Using Data for Demographic Analysis

Country Course on Analysis and Dissemination of Population and Housing Census Data with Gender

Concern24-28 October 2011, Jakarta, Indonesia

Demographic statistics are the data to the size, growth, characteristics and distribution of population, and to their dynamics of fertility, mortality and migration.

Most academics, planners and policy makers use population data to improve the understanding of human society.

Population is the total number of human beings inhabiting a country, town or area at a given period of time at a moment.

-Population in a period of time: de-jure Population

-Population at a moment: de facto population

Generally refers to the absolute number of population.

(e.g: The total Population in Colombo District is 2,234,246 per cent of total population of Sri Lanka in 2001).

Population change refers to a increase or a decrease of population at time.

Population change not only implies the change in its size but also in its internal composition and structure with respect to its various characteristics and spatial distribution.

The size of the population in any area increase through birth and immigration (or in-migration) and decreases through deaths and emigration (out migration).

The most basic method of calculating of population change over time is the “balancing equation technique”.

Where pn = Population at the later date; Po = Population at the earlier date B = Births; D = Deaths; I = Immigration (in-migration); and E = emigration (or out –migration) between the two dates.

Pn = Po + (B-D) + (I- E)

Population per unit of land area; for example persons per square kilometer, or persons per kilometer of arable land.

Population Density = Total population in an a given year

Square mile of Land area

Population Distribution: The patterns of settlement and dispersal of

a population.Population distribution refers not only for spatial distribution of population but also for its socio-economic categories, such as urban – rural, age and sex ect.

Population composition refers to the characteristics of population.

Ascribed composition; age, sex, race and ethnicity

Achieved composition; education, occupation, industry ect.

Age and Sex composition: Age and sex are the most basic characteristics of a population. Every population has a different age and sex composition, i.e the number or proportion of males and females in each age group.

The ratio of the economically dependent part of the population to the productive part; arbitrarily defined as the ratio of persons in the “dependant” (under 15 and over 64 years of age) to those in the “economically productive ages” (15-59 or 15-64 years of age) in a population.

Total dependency ratio = Population <15 + Population >65

Population 15 -64

Child dependency = Population <15Population 15- 64

Old (aged) dependency = Population >64Population 15 -64

A special type of bar chart that shows the distribution by age and sex.

Most countries fall into one of three general types of pyramids:

(1) Expansive – a broad base, indicating a high proportion of children and a rapid rate of population growth;

(2) Constrictive – a base is narrow than the middle of the pyramid (smaller number of people in the younger ages usually due to a recent rapid decline in fertility)

and

(3) Stationary – a narrow base and roughly equal numbers in each age group, tapering off gradually at the older ages.

The factors, which determine the size, growth, distribution and composition of population.

They are : 1. Fertility 2. Mortality

3. Migration Fertility–The actual number of live births per woman who

are in the reproductive ages.

Mortality –The study of deaths in a population

Migration - The movement of people across a specified boundary for the purpose of establishing a new or permanent residence.

- Internal Migration (migration within a country)- External or International migration ( migration between

countries)

Life Expectancy:

an average number of additional years a person can expect to live if current mortality trends were to continue. This derives from a life table (A tabular display of life expectancy and the probability of dying at each age for a given population, according to the age – specific death rate prevailing at that time.

The life table provides an organized, complete picture of a population’s mortality.

Life expectancy at birth is the average number of year a newborn infant can expect to live current mortality trends were to continue.

Uses of demographic Measures

Study the demographic characteristics (composition & behaviour at a given period or point of time

Asses the changes of demographic process at different period of time within the same population

Compare and contrast the demographic processes occurring in different populations within the same period of time

Make projection & forecast (estimate) the future Population

Basic Measures Absolute and relative numbers

Most demographic data present in terms of absolute numbers. Eg., Population size, Number of births, Number of deaths etc…

For some purposes these absolute numbers are using in the demographic analysis

Relative numbers derive by relating absolute number of event to the absolute number of persons in the population (e.g. – CBR, Sex ratio)

Contd.

Relative numbers are in different forms

1. Proportions & percentages2. Ratios3. Rates4. Probabilities

1. Proportions and percentages

Proportion is a number in a particular group relative to the total number. In brief it expresses the relationship of a sub group in a population to the entire population.

eg. – Proportion of Sinhalese population

E.g .- Proportion of males = #Males/ Total population

o Proportion has the form: P = A/B where A is the numerator which is a subset (part) of the denominator of B. e.g. proportion of unemployed divided by the total population in that country.

o The sum of all proportions that can be derived from the common base is unity. E.g.- proportion of ever married and proportion of never married = 1. So proportion takes the value between 0 and 1.

o Percentage is another way of expressing the relationship of a part of the whole. The proportion is commonly expressed as 100 base called percentage.

2. Ratio

A ratio is a single term to indicate the relative size of two sub groups of population. E.g.- sex ratio (M/F); indicates the relative size of the male population compared with the female population in a country for a particular year.

In mathematics the ratio of two numbers is called quotient. E.g.- 1:12 or 1/12– a inches to 12 inches or feet.

Ratio has the form of Ratio = A/B; where A is one number or one group B is another number or group of population.

So we can express a ratio as – so many A per unit of B.

Different form of ratios:

i. The numerator (A) and denominator belong different set or universe. How much A is larger than B? e.g. Population of Asia 4.38 times the population of Europe. A & B derive from different sources.

ii. A & B belong to the same universe – e.g. Sex ratio

iii. Proportion : ratio of two numbers from the same universe but it is a distinct category as A/A+b Numerator included in denominator; Proportion of married = married15+/ married 15+ unmarried 15+

iv. More complex ratio: A &B from hypothetical universe e.g. survival ratio

3. Rates

The relationship between the event and the exposure at risk

population in the same point. In other words how frequently a

demographic event is occurring in relation to a population at risk

during a specified period of time.

E.g.- CBR, CDR, IMR, MMR etc.

Rates are of different types.

• Crude rates• Specific rates• General rates• Refined rates• Cohort rates

4. Probability

When an event occurs in a population then the likelihood of occurrence of that event within a given interval of time.

E.g. probability of dying