SOURCES OF DATA

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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

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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

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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

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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

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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

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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).

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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

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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

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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.

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Cross-national data

• Age and Sex Distribution of World Populations
• Contain age structure data for countries, world
  regions over the same period
• World Banks World Development Report
• WHOs World Health Statistics Annual
• Eurostats Demographic Statistics

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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

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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

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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

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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).

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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.

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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.

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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

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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

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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

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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

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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

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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