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 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

Demography

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

Demography

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

Demography

Sources of demographic data

• Censuses • Vital registration systems• Sample surveys • Sample registration system (India)

Source of data

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

Demography

SRS’ dual reporting system

• Each event (birth or death) captured by two independent procedures1. Continuous enumeration in population2. Sample survey every 6 months

• Events matched Missing in both systems estimated

• Evaluation of SRS Under-enumeration does not exceed 5%

Demography

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

Demography

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

Demography

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

Demography

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

Processes

Rates and ratios of mortality and pregnancy wastage

• CDR Crude death rate

• ASDR Age specific death

rate

• IMR Infant mortality rate

• NMR Neonatal mortality

rate

• PNMR Post-neonatal mortality

rate

• PMR Perinatal mortality rate

• Expectation of life at age x

• CSDR Cause-specific death

rate

• MMR Maternal mortality rate

Processes

Year 1961

Male Female70 +

65-69

60-64

55-59

50-54

45-49

40-44

35-39

30-34

25-29

20-24

15-19

10-14

5-9

0-4

Year 2001

Male Female70 +

65-99

60-64

55-59

50-54

45-49

40-44

35-39

30-34

25-29

20-24

15-19

10-14

5-9

0-4

Age pyramid, India, 1961 and 2001

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

Processes

Causes of death

• Study the process of mortality• Stratified for

Still birth Neonatal deaths Infant deaths Child deaths Maternal deaths Adult deaths

Processes

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

Processes

Cause of death by verbal autopsy among > 5 years of age, Tamil

Nadu, India, 2004(ICD 10)

Processes

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

Processes

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

Processes

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

Processes

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

Processes

Measures of fertility

• CBR Crude birth rate

• GFR General fertility rate

• ASFR Age-specific fertility

rate

• TFR Total fertility rate

• GRR Gross reproduction

rate

• NRR Not reproductive rate

• PPR Parity progression

ratio

• MBI Mean birth Interval

Processes

Determinants of fertility

• Focus on proximate determinants• Include

Exposure to sexual intercourse Exposure to conception Gestation and successful parturition

Processes

Contraception

• Conventional • Permanent• Abortion to unwanted pregnancies• Failure

Processes

Adolescent pregnancies

• May cause sexually related problems including sexually transmitted diseases

• Induced abortion• Improper child development• High mortality risk for mother and

babies

Processes

Migration

• Definition Movement of people from usual (primary)

residence to another Involves crossing an administrative or

political boundary

• Most difficult to measure

Processes

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

Processes

Estimations and projections on the basis of census data

1. Inter-censal 2. Post-censal3. Future (Projection)

Processes

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