Transcript Getting to the essential

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 wellbeing
• Population movements
• Epidemiology of diseases
Demography
Sources of demographic data
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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
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Each event (birth or death) captured by
two independent procedures
1. Continuous enumeration in population
2. Sample survey every 6 months
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Events matched
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Missing in both systems estimated
Evaluation of SRS
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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
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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
Age pyramid, India, 1961 and 2001
Year 2001
Year 1961
Male
70 +
Female
Male
70 +
Female
65-99
65-69
60-64
60-64
55-59
55-59
50-54
50-54
45-49
45-49
40-44
40-44
35-39
35-39
30-34
30-34
25-29
25-29
20-24
20-24
15-19
15-19
10-14
10-14
5-9
0-4
5-9
0-4
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
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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
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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
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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-censal
3. 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