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  Pilot basis  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 procedures 1.Continuous enumeration in population 2.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

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-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