Overview of Demographic Data

Transcription

1 Overview of Demographic Data Michael Ratcliffe Geography Division US Census Bureau Mapping Sciences Committee October 20, 2014

2 Sources of Demographic Data Censuses Full enumeration, or counting, of the population. Additional population and housing characteristics generally are collected at the time of enumeration. Population Registers/Vital Registries Birth certificates Death certificates Surveys Data collected from a sample of the population or households 2

3 Sources of Demographic Data Estimates and Projections An estimate is the calculated number of people living in an area as of a specified time, usually July 1. Calculated for years preceding the date of release; e.g., July 1, 2013 estimates released in A projection is an estimation of population at some future date. Administrative Records Data collected as part of various programs or processes, but can be used to provide information about populations, demographic characteristics, or population processes. Example: Because IRS tax returns contain the county in which the filer lives, data about migration can be derived from two successive years of tax returns. 3

4 Data Tabulation Programs Decennial Census of Population and Housing: every 10 years Population Estimates and Projections Program: every year Small Area Income and Poverty Estimates Program: every year American Community Survey: every year Economic Census: every 5 years Local Employment Dynamics Program: every year Census of Governments: every 5 years Over 100 Annual, Quarterly or Monthly Surveys, including 13 principal economic indicators

5 Geography and Data Availability Availability of data by geographic entity varies across and within data tabulation programs due to: Data reliability concerns Ability to geocode responses Data disclosure concerns Sources of input data Cost of collection, processing, and tabulation 5

6 Population Registers/Vital Registries Comprehensive data source, assuming everyone registers Have replaced censuses in some countries Data collected and updated continuously, either directly or indirectly Requires that people register changes in life events (births, deaths, moves), or that government agencies update records 6

7 Population Estimates and Projections Population Projections Cohort-component method: components of change estimated for each birth cohort Based on most recent census United States (low, middle, and high series) State (historical, based on 2000 Census) Population Estimates US, state, and county estimates based on demographic components of change Place and county subdivision estimates based on the housing unit method Based on most recent census 7

8 Population Estimates May use a demographic components method: PopYear 2 = Base pop + (Births Deaths) + (In migration Out migration) Vital registers (birth registers and death registers) will form the basis for the first portion of the equation; administrative records for multiple years can provide migration data May use a housing unit method PopYear 2 = (Base # of housing units + (New units demolished units)) x average # of persons per housing unit Simple Interpolation method: assume that the amount or rate of change observed over one time period will be a good indicator of change for another. Problem: population change is not smooth over time 8

9 Estimates and Projections Generally use census data as a source for base counts Generally use administrative data as inputs Sources of error: Missing information in input files Insufficient input files This is a particular problem with regard to estimating illegal immigration IRS tax returns provide good sources for county-to-county migration, but not everyone files a tax return Incorrect assumptions about numbers of people per housing unit Not taking into account geographic changes that alter the base count or the characteristics of the base population 9

10 Sample Surveys Accuracy and reliability depend on size of sample and the degree to which each respondent (individual or household) is representative of other households. Generally collected at place of residence Generally collect data as of a specific reference date Point estimates: all data referenced to a single date. For example, Census Day. Period estimates: data collected over a period of time. The American Community Survey collects data from a sample of households every month, then averages the data over a year. Sources of error Non-sampling error (respondent error; data captured incorrectly) Sampling error (households or individuals in sample not representative of other households) 10

11 American Community Survey Source of detailed demographic and housing characteristics, including: Income Language spoken at home Educational attainment Occupation Place of work and journey to work Data collected annually from approximately 3 million households per year. Approximately 250,000 households per month. Data collected throughout the year produces period estimates rather than point estimates. ACS 1-Year Data ACS 3-Year Data ACS 5-Year Data Geographic Areas 65,000 or more population 20,000 or more population All areas, block group or higher 11

12 2011 Language Mapper 12

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14 Current Population Survey Monthly survey of about 50,000 households Primary source of labor force characteristics Monthly supplements collecting other characteristics Small sample size means data reliable only for Nation and some states Source of data for models for state- and countylevel data 14

15 Differences between data sets: What is the population? Place 2010 Census ACS ACS Population Estimates Program July 1, 2010 July 1, 2012 Total Pop Estimate MOE Estimate MOE 2010 Base Estimate Estimate Baltimore city 620, ,843 (---) 620,644 (---) 621, , ,417 Columbia CDP 99, ,512 2, ,735 1,435 N/A N/A N/A Laurel city 25,115 25, , ,115 25,192 25,565 North Laurel CDP 4,474 N/A 19,810 1,022 N/A N/A N/A Why does Baltimore s 2010 base count differ from the 2010 Census total population? Possible answer: geocoding enhancements and/or corrections relative to boundary. What happened with North Laurel? Boundary error in 2010 tabulation; corrected after data were tabulated and released. 15

16 Income and Poverty Data Sources Census Bureau: American Community Survey Current Population Survey Survey of Income and Program Participation Small Area Income and Poverty Statistics Bureau of Economic Analysis Annual and Quarterly State Personal Income Metro Area and Local Area (county) Personal Income and Wages Bureau of Labor Statistics National Compensation Survey Occupational Employment Statistics Survey 16

17 Measuring Poverty 17

18 Measuring Poverty 18

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20 Gridded Population Maps from Census Bureau: Demobase

21 Examples of construction of gridded data Alex de Sherbinin, NASA Socioeconomic Data and Applications Center, CIESIN The Earth Institute at Columbia University, USA

22 Data for Places and County Subdivisions Decennial Census American Community Survey Population Estimates Program Economic Census Incorporated Places All All, in 5-year estimates All 2,500 or more persons/jobs Census Designated Places All All, in 5-year estimates MCDs All All, in 5-year estimates Not included 2,500 or more persons/jobs. No CDP data in 12 strong MCD states 20 states only 12 states only CCDs All All, in 5-year estimates Not included Not included 22

23 Census ACS Population Estimates Population Projections CPS LED Economic Census Regions Divisions All All All All All All All States All All All All All All All Counties All All All None None All All County Subdivs. All All MCDs in 20 states None None All MCDs in 12 states Places All All Inc. places only None None All 2,500 persons or 2,500 jobs Tracts and BGs All All None None None All None Blocks All None None None None All None 23

24 Hierarchy of Census Geographic Entities 24

25 Relationship between county subdivisions and census tracts in counties of small population size The typical assumption is that geographic entities located higher on the Census Bureau s geographic hierarchy are larger in population and areal extent than entities lower on the hierarchy. This also implies that entities at the lower end of the hierarchy provide greater spatial resolution. Minimum population thresholds for some statistical geographic entities, however, mean that this is not always true, particularly in counties of smaller population sizes. Ratcliffe County has a census population of 8,000, divided between two census tracts (9400 and 9401). The minimum population for a census tract is 1,200; the maximum is 8,000; optimum population is 4,000. Therefore, Ratcliffe County can be divided into two census tracts, each with a population at or close to the optimum population. 25

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30 Census Tract Thematic Map Viewer 30

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32 Questions? Michael Ratcliffe Geography Division