Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 38


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 37
Using ACS Data 37 competing with the decennial census for Census Bureau resources. The weighted survey response rates for C2SS and the test counties (1999 and 2000 data) were quite high--above 95 percent. Report 6 updates Report 1 by examining the ACS operations for 2001 and 2002. The authors state that their analyses, "provide evidence of improved operational quality from the more than adequate levels achieved during the year 2000."21 During the 2001-2002 period, schedules were maintained and workload levels were close to predicted. The workload issues noted in the first report were resolved because there was no conflict with decennial census activities. Response rates were maintained or improved, and the quality control measures implemented by ACS managers appeared to be effective. 4.2 Data Accumulation over Time and Geography The Census Bureau aggregates ACS data for small geographic units over multiple years before releasing the data to the public. This is done to improve the reliability of the data reported for small geographic levels, where the smaller annual sample sizes are associated with large standard errors. 4.2.1 Census Bureau Multiple-Year Estimation Once the ACS program is fully implemented for Census-defined areas with population under 20,000, five-year moving averages will be released. For census areas with population between 20,000 and 65,000, both three- and five-year moving averages will be released. For areas with population greater than 65,000, annual estimates, three-year moving averages, and five-year moving averages will be released. Table 4.3 shows the percentage of counties and census places in each of the population cate- gories based on Year 2004 Census Bureau population estimates. If five years of fully implemented ACS data were available for 2004 (2000-2004), ACS annual data would be provided for 24 percent Table 4.3. Percentage of counties and census places in ACS population ranges, 2004. Measure United States Counties Census Places Total U.S. Population (2004) 297,550,029 All Counties/Places Number of Areas 3,219 19,465 Population 297,550,029 (100%) 182,048,887 (61%) More than 65,000 Population Number of Areas 780 (24%) 457 (2%) Population 244,171,662 (82%) 95,491,838 (32%) 20,000 to 65,000 Population Number of Areas 1,096 (34%) 1,168 (6%) Population 40,066,827 (13%) 41,336,894 (14%) Less than 20,000 Population Number of Areas 1,343 (42%) 17,840 (92%) Population 13,311,770 (4%) 45,220,155 (15%) Population Outside Areas of this Type 0 115,501,372 (39%) Source: U.S. Census Bureau Population Estimates Program, 2004. 21 U.S. Census Bureau, Meeting 21st Century Demographic Data Needs--Implementing the American Community Sur- vey: Report 6: The 2001-2002 Operational Feasibility Report of the American Community Survey (May 2004), p. iv.

OCR for page 37
38 A Guidebook for Using American Community Survey Data for Transportation Planning of the counties (with those counties comprising 82 percent of the U.S. population). Three-year average data (2002-2004) would be available for 34 percent of the counties (comprising 13 percent of the U.S. population). The remaining 42 percent of counties (4 percent of the population) would have five-year average data reported. For the smaller census geographic areas shown in the table--census places--a much larger percentage (92 percent of census places, with 15 percent of the U.S. population) will have only five-year average data available. An additional 39 percent of the U.S. population does not live in a census-defined place. Figures 4.1 and 4.2 illustrate the availability of single-year ACS estimates for 2004. They show the Minnesota counties and census places for which 2004 ACS data are available. Over time, ACS coverage will improve, but these figures demonstrate that the initial ACS data will have limited scope. Table 4.4 shows the Census Bureau's current estimates of the number of areas for which single and multiyear ACS data will be available for the Census Bureau's main geographic summary levels. The Census Bureau estimates that they will provide single-year ACS estimates for 761 counties. They will produce three-year estimates for those 761 counties, plus another 1,050 coun- ties with populations between 20,000 and 65,000. The remaining 1,330 counties with populations less than 20,000 will have five-year estimates only. When the geographic areas of interest are census tracts, census block groups, or census TAZs, all ACS data will be reported as five-year averages. The combination of data over successive years represents a tradeoff by the Census Bureau, in which the sampling error of the estimates is reduced through the inclusion of greater amounts of data (for multiple years) and data for more current years and with more frequency are made available. This, however, is at the expense of increasing the potential for problems with the inter- Figure 4.1. Minnesota counties with published 2004 ACS data.

OCR for page 37
Using ACS Data 39 Figure 4.2. Minnesota census places with published 2004 ACS data. Table 4.4. ACS reporting for census geographic areas, 2005. Number of Geographic Areas Single Year Three-Year Five-Year Estimates Estimates Estimates Population of Population of Geography 65,000 or More 20,000 or More Nation 1 1 1 Census Regions 4 4 4 Census Divisions 9 9 9 States 51 51 51 Counties 761 1,811 3,141 Minor Civil Divisions 97 592 16,536 Places 476 1,983 25,161 American Indian and Alaska Native Areas 15 41 768 Metropolitan, Micropolitan, and 561 905 923 Consolidated Statistical Areas Congressional Districts 436 436 436 School Districts 879 3,290 14,505 Census Tracts - - 65,443 Block Groups - - 208,790 Source: United States Census Bureau, Design and Methodology: American Community Survey, Technical Paper 67 (May 2006) U.S. Government Printing Office, Washington, D.C.

OCR for page 37
40 A Guidebook for Using American Community Survey Data for Transportation Planning pretation of the estimates that span across the years. For stable, slowly changing small geographic areas and variables that do not vary significantly from year to year, combining multiple succes- sive years of data is not likely to be much of a problem for most analyses. However, for variables that do change significantly and for areas that experience large changes over the years, the inter- pretation of average results will be very difficult. 4.2.2 Multiyear Estimation Procedures22 When multiyear estimates are developed, the most recent year's geography is used. From time to time, census place and county subdivision definitions change to reflect political boundaries and new development. The multiyear estimates treat all records as though they were in the most recent year's geography, whether or not they actually were in previous years. This means where census geographic changes occur, inconsistencies within ACS estimates from year to year and across adjacent geographic areas will be present. All ACS dollar value estimates are inflation adjusted to the most recent year of the three- or five-year period (using yearly midpoint CAPI estimates). Similarly, if census variable categories change, the multiyear data will be presented only for the definitions being used in the most cur- rent year. The Census Bureau develops single-year estimates based on the combination of all 12 months of data collected for that year, without regard to the specific month in which the data are collected. Each year's estimates are controlled to that year's county-level annual population estimates (reflecting population as of July 1 of the year). The one-year ACS estimates and percentages are developed by summing the weighted responses and dividing that sum by the weighted sum of the relevant population. For example, a single-year estimate for the percent of workers who carpool to work would be calculated as follows: Number Who Carpool In Year 1 N Percent Who Carpool In Year 1 = p1 = = 1 Total Number of Workers In Year 1 T1 Census Bureau estimates of medians for a single year are developed by analyzing the weighted data for the full year and identifying the median point of the estimate. Initially, the Census Bureau generated multiyear estimates by computing an average based on each year's individual estimates, so a three-year average estimate for the percent of workers who carpool to work would be computed as the sum of the individual yearly estimates divided by the sum of the individual year totals. However, for full implementation of ACS, the annual samples corresponding to the estimation period will be combined together and the estimates will be developed as they are for the single-year estimates with the control totals being equal to the aver- age of the component year controls. Multiyear median estimates are produced by combining data records from all years, rather than by simply averaging each year's median. An implication of the multiyear calculations is that three- and five-year estimates may not appear completely consistent at first glance with the single-year estimates for the same geography over those three- or five-year periods. Analysts will need to be careful in comparing estimates for areas of different sizes and should carefully consider their analytical needs when deciding which available estimates to use. 22 U.S. Census Bureau, Design and Methodology: American Community Survey, Technical Paper 67 (May 2006) U.S. Government Printing Office, Washington, D.C.

OCR for page 37
Using ACS Data 41 Suppose, for example, an analyst was interested in understanding and reporting on a partic- ular variable in ACS, such as the percentage of workers reporting that they travel more than one hour to their workplaces for a hypothetical geographic area--a county consisting of a moderate- sized city and two small towns. Collectively, the geography has a population of more than 65,000, so annual ACS estimates, three- and five-year estimates will be available for the full geo- graphic area. For the first year of the analysis, 2010, the city population is about 60,000, so three- and five-year ACS estimates will be available, and the two towns both have populations below 20,000, so only five-year estimates are available. Table 4.5 shows hypothetical ACS data and reported estimates for the county and its three county subdivision components for several years. The top portion of the table shows the full set of estimates from a hypothetical ACS. However, not all of these results are made available to data users. The second portion of the table shows the Annual ACS estimates that would be made avail- able for the county. County-level population is available annually for all counties from the Census Bureau Population Estimates Program. In addition, because the county population is more than 65,000, the annual ACS estimates, including those for workers and for workers com- muting more than 60 minutes, are reported for the county. Over time, the population of the city grows to be more than 65,000 as well, so for the last few years shown in the table, annual estimates become available for the city. Unlike the county popu- lation, the city population is derived from the ACS data collection--the county population is used as a control total and the ACS data provide an estimate of the county population living in the city. The annual estimates for the city's workers and workers commuting more than 60 minutes are determined in the same way as the county annual estimates. The third part of the table, shows the hypothetical three-year average data release. Three-year average estimates are available for the county and the city beginning in 2007, and for one of the towns beginning in 2014. The county population estimates are the same as the annual estimates as they are not derived from the ACS and are used as controls, but all the other three-year aver- age estimates are calculated as described above. Because these estimates are three-year averages, the estimates vary both from the published annual estimates and from unpublished actual data. The final part of the table shows the five-year average estimates. Beginning in 2010, the five-year average estimates would be available for the county, the city, and both towns. Like the three-year averages, these estimates are derived by combining data from the five previous years (three previ- ous years for the three-year averages) and controlling the totals to the average of the county's population estimates for the five years. In 2010, the analyst has estimates of workers commuting more than 60 minutes of: 8,789 for the county, based on the countywide annual estimate for 2009; 8,826 for the county, based on the countywide three-year average estimate ending in 2009; 8,749 for the county, based on the countywide five-year average estimate ending in 2009; 5,677 for the city, based on the city three-year average estimate ending in 2009; 5,759 for the city, based on the city five-year average estimate ending in 2009; 1,657 for one of the towns, based on the five-year average estimate ending in 2009; and 1,333 for the other town, based on the five-year average estimate ending in 2009. The choice of how to proceed with these various estimates is the analyst's. If the analyst needs to only look at one geography (say, he or she would like to know the number of long-distance commuters at the county level), then using the annual estimate would seem an attractive choice. At the county level, the annual estimate provides the most timely estimate and relies the least on averaging. Similarly, at the city level, the three-year average would likely be more attractive for

OCR for page 37
Table 4.5. Hypothetical Data Releases for a County and Its City and Towns. Estimates from ACS Collected Data Percent of Workers Commuting Workers Commuting Population Age 16+ Workers More Than 60 Minutes More than 60 Minutes Bee Cee Alpha Bee Cee Alpha Bee Cee Alpha Bee Cee Alpha Year Acity Town Ville County Acity Town Ville County Acity Town Ville County Acity Town Ville County 2005 54,104 12,717 13,025 79,846 22,183 5,214 5,340 32,737 0.24 0.23 0.22 0.24 5,324 1,199 1,175 7,698 2006 55,186 13,607 13,416 82,209 22,074 5,715 5,366 33,155 0.24 0.24 0.22 0.24 5,298 1,372 1,181 7,851 2007 56,290 14,560 13,818 84,668 23,079 6,261 5,665 35,005 0.24 0.25 0.22 0.24 5,539 1,565 1,246 8,350 2008 57,416 15,579 14,233 87,227 22,966 6,699 5,693 35,358 0.24 0.26 0.23 0.24 5,512 1,742 1,309 8,563 2009 58,564 16,669 14,660 89,893 22,840 7,168 5,717 35,725 0.24 0.27 0.24 0.25 5,482 1,935 1,372 8,789 2010 59,735 17,836 15,100 92,671 23,894 7,848 6,040 37,782 0.24 0.28 0.25 0.25 5,735 2,197 1,510 9,442 2011 62,722 19,085 15,553 97,359 25,089 8,206 6,221 39,516 0.24 0.29 0.26 0.25 6,021 2,380 1,617 10,018 2012 65,858 19,466 16,019 101,344 27,002 8,565 6,568 42,135 0.25 0.30 0.27 0.26 6,751 2,570 1,773 11,094 2013 69,151 19,856 16,500 105,506 27,660 8,538 6,600 42,798 0.26 0.31 0.28 0.27 7,192 2,647 1,848 11,687 2014 72,608 20,253 16,995 109,856 29,769 8,709 6,968 45,446 0.27 0.32 0.29 0.28 8,038 2,787 2,021 12,846 ACS Annual Data Release Percent of Workers Commuting Workers Commuting Population Age 16+ Workers More Than 60 Minutes More than 60 Minutes Bee Cee Alpha Bee Cee Alpha Bee Cee Alpha Bee Cee Alpha Year Acity Town Ville County Acity Town Ville County Acity Town Ville County Acity Town Ville County 2005 n n n 79,846 n n n 32,737 n n n 0.24 n n n 7,698 2006 n n n 82,209 n n n 33,155 n n n 0.24 n n n 7,851 2007 n n n 84,668 n n n 35,005 n n n 0.24 n n n 8,350 2008 n n n 87,227 n n n 35,358 n n n 0.24 n n n 8,563 2009 n n n 89,893 n n n 35,725 n n n 0.25 n n n 8,789 2010 n n n 92,671 n n n 37,782 n n n 0.25 n n n 9,442 2011 n n n 97,359 n n n 39,516 n n n 0.25 n n n 10,018 2012 65,858 n n 101,344 27,002 n n 42,135 0.25 n n 0.26 6,751 n n 11,094 2013 69,151 n n 105,506 27,660 n n 42,798 0.26 n n 0.27 7,192 n n 11,687 2014 72,608 n n 109,856 29,769 n n 45,446 0.27 n n 0.28 8,038 n n 12,846

OCR for page 37
Table 4.5. (Continued). ACS Three-Year Average Data Release Percent of Workers Commuting Workers Commuting Population Age 16+ Workers More Than 60 Minutes More than 60 Minutes Bee Cee Alpha Bee Cee Alpha Bee Cee Alpha Bee Cee Alpha Year Acity Town Ville County Acity Town Ville County Acity Town Ville County Acity Town Ville County 2005 -- -- -- 79,846 - - - - -- -- -- -- - - - - 2006 -- -- -- 82,209 - - - - -- -- -- -- - - - - 2007 56,822 n n 84,668 23,108 n n 34,625 0.24 n n 0.24 5,546 n n 8,201 2008 57,976 n n 87,227 23,383 n n 35,535 0.24 n n 0.24 5,612 n n 8,501 2009 59,154 n n 89,893 23,654 n n 36,429 0.24 n n 0.24 5,677 n n 8,826 2010 60,356 n n 92,671 23,941 n n 37,394 0.24 n n 0.25 5,746 n n 9,203 2011 62,960 n n 97,359 24,980 n n 39,310 0.24 n n 0.25 5,995 n n 9,825 2012 65,498 n n 101,344 26,428 n n 41,540 0.24 n n 0.26 6,437 n n 10,627 2013 68,577 n n 105,506 27,659 n n 43,162 0.25 n n 0.26 6,924 n n 11,376 2014 72,016 20,665 n 109,856 29,286 8,953 n 45,225 0.26 0.31 n 0.27 7,624 2,776 n 12,358 ACS Five-Year Average Data Release Percent of Workers Commuting Workers Commuting Population Age 16+ Workers More Than 60 Minutes More than 60 Minutes Bee Cee Alpha Bee Cee Alpha Bee Cee Alpha Bee Cee Alpha Year Acity Town Ville County Acity Town Ville County Acity Town Ville County Acity Town Ville County 2005 -- -- -- 79,846 - - - - -- -- -- -- - - - - 2006 -- -- -- 82,209 - - - - -- -- -- -- - - - - 2007 -- -- -- 84,668 - - - - -- -- -- -- - - - - 2008 -- -- -- 87,227 - - - - -- -- -- -- - - - - 2009 59,716 15,511 14,666 89,893 23,996 6,587 5,892 36,475 0.24 0.25 0.23 0.24 5,759 1,657 1,333 8,749 2010 60,948 16,607 15,116 92,671 24,374 7,150 6,044 37,569 0.24 0.26 0.23 0.24 5,850 1,870 1,404 9,125 2011 63,509 18,042 15,808 97,359 25,399 7,797 6,321 39,517 0.24 0.27 0.24 0.25 6,096 2,116 1,520 9,732 2012 65,824 19,173 16,346 101,344 26,345 8,325 6,541 41,212 0.24 0.28 0.25 0.25 6,381 2,341 1,640 10,363 2013 68,498 20,139 16,870 105,506 27,415 8,741 6,751 42,906 0.25 0.29 0.26 0.26 6,758 2,542 1,760 11,061 2014 71,557 20,920 17,379 109,856 28,923 9,076 7,023 45,023 0.25 0.30 0.27 0.27 7,314 2,727 1,901 11,942