Sources Of Data: • Demographic Data Cover: • Demographic Events Include

SOURCES OF DATA • Demographic data cover: – Demographic processes and events

• Demographic events include: – Births, deaths, marriages, and divorce – Sex, age, marital status, birthplace, occupation and education

• Main sources of demographic data: 1. Census 2. Vital statistics 3. population surveys 1

Census • A census is a national enumeration of the population at one point in time • Censuses are: – Expensive to undertake – takes years to plan – Involve a large staff of field workers – Takes years to compile and publish the results

• Aim of censuses – to establish size, distribution and composition of the population 2

Innovations and the census • • • • • •

Virtual census CD Rom Geographical information systems Other geographic based mapping Statistical software – SPSS, SAS, PC-Edit Internet – Have made census data accessible and versatile 3

Main purposes of the census • To determine electoral arrangements on the basis of population • To provide baseline data for planning and administration – Numbers and characteristics of people are important in planning – monitoring the demand for schools, housing, and health services, assessing the impact of changes in the labour force and immigration, undertaking market analysis of the demand determining appropriate location for public amenities and shopping centers 4

Census • The census is also the chief source of information on small areas and small groups • Two types of census: – De facto census- counts everyone at the time – De Jure – counts people where they usually live

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Limits of the Census • Accuracy – info from self completed form or short interview • Privacy – content limited by considerations of privacy laws – Prohibits intrusive questioning – eg details of personal wealth, census files cannot be linked to other databases, no crosstabulations at the small area level • Immediacy • Coverage 6

Other Sources of Data • Vital statistics System – It collects information on individuals when they experience the vital events – births, marriage, or death

• Information collected can be quite extensive – statistics on births include details about the new born (sex, place of birth), mother (age, birthplace, marital status and occupation). 7

Surveys and Statistical Information Surveys • Surveys supplement censuses and vital statistics • Surveys have become an increasingly important source of data Statistical Information • Statistical agencies in different countries publish statistics information such as Social Trends, Statistical Abstracts, National Year Books 8

Data Quality • Data coverage • Data quality • Examples of concerns about data coverage and quality: – Children born at home and died in infancy are often not enumerated or registered – Marriage – the omission of consensual or de facto unions – Migration or uncontrolled movement across borders – Survey figures are subject to error too – findings may not be representative of the general population 9

Cross-national data • For comparative studies there are many major sources: – UN Demographic Yearbook – coverage on population growth, birth and death rates, age composition, urban and rural populations. Most volumes contain extra info on fertility, mortality and migration and census statistics. – Population Trends and Prospects contain statistics on population numbers, growth rates, birth and death rates, life expectancy and other key indicators. Projections have 3 ‘variants’ – high, medium and low. 10

Cross-national data • Age and Sex Distribution of World Populations – Contain age structure data for countries, world regions over the same period

• World Bank’s World Development Report • WHO’s World Health Statistics Annual • Eurostat’s Demographic Statistics 11

Components of Change • Data needed to study demographic transition and trends through time: – Births – Deaths – Census data on population totals

• Natural increase: the difference between numbers of births and deaths • Net migration = the difference between arrivals and departures 12

Components of Change • Population growth = natural increase plus net migration • Or • Population growth = (births – deaths) + (arrivals –departures)

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Population growth • It is the difference between population totals at two dates P2 – P1 = Population growth – Where P1 is the initial population P2 is the end of the period – population

P2-P1 = (births – deaths) + (arrivals – departures) P2 = P1 + (births – deaths) + (arrivals – departures) The demographic balancing equation refers to total numbers, rather than changes in growth rates 14

Population growth • Total numbers are important for planning for the provisions of goods and services depends on the number of customers or service users • To compare populations in different times and places, rates and percentages are used to show the relative pace, relative size of changes in different population totals 15

Comparative Measures • Demographic rates – Rates are the most frequently used comparative measures of population change – Demographic rate show the relationship between the number of demographic events (numerator) and the population at risk (denominator) – Population at risk is the population that could experience a particular event (giving birth or migrating at a particular point in time). 16

Demographic rates • The most convenient approximation to the population at risk is the total population at mid-year. • Mid year is assumed to be the point by which half the changes have occurred. • When unavailable in published statistics, the mid-year population may be calculated as the mean or average of the population at the start and end of the year. 17

Mid-year population • Example of calculating the mid-year population – If the population on January 1 was 20,000 and on 31st December 40,000, each total would produce very different rate (P2 + P1)/2 = (20,000 + 40,000)/2 = 30,000 Rates are usually multiplied by 100 or 1000 to produce figures greater than 1. 18

Other types of measures • When the population at risk is unavailable, a ratio is used. • It expresses the size of a number relative to another convenient number • Eg sex ratio – ((males/females) x 100)

• Denominators are selected according to the availability of data and ease of understanding 19

Comparative measures • Also used in comparative studies are proportions and percentages. • A proportion is a ratio in which the denominator includes the numerator. Proportions are part of one whole ie fractions – ratio are often multiplied by 100 to produce percentages

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Comparative measures • Probability another comparative measure ranges between 0 and 1. A probability is the ratio of events in a fixed period of time to the initial population at risk. • In demography probabilities are always based on the initial population

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Comparative Measures • Probability example – The probability of dying at age 80 is based on the number of people who celebrated their 80th birthday (initial population) – If 2000 women reached their 80th birthday and 800 of them died before reaching 81, their probability of dying at age 80 is :

800/2000 = 0.4 22

Basic measures of change Crude birth and death rates – These are basic measures of population change used in assessing population growth – CDR and CBR are based on the total population growth and its components – They are called crude because they are unrefined with regards to the population at risk – These measures are used in the DT allowing countries to be compared 23

Basic measures of change • CBR = number of live births in a year x 1000 mid-year population • CDR = number of deaths in a year x 1000 mid-year population

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Basic measures of change Factors that affect their calculation and interpretation: – Crude rates ignore sub-groups – eg in LDCs more deaths in 0-1 age category – Crude rates are calculated for calendar years – Age structure can have substantial effect on crude rates. Eg in LDCs have high proportion of young people and therefore low crude death rates – Standardization techniques are employed to remove the influence of age structure 25

Rates of natural increase and net migration • From CDR and CBR is derived the (crude) rate of natural increase (RNI). It is the difference between them • RNI = CBR – CDR • Or • Rate of natural increase = births – deaths in a year x k Mid-year population 26

Rate of and net migration • Where international migration is not important, natural increase is the only source of growth • Most Polynesian and some Micronesian countries are affected by migration • At sub-national level, net migration is often the major component of population change, - shown in growth and decline of villages, rural settlements, cities, suburbs and towns • Rate of net Migration is based on mid-year population • RNM = net migration x k • Mid-Year population • k = 1000 or 100 27