at age x e(x) or E(x)
it is the average number of years of life for males and females if they
continued to be subject to the same mortality experienced in the year (s)
to which these life expectancies refer.
- expectation of life at birth e(0) of E(0)
represents the mean length of life of individuals who have been subjected
since birth to the mortality of the considered life-table
- estended family
is one in which contains families within primary family. Son, daughters or
other relatives of the head who reside, with their own spouse and/or children,
in the household.
These "families within families" often are called "sub-families".
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Demographical and statistical terms Symbols
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* F *
- family
consists of two or more persons related to each other by blood, marriage, or
adoption. A residential family is one that occupies a housing unit as living
quarters. In such a case, the household head is also the head of the family.
The collectivity of related persons in sometimes called a "primary" family.
- family demography
concerns itself with the structure of families and household (i.e.,their size,
composition, and distribution) and the family-related events such as marriage
and divorce, that alter this structure through their number, timing and
sequencing.
- family life cycle
this term is frequently used to describe a sequence of life events from birth to
death, though its more precise meaning refers to a sequence of parenthood
stages over the life course, from birth of the children through their departure
from the home to their own childbearing .
- fecundity
is a measure of the maximum number of children which a woman is
physically capable of producing, or the capacity of a men , a women or a
couple to produce a live child.
- female fertility rates
are fertility rates (see) calculated for groups of women.
- fertility
is a measure which refers to the number of children borne by a woman.
- fertility histories
are accounts obtained for individual women of the important events in their
reproductive lives, such as marriage, pregnancy, births, infant deaths, etc.and
their dates. Fertility histories are often obtained retrospectively from survey.
- fertility lifetime
is the cumulative fertility until the date when all members of the cohort have
reached the end of the reproductive period.
- fertility rate
is a rate calculated by relating the number of live births observed in a population
or sub-population during a given period to a group of individuals of the same sex
in the riproductive ages. The denominator is commonly the mid-year population
in the stated period, but it may also be the number of years lived by the group
during the period, or the mean size of the group.
- foetal death
is death prior to the complete expulsion or extraction from its mother of a product
of conception , irrespective of the duration of pregnancy; the death is indicated by
the fact that after such separation the foetus does not breathe or show any other
evidence of life, such as beating of the heart, pulsation of the umbelical cord,
or definite movement of voluntary muscles. Late foetal deaths are those of twenty-
eight or more completed weeks of gestation.
- force of mortality or instantaneous rate of mortality m (x)
see " instantaneous death rate".
- forward survival
procedure for estimating the age distribution at some later date by projecting
forward an observed age distribution. The procedure uses survival ratios, often
obtained from model life table. The procedure is basically a form of population
projection without the introduction of new entrants (births) to the population.
- fraction of the last interval of age lived h(x) or H(x)
represents the part of the last year lived by those who die at each age.
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Demographical and statistical terms Symbols
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* G *
- general fertility rate
ratio of the number of live births in a perio d to the number of person-years
lived by women of childbearing ages during the period.
- generation
has been given a precise meaning and refers to a group of persons born
within a specified period of time, generally taken as a calendar year.
- gross reproduction rate (female) GRR
is computed similarly to net reproduction rate, on the assumption that
mortality before the end of the reproductive age is zero.
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Demographical and statistical terms Symbols
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* H *
- household
consists of persons who reside together , i.e., occupy a housing unity as
living quarters. Each household has a head, who usually is the chief
breadwinner. Living quarters occupied by a single person is also a household.
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Demographical and statistical terms Symbols
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* I *
- infant mortality Q(0)
is the mortality of live born children who have not yet reached their first
birthday
- infant mortality rates
are the annual number of deaths of infants under one year of age per 1000
live births in the same year.
- infecundity
is the lack of the capacity of a men, a woman or a couple to produce a live
birth.
- instantaneous death rate m (x)
is the limit of the _{n}q_{x }values (or probability at age x of dying before reaching
age x+n) as n tends to zero
- intercensal estimates
relate to dates intermediate to two or more censuses, and take the results of
these censuses into account.
- iterative methods
Systems of linear algebraic equations can be solved either by direct methods
or by iterative.
Iterative methods are used primarily for solving large and complex problems
for which, because of storage and arithmetic requirements, it would not be
feasible or it would be less efficient to solve by a direct method.
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Demographical and statistical terms Symbols
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* J *
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Demographical and statistical terms Symbols
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* K *
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Demographical and statistical terms Symbols
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* L *
- late foetal deaths
are foetal deaths of 28 or more completed weeks of gestation. Foetal deaths
of unknown gestational age are included with those 28 or more weeks.
- late foetal-death ratios
are the annual number of late foetal-deaths per 1000 live births in the me year.
- legal abortion
when the abortion occurs in conformity with the laws of certain countries.
- legitimate birth
may be defined as one whose father and mother were married to one another
at the time of conception. An illegitimate child or child born out wedlock
may be legitimized or legitimated by the subsequent marriage of its parents.
- legitimate birth rates
are calculated with legitimate births in the numerator and the currently
married female population in the denominator.
- life table
describes the course of mortality throughout the life cicle. Genarally a life
table contains: the death rate among persons of a given age x; the probability
of dying within a given age interval; the number of survivors to a specific age
from an assumed initial number of births; the number of years lived
collectively by those survivors within the given age interval; the person years
lived by a hypothetical cohort from age x on onward; and the expectation of
life of an individual of given age.
- life table survival ratios
these ratios are derived from the L _{x } column (stationary population) of the
life table. They are simply the ratio of the number of persons in the
stationary population that would be alive at a certain age to the number
of persons alive at an earlier age.
- life-time abortion rate
is the sum of age-specific abortion rates and is a synthtic measure of abortion
per woman or per 1000 women.
- live birth
is the complete expulsion or extraction from its mother of a product of conception,
irrespective of the duration of pregnancy, which after such separation breathes
or shows any other evidence of life such as beating of the heart, pulsation of the
umbilical cord, or definite movement of voluntary muscles, whether or not the
umbilical cord has been cut or the placente is attached; each product of such a
birth is considered live-born regardless of gestational age.
- logistic population
is a population growing in accordance with the logistic law of growth,
ie., a population in which the growth rate decreases as a linear function
of the population already alive and which will tend asymptotically to an
upper limit.
- long-term emigrants
are residents or persons who have resided continuosly in the country for
more than one year, who are departing to take up residence abroad for
more than one year.
- logit of the probability of dying LN[q(x)/p(x)]
is given by the logarithm of the rate between the probability of dying before
reaching age x and the probability of surviving at age x. See also the
meaning of symbols q(x) and p(x) under the letter P.
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Demographical and statistical terms Symbols
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* M *
- marriage
is the act, ceremony or process by which the relationship of husband and wife
is constituted. The legality of the union may be established by civil, religious,
or other means as recognized by the laws of each country.
- maternal mortality
according to ninth revision of the International Classifications of Diseases,
"maternal death" is defined as the death af a woman while pregnant or within
42 days of termination of pregnancy, from any cause related to or aggravated
by the pregnancy or its management but not from accidental or incidental
causes.
- maternal mortality rates
are the annual number of maternal deaths divided by the live births in the same
year.
- maternity
is used to denote a confinement resulting in the birth of one or more children.
- maximum resistance value at age xm r(xm) or R(xm)
represents the maximum value which the function (or distribution) of
resistance reached at age xm.
- mean age of a population MAP
is the average age of all its members
- median age of a population MDP
is the age which divides the population into two numerically equal groups
- mean age of childbearing
represents the mean age of the mothers at childbirth
- median length of life P o
is the age at which half the original cohort of births have died
- mid-year population estimate
refer to the de facto population on 1 july, or to the mean of two year-end
official estimates.
- migrant
an individual whose place of residence differs at the beginning and the
end of a certain interval of time.
- migration
the movement of people across a specified boundary for the purpose of
establishing a new permanent residence. Divided into international
migration (migration between countries) and internal migration (migration
with a country).
- model life table
is a life table which is based only upon the generalization of empirical
relationships derived from a group of observed life tables.
- monozigotic twins
occur when one ovum splits after fertilization; the resulting children must
always be the same sex.
- mortality rate at age x (see Central death rate at age x) _{n }m _{x };_{ n }M_{ x}
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Demographical and statistical terms Symbols
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* N *
- natural fertility
age pattern of marital fertility observed in non-contraceptive populations
where reproductive behavior is not affected by the number of children
already born.
- natural family planning methods
this term has been applied collectively to cover the rhythm method, the basal
body temperature method, and other techniques which attempt to identify
stages of the woman’s ovulatory cycle.
- natural increase
number of births minus number of deaths during a year or other span of time.
In some cases, it may be negative.
- neonatal mortality rate
annual number of deaths to infants under 28 days of life per 100000 live
births during the year.
- net reproduction rate (female) R(o)
is defined as the average number of live daughters that could be born to a
hypotetical female cohort which would be subjected to a set of current
age-specific fertility and mortality rates
- nuclear family
a nuclear family is one consisting of a couple and their children, if any.
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Demographical and statistical terms Symbols
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* O *
- open population
an open population is one where migration is a significant component of
population change, either in size or composition, or both.
- order-specific total fertility rate
is given by the summation of age-specific fertility rates order by order.
- order-specific fertility rate
number of live births of a given birth order (1,2,3, and so on) occurring in
a year, per 1000 women in the childbearing ages
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Demographical and statistical terms Symbols
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* P *
- parity
women are also classified by parity usually on the basis of the number of
children born alive. A woman who has not borne any live children is called
a zero-parity woman. a one-parity woman has borne one child but no more,
and so on.
- parity progression ratios
are fractions whose denominator is the number of women with n children,
and whose numerator is the number of women with n+1 children .
- parity-specific birth probabilities
the numerator consists of the number of order x+1 occurring during a period,
and the denominator consists of the number of women of parity x at the
beginning of the same period.
- perinatal mortality ratios
are the annual number of late foetal deaths plus infant deaths within the first
week of life per 1000 live births in the same year.
- perinatal period
is the period defined from the 28 ^{th} weeek of gestation to the seventh day of
life, or also from the 20 ^{th} week of gestation to the 28 ^{th} day of life. .
- periodic abstinence
when coitus is avoided during the period when the woman is believed to be
fecund and takes place only during the so-called safe period of the menstrual
cycle.
- population censuses
are taken to obtain information about the state of the population at a given
time.
- population forecast
is a projection in which the assumptions are considered to yield a realistic
picture of the probable future development of a population.
- population momentum
is the tendency for population growth to continue beyond the time that
replacement-level fertility has been achieved because of the large and
increasing size of cohorts of childbearing age and younger, resulting from
higher fertility and/or falling mortality in preceding years.
- population projections
are calculations which 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.
- population pyramid
represents graphically a population’s age distribution as a histogram.
That histogram shows the population by age and sex and is so named
because of its pyramid shape.
- premature birth
is a pregnancy ending before the normal period of gestation.
- primary sterility
when the woman has never been able to have children.
- probability of dying between age zero and x q(x) or Q(x)
represents the probability that an individual at birth will die before exact
age x
- probability at age x of dying before reaching age x+n _{n}q_{x}
represents the probability that an individual of exact age x will die before
exact age x+n
- probability of surviving from birth to age x p(x) or P(x)
is the complement to one of the probabilities of dying between age zero
and x
- probability at age x of surviving before reaching age x+n _{n }p_{ x}
is the complement to one of the probabilities of dying between age x and
x+n
- probable length of life (see Median length of life)
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Demographical and statistical terms Symbols
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* Q *
- quasi stable population
is a formerly stable population with constant fertility and gradually
changing mortality.
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Demographical and statistical terms Symbols
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* R *
- rate computation
the crude birth, death, marriage, divorce etc. are generally the annual number
of each of these vital per 1000 mid-year population.
- rate of population growth r or TA
the increase or decrease of a population in a period divided by the number of
person-years lived by the population during the same period.
- rate of natural increase at time t, or b(t)-d(t) n(t)
the difference between the births and deaths occurring during by the number
of person-years lived by the population during the same period. This rate,
which specifically excludes changes resulting from migration, is the difference
between the crude birth rate and the crude death rate.
- replacement-level fertility
the level of fertility at which a cohort of women on the average are having only
enough daughters to replace themselves in the population.
By definition, replacement level is equal to a net reproduction rate of 1.0. The
total fertility rate is also used to indicate replacement-level fertility.
Generally, in industrialized countries, a TFR (total fertility rate) of 2.1 is
considered to be replacement level.
- reproductive histories
are accounts obtained for individual women of the important events in their
reproductive lives, such as marriages, pregnancies, births, infant deaths, etc.,
and their dates. Reproductive histories are often obtained retrospectively from
surveys.
- resistance function r(x)
is the mathematical expression of the resistance data computed on the life-table.
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Demographical and statistical terms Symbols
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* S *
- sex ratio
is the ratio between males and females (or vice versa) of a population.
- sex ratio at birth
is the ratio between male births and female births (or vice versa) of a observed
population.
- sex structure C(x)
of the population is measured by the ratio of the total number of one sex to the
total number of the population.
- short-term emigrants
are residents or persons who have resided continuosly in the country for more
than one year, who are departing to work outside the country for one year or less,
and their dependants including domestic employees.
- skewness of a fertility distribution IAS
represents the degree of asymmetry of a function or a curve of the age-specific rate
of fertility
- spontaneous abortion
abortion following a non-induced intra-uterine death, which may has occurred
some time before expulsion.
- stable population SP(x)
a population with an unchanging rate of growth and an unchanging age
composition, because age-specific birth and death rates have remained
constant over a sufficient period of time.
- standardized birth rates
to compare the fertility of different populations, standardized birth rates are
often used to eliminate the effect on the birth-rate of certain differences in
structure of the population (most commonly the age and sex structure).
- stationary population L(x) or _{n} L _{x}
number of person-years lived between age x and x+n by an original cohort of
100,000 for a population with 100,000 annual births and deaths, or stable
population in which the intrinsic rate of natural increase is zero.
- sterility
is so called the lack of the capacity of a men, a woman or a couple to produce
a live child. Among women we distinguish primary sterility where the women
ha never been able to have children, and a secundary sterility, which arise after
one or more children have been born
- survival rates _{h} SR _{x }
survival rates are calculated from the stationary population as the ratio of the
number of survivors in an age interval to the number in the preceding interval.
- surviving function
is the mathematical expression of the survivors of a life-table.
- survivors l_{x }or S _{x}
number of survivors at age x out of an original cohort of 100,000 births.
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Demographical and statistical terms Symbols
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* T *
- total divorce rate
is the summation of the age-specific divorce rate and is defined for men or
women. This rate is an indicator of a synthetic cohort giving the total number
of divorces a men or a woman experiences on average throughout life based
on observed period rates.
- total numbers years T _{x }
is the number of person-years lived at age x and older
- total reproduction rate (or total fertility rate) TFR
is the summation of the series of age-specific fertility rates, or the average
number of children that would be born alive to a hypothetical cohort of
women if, throughout their reproductive years, the age-specific rates for the
specified year remained unchanged.
- true rate of natural increase
is equal to the difference between the intrinsic birth rate and the intrinsic death
rate.
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Demographical and statistical terms Symbols
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* U *
- urbanization
growth in the proportion of a population living in urban areas.
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Demographical and statistical terms Symbols
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* V *
- variance (empirical) DS
represents the variance computed on observed female age-specific fertility
rates
- variance (theoretical) VA
represents the variance computed by the fertility function
- value of maximum fertility rate at age FXM F(FXM)
is the maximum of observed or theoretical values of age-specific fertility
rates
- vital index
is the ratio of the number of births to the number of deaths during a period.
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Demographical and statistical terms Symbols
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* W *
- women years
is the number of years lived by a given number of women during a stated
period.
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Demographical and statistical terms Symbols
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* X *
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Demographical and statistical terms Symbols
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* Y *
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Demographical and statistical terms Symbols
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* Z *
- zero population growth
is a situation in which a population is in equilibrium, with a growth rate of
zero, achieved when births plus immigration equal deaths plus emigration.
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