Population Estimates and Population Estimates and Projections in the U. S.Projections in the U. S.

John F. LongJohn F. Long

www.usademography.comwww.usademography.com

Population Estimates and Population Estimates and ProjectionsProjections

Both Estimates and Projections Both Estimates and Projections – Calculate the size of the population in the absence of complete demographic Calculate the size of the population in the absence of complete demographic

datadata– May also calculate demographic characteristicsMay also calculate demographic characteristics– Are used for planning and policy decisionsAre used for planning and policy decisions

Population ProjectionsPopulation Projections– Project trends beyond the time interval of the input dataProject trends beyond the time interval of the input data– Use mathematical models of varying sophisticationUse mathematical models of varying sophistication– Often use models of components of demographic change: births, deaths, Often use models of components of demographic change: births, deaths,

migration, and immigrationmigration, and immigration

Population EstimatesPopulation Estimates– Estimate population using data from the same time periodEstimate population using data from the same time period– May use demographic data: births and deathsMay use demographic data: births and deaths– May use indicator variables – housing, administrative recordsMay use indicator variables – housing, administrative records

Projection: Simple ExtrapolationProjection: Simple Extrapolation

PPx+1x+1

t+1t+1 = (P = (Pxx

tt ) ((P ) ((Pxx

tt )/(P )/(Px-1x-1

t-1t-1))))

where, where,

PPxx

tt is the population age x in a given place at is the population age x in a given place at

time time tt

U.S. Population: Census Counts from U.S. Population: Census Counts from 1790 and Projections for 1860-19301790 and Projections for 1860-1930

Source: U.S Census Bureau, Decennial Censuses 1790-1930 ; Abraham Lincoln, “Annual Message to Congress: December 1, 1862”.

Population Projections UsingPopulation Projections UsingComponents of ChangeComponents of Change

Begins with a measured base population (census, etc)Begins with a measured base population (census, etc) Calculates trends in births, death, migrationCalculates trends in births, death, migration Usually based on cohort-component method Usually based on cohort-component method May used multi-regional projection matrix methodsMay used multi-regional projection matrix methods Accepted method for official U.S. population projectionsAccepted method for official U.S. population projections

Migration

Migration

Component-based ProjectionsComponent-based Projections

PPx+1x+1

t+1t+1 = P = Pxx

tt + B (if x<0) - D + B (if x<0) - Dxx + I + I

xx - O - O

xx

where, where,

PPxx

tt is the population age x in a given place at time t is the population age x in a given place at time t

B is the number of births in a given place between t and t+1B is the number of births in a given place between t and t+1

DDxx is then number of deaths age x in a given place between t and t+1 is then number of deaths age x in a given place between t and t+1

IIxx is the number of in-migrants age x to a given place between t and t+1 is the number of in-migrants age x to a given place between t and t+1

OOxx is the number of out-migrants age x from a given place between t is the number of out-migrants age x from a given place between t

and t+1.and t+1.

Development of Demographic Development of Demographic Accounting ApproachAccounting Approach

– Nationwide birth and death registration began in the early 1900’sNationwide birth and death registration began in the early 1900’s– Estimates and projections for states, counties, and places Estimates and projections for states, counties, and places

developed in the last half of the 20developed in the last half of the 20thth century century– Demographic Analysis became a key tool to evaluate decennial Demographic Analysis became a key tool to evaluate decennial

census qualitycensus quality– ““Integrated” accounting system implicit in the American Community Integrated” accounting system implicit in the American Community

Survey for the 21Survey for the 21stst century century

Elements of US Demographic Elements of US Demographic Accounting SystemAccounting System

Master Address FilesMaster Address Files Decennial CensusesDecennial Censuses Birth and Death Registers (NCHS)Birth and Death Registers (NCHS) Immigration Data (INS & ACS)Immigration Data (INS & ACS) Domestic Migration Data (IRS)Domestic Migration Data (IRS) Adjustments and CorrectionsAdjustments and Corrections American Community SurveyAmerican Community Survey

Master Address FilesMaster Address Files

Importance of tying population to geographyImportance of tying population to geography Address canvassing prior to census yearAddress canvassing prior to census year Corrections during census operationCorrections during census operation Updates between censusesUpdates between censuses Provides “frame” for census and survey operationsProvides “frame” for census and survey operations Issues with permits, construction, demolitions, and Issues with permits, construction, demolitions, and

conversionsconversions Addresses vs. physical location.Addresses vs. physical location.

Decennial Census CountsDecennial Census Counts

Base on which all of system is builtBase on which all of system is built Provides ground truth check of accounting systemProvides ground truth check of accounting system Key demographic data collected: location, relationship, sex, Key demographic data collected: location, relationship, sex,

age, race, Hispanic originage, race, Hispanic origin

Measure Death and Birth Measure Death and Birth ComponentsComponents

Birth RegistrationBirth Registration– Ties birth to place of residence of motherTies birth to place of residence of mother– Race data is for parents not child – and uses older classification Race data is for parents not child – and uses older classification

systemsystem– Completeness of registration is assumedCompleteness of registration is assumed

Death registrationDeath registration– Ties death to place of residence or last address?Ties death to place of residence or last address?– Race is not self reportedRace is not self reported– Completeness and speed of tabulation is an issueCompleteness and speed of tabulation is an issue

Estimating International Migration Estimating International Migration FlowsFlows

Legal immigrationLegal immigration– Difference between residence change and legal status changeDifference between residence change and legal status change– Problems with place of intended residenceProblems with place of intended residence– Completeness issuesCompleteness issues

Legal EmigrationLegal Emigration– Lack of data collection when leaving the countryLack of data collection when leaving the country– Problems of using other countries dataProblems of using other countries data

Illegal immigrationIllegal immigration– Methods are often indirectMethods are often indirect– Question of census coverage Question of census coverage

Alternative data from the American Community SurveyAlternative data from the American Community Survey

Measuring Domestic MigrationMeasuring Domestic Migration

Use of matched IRS returns to provide county in and out Use of matched IRS returns to provide county in and out migrationmigration

Coverage of IRS dataCoverage of IRS data Assigning age, race, hispanic origin, and sex dataAssigning age, race, hispanic origin, and sex data Timing of data collection and tabulationTiming of data collection and tabulation

Develop Yearly Population Develop Yearly Population Estimates and ControlsEstimates and Controls

Develop annual national, state, county, and place data for Develop annual national, state, county, and place data for funding and other administrative usesfunding and other administrative uses

Provide county age, race, sex, Hispanic origin controls for Provide county age, race, sex, Hispanic origin controls for the American Community Surveythe American Community Survey

Issues of timeliness and accuracy of input dataIssues of timeliness and accuracy of input data

Problems with an Accounting Problems with an Accounting SystemSystem

Errors in specifying the system can multiply over Errors in specifying the system can multiply over timetime

Errors in data input can cause faulty resultsErrors in data input can cause faulty results Structure of the system may change over timeStructure of the system may change over time

Reconcile with new decennial Reconcile with new decennial census datacensus data

Need to recalibrate estimates from demographic accounting with Need to recalibrate estimates from demographic accounting with decennial census resultsdecennial census results

Census coverage error vs. population estimation errorCensus coverage error vs. population estimation error

Incorporating “error of closure” corrections into new estimates.Incorporating “error of closure” corrections into new estimates.

Reconciling Inventory and Reconciling Inventory and Accounting SystemsAccounting Systems

Audit of the current demographic accountsAudit of the current demographic accounts

– Differences with a Population RegisterDifferences with a Population Register– Potential inconsistencies in the systemPotential inconsistencies in the system– Future Hazards and OpportunitiesFuture Hazards and Opportunities