🪵Intro to Demographic Methods Unit 2 – Data Sources: Census, Vital Stats, Surveys

Key Concepts and Definitions

• Demography studies the characteristics, dynamics, and structure of human populations
• Population composition refers to the distribution of various attributes within a population (age, sex, race, marital status)
• Population dynamics encompass the processes that change population size and composition over time (fertility, mortality, migration)
• Cohort is a group of individuals who experience the same event within the same time period (birth cohort, marriage cohort)
• Period refers to a specific point in time or a defined time interval for which data is collected and analyzed
• Rates measure the frequency of demographic events relative to the population at risk (crude birth rate, age-specific mortality rate)
  • Calculated as the number of events divided by the population at risk, often expressed per 1,000 or 100,000 people
• Population pyramid graphically represents the age-sex structure of a population

Types of Demographic Data Sources

• Census data provides comprehensive information on population size, composition, and distribution at a specific point in time
• Vital statistics record vital events such as births, deaths, marriages, and divorces
• Sample surveys collect detailed information from a representative subset of the population
• Administrative records include data collected by government agencies for various purposes (tax records, social security data)
• Population registers continuously update individual-level information on vital events and migration
• Ethnographic data provides qualitative insights into population dynamics and cultural contexts
• Big data sources (social media, mobile phone records) offer new opportunities for demographic analysis

Census: Purpose and Methodology

• A census aims to enumerate and collect information on an entire population at a specific point in time
• Provides a snapshot of population size, composition, and distribution
• Typically conducted every 5 or 10 years, depending on the country
• Census questionnaires collect data on demographic, social, and economic characteristics
  • Core questions cover age, sex, marital status, household composition, and housing characteristics
  • Additional topics may include education, employment, income, and migration history
• Census data is collected through self-enumeration (households complete questionnaires) or interviews by trained enumerators
• Data processing involves coding, editing, and imputation to ensure data quality and consistency
• Census results are disseminated through published reports, online databases, and microdata files

Vital Statistics: Recording Life Events

• Vital statistics systems continuously record the occurrence and characteristics of vital events
• Vital events include births, deaths, marriages, divorces, and fetal deaths
• Legal requirements mandate the registration of vital events with civil registration authorities
• Birth records provide information on the newborn (sex, weight, gestational age) and parents (age, education, occupation)
• Death records include data on the deceased (age, sex, cause of death) and circumstances of death
• Marriage and divorce records capture the formation and dissolution of legal unions
• Vital statistics data is compiled and published by national statistical offices or health ministries
• Provides timely information on fertility, mortality, and nuptiality patterns
• Allows for the calculation of key demographic indicators (crude birth rate, infant mortality rate, total fertility rate)

Surveys: Sampling and Implementation

• Sample surveys collect detailed information from a representative subset of the population
• Probability sampling ensures that each unit in the population has a known, non-zero chance of being selected
  • Simple random sampling selects units randomly from the entire population
  • Stratified sampling divides the population into homogeneous subgroups (strata) and samples independently within each stratum
  • Cluster sampling involves selecting clusters (geographic areas, institutions) and then sampling units within selected clusters
• Survey questionnaires are designed to capture information relevant to the research objectives
• Interviewer-administered surveys (face-to-face, telephone) allow for clarification and probing
• Self-administered surveys (mail, online) provide respondents with more privacy and flexibility
• Surveys can be cross-sectional (data collected at one point in time) or longitudinal (repeated measurements over time)
• Specialized demographic surveys focus on specific topics (fertility, migration, health) or subpopulations (youth, elderly)

Data Collection Techniques

• Face-to-face interviews involve direct interaction between the interviewer and respondent
  • Allows for clarification, probing, and observation of non-verbal cues
  • Suitable for complex questionnaires and low literacy populations
• Telephone interviews are conducted remotely using landline or mobile phones
  • Cost-effective and efficient for reaching dispersed populations
  • Limited to short questionnaires and populations with high telephone coverage
• Self-administered questionnaires are completed by respondents without an interviewer's assistance
  • Mail surveys send questionnaires to sampled households and rely on postal return
  • Online surveys use web-based platforms to collect data from internet users
  • Provides greater anonymity and reduces interviewer bias
• Computer-Assisted Personal Interviewing (CAPI) uses electronic devices to administer surveys in-person
  • Allows for real-time data validation, complex skip patterns, and multimedia content
• Computer-Assisted Telephone Interviewing (CATI) automates telephone survey administration
• Mixed-mode surveys combine multiple data collection methods to improve response rates and representativeness

Strengths and Limitations of Each Source

• Census data provides comprehensive coverage and detailed geographic granularity
  • Allows for analysis of small population subgroups and local-level planning
  • Limited by the decennial frequency and the risk of undercounting hard-to-reach populations
• Vital statistics offer continuous and timely data on fertility, mortality, and nuptiality
  • Captures rare events (maternal deaths) and provides cause-of-death information
  • Data quality depends on the completeness and accuracy of event registration
• Sample surveys enable the collection of detailed and specialized information
  • Provides flexibility in questionnaire design and allows for in-depth exploration of topics
  • Subject to sampling and non-sampling errors, and limited generalizability to the entire population
• Administrative records leverage existing data collected for non-statistical purposes
  • Cost-effective and can provide longitudinal information on individuals
  • Data quality and completeness may vary across sources and over time
• Big data sources offer high volume, velocity, and variety of data
  • Enables real-time monitoring and analysis of population dynamics
  • Biases in digital access and usage limit representativeness and interpretability

Real-World Applications and Case Studies

• Census data informs electoral redistricting, infrastructure planning, and resource allocation
  • The US Census Bureau's decennial census guides the apportionment of congressional seats and the distribution of federal funds
• Vital statistics are used to monitor public health, evaluate interventions, and inform policy
  • The Maternal Mortality Surveillance System in the US relies on death certificates and linkage with other data sources to identify and investigate maternal deaths
• Fertility surveys, such as the Demographic and Health Surveys (DHS), provide insights into reproductive health and family planning
  • DHS data has been used to assess the impact of contraceptive prevalence on fertility rates in sub-Saharan Africa
• Labor force surveys, like the Current Population Survey (CPS) in the US, monitor employment, unemployment, and labor market dynamics
  • CPS data is used to calculate the official unemployment rate and track disparities by age, sex, and race/ethnicity
• The WorldPop project combines census, survey, and geospatial data to produce high-resolution population distribution maps
  • These maps support disaster response, disease surveillance, and resource targeting in low- and middle-income countries
• Mobile phone call detail records have been used to estimate population displacement and migration flows
  • Analysis of mobile phone data provided insights into the spatial distribution of population movements following the 2010 Haiti earthquake