Sources of population data  (1)censuses  (2) sample surveys

 (3) registration of migration and vital events such as births, deaths, marriages, and divorces.

• Censuses consist of an enumeration of the population in a given area at a given time. • Sample surveys may be made to obtain information about certain groups, such as school-age children, or

to obtain information about all the population on a sample basis.

• Questions

may

be

asked

concerning

certain

characteristics of each person (age, sex, marital condition, etc.) at the same time that the count is made.

• Censuses and sample surveys usually provide a picture of the population at a given time.

• The occurrences most commonly registered are births,

deaths,

marriages,

divorces,

and

international migratory movements. • In these registers are recorded the name, address,

and some data on the characteristics of each individual in the population. • In countries having population registers, generally every person is registered at birth in this community of residence.

• If he moves to another community, an official transcript of his birth and his current civil and family status is sent to his new community. • Among modern nations they have been established in

recent years for such administrative purposes as food rationing, housing rationing, settlement

programs, etc.

• It seems that the quantity of administrative detail and

office work required for recording each change of residence and status in modern mobile population involves too much expenditure of time and effort for population registers to be maintained for purely statistical purposes.

Age ratios •

An age ratio compares there two numbers by dividing the

reported number of persons in the age group by the number “expected” on the basis of the number of persons reported in each of the adjacent age groups.The age ratio per100 females

aged 25 to 29, for example , is arrived at as follows: Age ratio female 25-29

=1 2

=

𝑓𝑒𝑚𝑎𝑙𝑒𝑠 25−29 (𝑓𝑒𝑚𝑎𝑙𝑒𝑠 20−24+𝑓𝑒𝑚𝑎𝑙𝑒𝑠 30−34)

×100

200×𝑓𝑒𝑚𝑎𝑙𝑒𝑠 25−29 (𝑓𝑒𝑚𝑎𝑙𝑒𝑠 20−24+𝑓𝑒𝑚𝑎𝑙𝑒𝑠 30−34)

• According to the 1960 data for Sweden, in table 2A the age ratio for females 25-29 would be200×215,572 230,406+233,828

=92.9

• Age ratios can be calculate for each age group (provided the intervals are equal) except the youngest and the oldest .

• Persons for whom no age is reported often have been included in the tabulations by age in a special “age

unknown” class.

• Some countries make it a practice to assign ages to

individuals of unreported age, taking into account their other characteristics and characteristics of other members of their households. • In that case, the unknowns are either (a) eliminate from the distribution before calculated percentages,

or (b)distributed proportionally among the known ages.

AGE-SEX PYRAMID • Population pyramid can be defined as a pictorial representation of age and sex distribution of a population. One of the best ways to illustrate the population structure and composition of any country or

population is to draw her population pyramid. Population pyramid represent the age and sex

composition and structure of any country. • Basically, an age-sex pyramid is a bar chart in which all the bars taken together represent 100 percent of the population.

MORTALITY Measure of mortality are – 1) Death rates

2) Crude death rate 3) Specific death rates

4) Infant mortality rates

Life tables • A life table population is the population which would

exist if the age-specific death rates prevailing at some particular time were to continue throughout the

life span of all the individuals, with no change in the number of births each year and no migration. •

It is constructed to show what the effects of mortality on a population would be if it were not being affected also by fertility and migration.

• The expectation of life at various ages and the survival ratios which may be determined, in a single

step, form the survivors in each year of age or age group, are life table values of great use to

demographers. • Complete life tables show all of the life table functions discussed below by single years of age.

• Abridged life tables usually give the life table

functions by 5-year age groups; some tables show life table functions for certain selected single years of age. • Life tables are usually prepared from mortality rates based on vital statistics (for the number of deaths by age and sex) and census data (for the population by age and sex).

The uses of life tables are (1) Life table is used to project future population on the

basis of the present death rate. (2) It helps in determining the average expectation of

life based on age specific death rates. (3) The method of constructing a life table can be followed to estimate the cause of specific death rates, male and female death rates, etc.

(4)

The survival rates in a life table can be used to

calculate the net migration rate on the basis of age distribution at 5 or 10 year interval. (5) Life tables can be used to compare population trends at national and international levels.

Notation of life tables Notation

Definition

x, x+n

Age interval or period of life between two exact ages stated in years. Proportion of persons alive at the beginning of the age interval who die during the age interval.

𝑛𝑞𝑥 𝑙𝑥

Of the starting number of newborns in the life table (usually 100000) the number living at the beginning of the age interval.

𝑛 𝑑𝑥

The number of persons in the cohort who die in the age interval (x,x+n). Number of years of life lived by the cohort within the indicated age interval. Total person year of life contributed by the cohort often attaining age x. Average number of years of life remaining for a person alive at the beginning of age interval.

𝑛𝑙𝑥

𝑇𝑥 𝑒𝑥0

Nature of life tables nqx =

𝑛𝑑𝑥 𝑙𝑥

For new babies (or) “0”,

𝐿0 = 0.3𝑙0 +0.7𝑙1 For 1-4 age group, 𝐿1 = 4(0.5𝑙1 +0.5𝑙5 )

For other age group,

𝑛𝐿𝑥 =

𝑙𝑥 +𝑙𝑥+𝑛 n[ ] 2

𝑇𝑥 = σ 𝑛𝐿𝑥

𝑇𝑥+𝑛 = 𝑇𝑥 -𝑛𝐿𝑥 𝑇𝑥 0 𝑒𝑥 = 𝑙 𝑥

Example Complete the cells in the following table for the population that is the source for male in an

area of a

country. Age

𝑛𝑞 𝑥

65-69

0.17320

70-74

0.25862

75-79

0.37529

80-84

0.52397

85+

1.00000

𝑙𝑥

𝑛𝑑 𝑥

60158

10968

𝑛𝐿 𝑥

𝑇𝑥

𝑒𝑥0

FETILITY Measure of Fertility are 1) Crude Birth Rate (CBR) 2) General Fertility Rate (GFR) 3) Age-specific Birth Rate (ASBR) 4) Parity-specific Birth Rate 5) Gross Reproduction Rate (GRR) 6) Net Reproduction Rate (NRR) 7) Child-woman Ratio (CWR)

• Fertility concerns the addition of new members to a population by birth; that is, the actual performance of a population in bearing children. It is not to be confused with fecundity, the biological capacity of the population to bear children. • Fertility, mortality, and migration are the three processes which may act to change the size or composition of a population.