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Denominators. Demography in epidemiology FETP India. Competency to be gained from this lecture. Use demographic methods and data in applied epidemiology . Key elements . Demography Sources of information Demographic processes. Demography . Definition

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Denominators l.jpg


Demography in epidemiologyFETP India

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Competency to be gained from this lecture

Use demographic methods and data in applied epidemiology

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Key elements

  • Demography

  • Sources of information

  • Demographic processes

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  • Definition

    • Study of the size and distribution of human populations

    • Study of processes that bring about changes in these populations

      • Fertility and mortality (Biological)

      • Migrations

  • Objective

    • Study trends over time and variation across regions or subgroups in population processes


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Factors affecting fertility and mortality

  • Proximate determinants

    • Ability to use contraception

  • Exogenous factors

    • Social, cultural, economic, psychological, environmental

    • Behavioural or life style factors

      • In some cases, access to or use of health services


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Consequences of change in population processes: Example of ageing

  • Labour force and the economy

  • Child bearing in the adolescent and older ages

  • Women’s and children’s health and well-being

  • Population movements

  • Epidemiology of diseases


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Sources of demographic data

  • Censuses

  • Vital registration systems

  • Sample surveys

  • Sample registration system (India)

Source of data

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Sample registration system (SRS) in India

  • 1964-5

    • Pilot basis

  • 1969-70

    • Full scale

  • Dual reporting system

  • Provides estimates of birth and death rates at state and national levels

    • Regular publication of annual vital rates


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SRS’ dual reporting system

  • Each event (birth or death) captured by two independent procedures

    • Continuous enumeration in population

    • Sample survey every 6 months

  • Events matched

    • Missing in both systems estimated

  • Evaluation of SRS

    • Under-enumeration does not exceed 5%


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Sample design for SRS

  • Rural areas

    • Each district divided in two strata

      • Villages > 1500 population

      • Villages < 1500 population

    • Simple random sampling of villages and segments from the two strata without replacement

  • Urban areas

    • Sampling unit: Census enumeration block


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Half yearly survey for SRS by full time supervisor from census directorate

  • Collects information on births and deaths from residents and visitors

  • Reference period:

    • Six month

    • 12 month to capture events missed during the last survey

  • Updates

    • House, household members and pregnant women list

  • Matching of events

  • Field verifications

    • Unmatched

    • Partially matched events


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Sources of information on causes of death

  • Urban areas

    • Under SRS

    • Collection of information on medically certified deaths

  • Rural areas

    • Collection of data by paramedical staff using verbal autopsy techniques


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Demographic processes

  • Number of people in an area at a given time:

    • Pt = Po + B - D +I -O

      • B= Births

      • D= Deaths

      • I= Immigrations

      • O= Out-migrations

  • From age structure to age composition


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Crude death rate


Age specific death rate


Infant mortality rate


Neonatal mortality rate


Post-neonatal mortality rate


Perinatal mortality rate

Expectation of life at age x


Cause-specific death rate


Maternal mortality rate

Rates and ratios of mortality and pregnancy wastage


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Age pyramid, India, 1961 and 2001

Influences risk of various illnesses and conditions as well as the health risk behaviours


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Causes of death

  • Study the process of mortality

  • Stratified for

    • Still birth

    • Neonatal deaths

    • Infant deaths

    • Child deaths

    • Maternal deaths

    • Adult deaths


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Determinants of mortality

  • Demographic factors

    • Age, sex, marital status and family size

  • Socio-economic variables

    • E.g., Income, education, religion

  • Health related behaviours

    • E.g., Smoking, alcohol and drug use

  • Disabilities and diseases

  • Type of death

    • Still birth, neonatal, infant, child, maternal and adult


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Cause of death by verbal autopsy among > 5 years of age, Tamil Nadu, India, 2004(ICD 10)


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Life tables

  • Study longevity, success rates and hazards

  • Ordinary life tables

    • Studies attrition from a cohort resulting from a single factor

  • Multiple decrement life tables

    • Attrition due to more than one factor

  • Multi-state life tables

    • Move through different states


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Cause elimination using life tables

  • Objective

    • To eliminate the effects of competing risks of dying from various causes on the risk of dying from a given cause

    • To measure the ‘pure’ severity of the cause

  • Example

    • To study the mortality of HBV infection acquired at birth, one has to subtract, year by year, the mortality from other causes since there is a long delay between infection (at birth) and death (during adulthood)

  • Method

    • Construct life table in which all causes are eliminated except one particular cause


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Population distribution: Size and density of the population by geographic subdivision

  • GIS (Geographic information system)

    • Organized collection of computer hardware, software, geographic data and personnel designed to efficiently capture, store, update, manipulate, analyze and display all forms of geographically referenced information

  • Useful to study trends and spatial pattern of population processes

  • Provide insights into the location and distribution of public health needs and resources


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Fecundity and fertility

  • Frequency of live births in a population

  • Fecundity

    • Ability to produce live offspring

    • Cannot be measured

    • Can be assessed clinically

  • Fertility

    • Actual production of live offspring


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Crude birth rate


General fertility rate


Age-specific fertility rate


Total fertility rate


Gross reproduction rate


Not reproductive rate


Parity progression ratio


Mean birth Interval

Measures of fertility


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Determinants of fertility

  • Focus on proximate determinants

  • Include

    • Exposure to sexual intercourse

    • Exposure to conception

    • Gestation and successful parturition


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  • Conventional

  • Permanent

  • Abortion to unwanted pregnancies

  • Failure


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Adolescent pregnancies

  • May cause sexually related problems including sexually transmitted diseases

  • Induced abortion

  • Improper child development

  • High mortality risk for mother and babies


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  • Definition

    • Movement of people from usual (primary) residence to another

    • Involves crossing an administrative or political boundary

  • Most difficult to measure


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Nuptiality: Marriage and marital dissolution

  • Frequency of marriages

  • Characteristics of persons joining

  • Dissolution

    • Separation

    • Divorce

    • Death

  • Crude marriage rate

  • Age and sex specific marriage rate

  • General marriage rate

  • Median or mean age at marriage


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Estimations and projections on the basis of census data

  • Inter-censal

  • Post-censal

  • Future (Projection)


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Take home messages

  • Demography is closely related to epidemiology

  • Sources of information are diverse and cross validate each other

  • Demographic processes are studied by time, place and person

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