# Population Estimates and Projections in the U. S. John F. Long www.usademography.com.

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Population Estimates and Projections in the U. S. John F. Long www.usademography.com

Population Estimates and Projections  Both Estimates and Projections –Calculate the size of the population in the absence of complete demographic data –May also calculate demographic characteristics –Are used for planning and policy decisions  Population Projections –Project trends beyond the time interval of the input data –Use mathematical models of varying sophistication –Often use models of components of demographic change: births, deaths, migration, and immigration  Population Estimates –Estimate population using data from the same time period –May use demographic data: births and deaths –May use indicator variables – housing, administrative records

Projection: Simple Extrapolation P x+1 t+1 = (P x t ) ((P x t )/(P x-1 t-1 )) where, P x t is the population age x in a given place at time t

U.S. Population: Census Counts from 1790 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 Using Components of Change  Begins with a measured base population (census, etc)  Calculates trends in births, death, migration  Usually based on cohort-component method  May used multi-regional projection matrix methods  Accepted method for official U.S. population projections

Population A by age, race, and sex Place A Population B by age, race, and sex Place B Population C by age, race, and sex Place C Migration

Component-based Projections P x+1 t+1 = P x t + B (if x<0) - D x + I x - O x where, P x 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+1 D x is then number of deaths age x in a given place between t and t+1 I x is the number of in-migrants age x to a given place between t and t+1 O x is the number of out-migrants age x from a given place between t and t+1.

Development of Demographic Accounting Approach –Nationwide birth and death registration began in the early 1900’s –Estimates and projections for states, counties, and places developed in the last half of the 20 th century –Demographic Analysis became a key tool to evaluate decennial census quality –“Integrated” accounting system implicit in the American Community Survey for the 21 st century

Elements of US Demographic Accounting System  Master Address Files  Decennial Censuses  Birth and Death Registers (NCHS)  Immigration Data (INS & ACS)  Domestic Migration Data (IRS)  Adjustments and Corrections  American Community Survey

Master Address Files  Importance of tying population to geography  Address canvassing prior to census year  Corrections during census operation  Updates between censuses  Provides “frame” for census and survey operations  Issues with permits, construction, demolitions, and conversions  Addresses vs. physical location.

Decennial Census Counts  Base on which all of system is built  Provides ground truth check of accounting system  Key demographic data collected: location, relationship, sex, age, race, Hispanic origin

Measure Death and Birth Components  Birth Registration – Ties birth to place of residence of mother –Race data is for parents not child – and uses older classification system –Completeness of registration is assumed  Death registration –Ties death to place of residence or last address? –Race is not self reported –Completeness and speed of tabulation is an issue

Estimating International Migration Flows  Legal immigration –Difference between residence change and legal status change –Problems with place of intended residence –Completeness issues  Legal Emigration –Lack of data collection when leaving the country –Problems of using other countries data  Illegal immigration –Methods are often indirect –Question of census coverage  Alternative data from the American Community Survey

Measuring Domestic Migration  Use of matched IRS returns to provide county in and out migration  Coverage of IRS data  Assigning age, race, hispanic origin, and sex data  Timing of data collection and tabulation

Develop Yearly Population Estimates and Controls  Develop annual national, state, county, and place data for funding and other administrative uses  Provide county age, race, sex, Hispanic origin controls for the American Community Survey  Issues of timeliness and accuracy of input data

Problems with an Accounting System  Errors in specifying the system can multiply over time  Errors in data input can cause faulty results  Structure of the system may change over time

Reconcile with new decennial census data  Need to recalibrate estimates from demographic accounting with decennial census results  Census coverage error vs. population estimation error  Incorporating “error of closure” corrections into new estimates.

Reconciling Inventory and Accounting Systems  Audit of the current demographic accounts –Differences with a Population Register –Potential inconsistencies in the system –Future Hazards and Opportunities