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Population Estimates and Projections ASDC Annual Meeting Carolyn Trent, Socioeconomic Analyst Center for Business and Economic Research November 10, 2011 Culverhouse College of Commerce and Business Administration The University of Alabama
Measuring the population • Census of Population: Actual enumeration of the population of an area on a given date. • Population Estimate: Calculated population of an area on a date which has already passed. • Population Projection: Calculation of what the population of an area may be at a specified future date(s). Note: An estimate or projection is generally more reliable the larger the population being determined and the less detail required.
Census of Population • Census 2010 counted population, collecting • Age, sex, race, ethnicity • Household size and composition, type of unit, ownership • Separately enumerated group quarters • Sources of error: • Some people likely not counted (mail participation rates: Alabama 72%, United States 74%; others counted in follow-up activities) • People may not accurately report their age, race, ethnicity • All other socioeconomic data now from ACS
Alabama Population, 1950-2010 2000-2010 Gain: Alabama 7.5% U.S. 9.7% Change from Census Previous Census April 1 Number Percent 1950 3,061,743 1960 3,266,740 204,997 6.7 1970 3,444,165 177,425 5.4 1980 3,893,888 449,723 13.1 4,040,587 146,699 3.8 2000 4,447,100 406,513 10.1 2010 4,779,736 332,636 7.5 Source: U.S. Census Bureau. Center for Business and Economic Research, The University of Alabama
Population Estimates • Alabama uses the Census Bureau’s annual population estimates. CBER supplies data for these estimates through the FSCPE. • Census estimates: • Calculated as of July 1 each year • Produced at the state, county, subcountylevels • Used as controls for ACS data • County series uses administrative records data; state is calculated as sum of counties • Subcounty estimates (places, balance of county) look at housing unit change • Entire series is recalculated each year • Reviewed by CBER/ASDC before finalized and released
Census Bureau Population Estimates Schedule Note: All releases below are July 1, 2011 estimates. • U.S. and state population and components of change 12/11 • County population and components of change 04/12 • Metropolitan and micro area population 04/12 • State population by age/sex 05/12 • State/county population by age/sex/race/Hispanic origin 05/12 • Place/county subdivision population 06/12 • State and county housing unit estimates 06/12
State/County Estimates • Based on administrative records • Births and deaths annually from FSCPE and NCHS • Net domestic migration under 65 population from federal income tax returns, military movements • Net domestic migration 65+ from Medicare enrollees • Net international migration from ACS, Census, other sources • Group Quarters • Begin with Census count of GQs by county • Census data by type of GQ, but we don’t have a list of GQs that were counted • Annual updates of GQ populations sent in by CBER (FSCPE). Also report new GQs.
Subcounty/Housing Unit Estimates • Housing units estimated annually for every county and subcounty geography • Begin with Census 2010 base • Add estimate of new construction in prior year, using Census Bureau building permit data. Assume 6-month lag from permit date to completion. • For areas without permits, estimate non-permitted construction from annual Survey of Construction (SOC) • Add new mobile home placements • Subtract estimate of housing loss using percentages derived from 1999-2007 American Housing Survey (AHS) • Use these housing unit estimates to distribute county estimate totals to subcounty geographies • Used as controls for ACS housing units
PostcensalvsIntercensalEstimates • Postcensal estimates—fordecade following a census • Build on Census 2010 count, modified by differences from boundary changes to create estimates base • New vintage every year replaces prior years • Intercensal estimates—estimatesfor2000 to 2009 were recalculated to end up at the Census 2010 count. • Alabama’s July 1, 2009 postcensal estimate was too low: • Postcensal 4,708,708 Intercensal 4,757,938 • Difference of 49,230 (1.0 percent)
Challenges to Estimates Localities are given the opportunity to challenge their population estimates. • Challenges usually based on housing unit counts • Challenge process suspended early in 2010; will resume when the July 1, 2011 estimates are released • Census Bureau is reevaluating the challenge process and will issue new guidelines • In the past, most challenges were approved, but not likely to be the case in the future • For places that had challenges accepted during the past decade, Census Bureau analysis showed that the 2010 original population estimate tended to be closer to the 2010 Census result than the estimate with the challenge • During the past decade, 6 Alabama cities and towns won challenges, for a combined total of 3,913 residents added
How do disruptions affect estimates? • April 27 tornadoes • Tax returns were sent in by April 18, 2011. So IRS address changes resulting from the destruction won’t show up until 2012—when people may have already moved back or again. The July 1, 2011 population estimate likely won’t be correct for hard hit areas. • Additional data was collected to calculate population estimates after Hurricane Katrina for impacted areas. • New immigration law • Push to count Hispanics in Census 2010—legal or illegal • From that base count, how do we assess outmigration in response to the law? • Also problem for population projections
Population Projections • Prepared by the Center for Business and Economic Research for over 40 years. • Utilize a cohort component model of the form: Pop(new) = pop(old) + births – deaths + in-migration – out-migration • Calculated for the state and counties for 5-year age groups from 0-4 to 80-84 and 85+, for males/females, races white/black and other. • Currently working on new projections based on Census 2010—will be available in the Spring.
Projections data inputs • For the state and each county, the following are compiled: • Population by age/race/sex for 2000 and 2010 • Total number of births by race of mother and sex of child for 2000 through 2010 (from Alabama Center for Health Statistics) • Total number of deaths by race, sex, and age group for 2000 through 2010 (from ACHS) • Census 2010 group quarters population
Projections data calculations • From the data above, CBER calculates for the state and counties: • Total fertility rate by race for women aged 15 to 44 in 2010 • Percent of all births for 2000 to 2010 that were male and female • Death rates by age group/race/sex for 2010 • Percentage of total 2010 population in group quarters. For counties with large GQ populations, an estimate of that population by age group/race/sex will be subtracted before running the projections and then added back in.
Further data modifications • The dataset created for each geography is examined to see if rates are reasonable and modified as needed: • If large college/university population, birth rate may be dampened as college students are less likely to have children • For small counties, there may not be enough individuals in a particular age/race/sex group and death rates for that group may be substituted from a larger group • Using national life tables, death rates for every geography are modified in each five-year interval to reflect changes in expected mortality and life span.
Producing Projections • The cohort-component program is run separately for the state and each county. • The cohort aspect of the projection process is that the population in each 5-year age group is aged over the 10-year intercensal period—i.e., individuals who were 20-24 in 2000 will be 30-34 in 2010. • The unknown part of the projection is migration rates, which are derived as the residual of the change from 2000 to 2010 after adding births to the 2000 base population and subtracting deaths. • Migration rates are dampened for each 5-year projection period under the assumption that the rate of people leaving a county will slow over time as will the rate of individuals moving in. • County results were adjusted to sum to the state total, although we may change to summing counties to create state total.
How did CBER do last decade? • Sources of error for projections: • Trends may change in ways that weren’t expected • Changes in institutional populations can’t be predicted • Economic development and economy in general affect migration • In projections for 2010 done right after the 2000 Census, CBER was a little too high for Alabama: • Census 2010 4,779,736 • CBER 2010 projection 4,838,812 Difference 59,073 (1.2 percent) • Projections are rerun periodically during the decade, taking into account more recent estimates totals • Most recent series controls state and county 2010 totals to Census 2010, but is driven by 1990 to 2000 trends
Small area population projections • CBER can calculate population projections for areas down to the block group level. These are done on a contract basis. • Change between the two most recent censuses is used as a starting point. • A variety of other information, including building permits, infrastructure development, and recent or upcoming economic development are collected for the geographies to be projected. • ACS data, such as age of housing stock and income levels, is also used. Land area and housing density are examined. • CBER small area projections have been used for regional transportation plans and in socioeconomic impact studies for highway projects.
Check CBER website for data • Projections are posted to CBER website http://cber.cba.ua.edu under Data, Maps, and Presentations • When new series of projections is complete, summary Excel files will be available there • Detailed age/race/sex projections will not be posted due to their size, but will be available on CD from CBER for purchase • Look for these in March 2012 Thank you!