The entire population continually ages into older age groups over time and babies fill in the youngest age group. So, the population of a certain age is made up of a completely different group of people from one time period to the next. Since populations occasionally experience booms/increases and busts/decreases in births, deaths, or migration (for example, the postwar Baby Boom from 1946-1964), one should not necessarily expect that the population in an age group in Census 2000 should be similar in size or proportion to the population in the same age group in different data year(s). For example, Baby Boomers were age 36 to 54 in Census 2000 while they were age 46 to 64 in the 2010 ACS 1-year, between ages 44 to 64 in the 2008-2010 3-year period, and between ages 42 to 64 in the 2006-2010 5-year period. So, the age group 55 to 59 would show a considerable increase in population when comparing Census 2000 data with the single year or multiyear ACS data. 

Data from the 2010 ACS were controlled to independent estimates of the population by sex, age, race, and Hispanic origin that were based on the 2010 Census counts. Estimates of these demographic variables may vary in size and distribution compared to prior ACS years which were based on Census 2000 population counts. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB]. 

Beginning with the 2008 ACS questionnaire, the layout of the sex question response categories was changed to a horizontal side-by-side layout from a vertically stacked layout on the mail paper ACS questionnaire. For more information on differences in the questionnaire, see 2007 ACS Grid-Sequential Test report. 

Data from the 2010 ACS were controlled to independent estimates of the population by sex, age, race, and Hispanic origin that were based on the 2010 Census counts. Estimates of these demographic variables may vary in size and distribution compared to prior ACS years which were based on Census 2000 population counts. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The ACS question on race was revised in 2008 to make it consistent with the Census 2010 race question. Any change, compared with Census 2000, may be due to demographic changes, questionnaire changes, differences in ACS population controls, and/or methodological differences in the population estimates. 

Data from the 2010 ACS were controlled to independent estimates of the population by sex, age, race, and Hispanic origin that were based on the 2010 Census counts. Estimates of these demographic variables may vary in size and distribution compared to prior ACS years which were based on Census 2000 population counts. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

In addition, the observed changes between the 2009 ACS and the 2010 ACS race estimates may be attributed to a number of factors. Demographic change since 2009, which includes births and deaths in a geographic area and migration in and out of a geographic area, will have an impact on the resulting 2010 ACS estimates. Additionally, changes in race reporting patterns, as well as changes in the coding of race write-in responses and editing to follow 2010 Census guidelines may have influenced the results of the 2010 ACS. Also, while the ACS produces population, demographic and housing unit estimates, the 2010 Census provides the official race and Hispanic origin counts of the U.S. population and housing units.

An error was discovered in the processing of the 2009 ACS data for four of the detailed checkboxes within the Asian category (Japanese, Korean, Vietnamese, and Other Asian). These errors impact the data for the detailed Asian groups and, therefore, comparisons of the 2009 and 2010 estimates should be made with caution. Users may compare estimates for all other groups. 

The ACS question on Hispanic origin was revised in 2008 to make it consistent with the Census 2010 Hispanic origin question. Any change, compared with Census 2000, may be due to demographic changes, questionnaire changes, differences in ACS population controls, and/or methodological differences in the population estimates. 

Data from the 2010 ACS were controlled to independent estimates of the population by sex, age, race, and Hispanic origin that were based on the 2010 Census counts. Estimates of these demographic variables may vary in size and distribution compared to prior ACS years which were based on Census 2000 population counts. In addition, the 2010 ACS implemented a variety of new Hispanic origin coding changes to be consistent with the 2010 Census coding rules for Hispanic origin. These coding changes may have influenced the 2010 ACS Hispanic origin results. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

Ancestry is the only item for which a "not reported" category is published since missing ancestries are never assigned or allocated. The extent of missing ancestry answers was higher in Census 2000 than in the ACS. The difference in the level of response may contribute to the difference in the two distributions. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

In addition, the ancestry coding rules changed in 2010. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

Census 2000 represents data collected as of April 1, 2000 and thus the "2000" year of entry category accounts for the first quarter (Jan-Mar) in 2000 only. The ACS represents data collected throughout the entire year and thus the "2000" year of entry category accounts for the entire year of 2000. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The ACS asked for residence 1 year ago whereas Census 2000 asked for residence 5 years ago. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The ACS excludes taxicabs in the tabulation category of "public transportation" and includes them in the category "taxicab, motorcycle, bicycle or other means." However, Census 2000 includes taxicabs in the "public transportation" tabulation category. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The ACS used a joint relationship/marital status edit and Census 2000 did not. Also, Census 2000 provided more response categories because of a write-in option that was not used in the ACS. Differences in weighting schemes between the census and the ACS could produce inconsistencies in comparisons. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The ACS used a joint relationship/marital status edit and Census 2010 did not. The ACS also has a category for foster children which is not in Census 2010. Differences in weighting schemes between the census and the ACS could produce inconsistencies in comparisons.

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The ACS used a joint relationship/marital status edit and Census 2000 did not--these edits are used to determine categories of family types. Also, Census 2000 provided more response categories because of a write-in option that was not used in the ACS. Differences in weighting schemes between the census and the ACS could produce inconsistencies in comparisons.  

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The ACS used a joint relationship/marital status edit and Census 2010 did not. The ACS also has a category for foster children which is not in Census 2010. Differences in weighting schemes between the census and the ACS could produce inconsistencies in comparisons.  

Census 2000 had more detailed relationship categories than were available in the ACS to derive estimates of subfamilies. In addition, the weighting schemes that were used to produce the final estimated numbers of subfamilies were different.  

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The ACS used a joint relationship/marital status edit and Census 2000 did not. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The ACS reference period was 3 months preceding the date of interview, while the Census 2000 reference period was any time since February 1, 2000.

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The ACS has two separate categories for completing high school - "Regular high school diploma" and "GED or alternative credential". Census 2000 has only one category for completing high school - "HIGH SCHOOL GRADUATE - high school diploma or equivalent (for example: GED)". As a result, users may see differences in distributions when comparing Census 2000 to ACS data from 2008 and later years. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

In addition, the 2010 ACS field of degree codes differ slightly from 2009 ACS field of degree codes. Changes in the resulting distribution of field of degree are small but may be most impacted by the movement of general science from "Multi-Disciplinary Fields" to "Physical and Related Science Fields".  

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The ACS collects data throughout the year on an on-going, monthly basis and asks for a respondent's income over the "past 12 months" Census 2000, however, collected the income data for a fixed period of time -- "during 1999" (the last calendar year). For example, the 2010 ACS 1-year data reflect incomes over 2009-2010, the 2008-20010 ACS 3-year data reflect incomes over 2007-2010, and the 2006-2010 ACS 5-year data reflect incomes over 2005-2010. In a comparison study between Census 2000 income data and the 2000 ACS, income collected in Census 2000 was found to be about 4 percent higher than that in the 2000 ACS. For more information on the differences of income in the ACS and Census 2000, see Income in the American Community Survey: Comparisons to Census 2000. For specific questions and answers about sources of poverty data, see Questions and Answers about Sources of Poverty Data [PDF - <1.0 MB]. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

In addition, as ACS data are collected every month of the year, adjacent years will have some reference months in common. Hence, comparing the 2010 ACS 1-year with the 2009 ACS 1-year estimates is not an exact comparison of the economic conditions in 2010 with those in 2009. For a discussion of this and related issues, see Howard Hogan´s "Measuring Population Change Using the American Community Survey," in Applied Demography in the 21st Century (by Steven H. Murdock and David A. Swanson eds., Springer Netherlands, 2008). For specific questions and answers about sources of poverty data, see Questions and Answers about Sources of Poverty Data [PDF - <1.0 MB].

The ACS collects data throughout the year on an on-going, monthly basis and asks for a respondent's income over the "past 12 months." Census 2000, however, collected the income data for a fixed period of time -- "during 1999" (the last calendar year). For example, the 2010 ACS 1-year data reflect incomes over 2009-2010, the 2008-20010 ACS 3-year data reflect incomes over 2007-2010, and the 2006-2010 ACS 5-year data reflect incomes over 2005-2010. In a comparison study between Census 2000 income data and the 2000 ACS, income collected in Census 2000 was found to be about 4 percent higher than that in the 2000 ACS. For more information on the differences of income in the ACS and Census 2000, see Income in the American Community Survey: Comparisons to Census 2000. For specific questions and answers about sources of poverty data, see Questions and Answers about Sources of Poverty Data [PDF - <1.0 MB].  

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

In addition, as ACS data are collected every month of the year, adjacent years will have some reference months in common. Hence, comparing the 2010 ACS 1-year with the 2009 ACS 1-year estimates is not an exact comparison of the economic conditions in 2010 with those in 2009. For a discussion of this and related issues, see Howard Hogan´s "Measuring Population Change Using the American Community Survey," in Applied Demography in the 21st Century (by Steven H. Murdock and David A. Swanson eds., Springer Netherlands, 2008). For specific questions and answers about sources of poverty data, see Questions and Answers about Sources of Poverty Data [PDF - <1.0 MB].  

The 2010 ACS disability questions are different from the Census 2000 disability questions, thus comparisons cannot be made. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The 2010 ACS disability questions are different from the Census 2000 disability questions, thus comparisons cannot be made. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The 2010 ACS disability questions are different from the Census 2000 disability questions, thus comparisons cannot be made. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The ACS collects data throughout the year on an on-going, monthly basis and asks for a respondent's income over the "past 12 months." Census 2000, however, collected the income data for a fixed period of time -- "during 1999" (the last calendar year). For example, the 2010 ACS 1-year data reflect incomes over 2009-2010, the 2008-2010 ACS 3-year data reflect incomes over 2007-2010, and the 2006-2010 ACS 5-year data reflect incomes over 2005-2010. In a comparison study between Census 2000 income data and the 2000 ACS, income collected in Census 2000 was found to be about 4 percent higher than that in the 2000 ACS. For more information on the differences of income in the ACS and Census 2000, see Income in the American Community Survey: Comparisons to Census 2000. The Census Bureau recommends using CPI-U-RS adjustment factors published annually by the Bureau of Labor Statistics (BLS) to adjust 1999 median, mean, and per capita income dollar amounts shown in Summary File 3 to 2010 dollars by multiplying the 1999 dollar amounts by the CPI-U-RS factor of 1.30854107. For CPI-U-RS inflation adjustment factors for other years see: BLS Consumer Price Index. Furthermore, direct comparisons of income and earnings distributions between Census 2000 and the 2010 ACS are not possible due to inflation. Users interested in making distribution comparisons need to inflation adjust individual income records using the Public Use Microdata Samples (PUMS) files from Census 2000. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

In addition,as ACS data are collected every month of the year, adjacent years will have some reference months in common. Hence, comparing the 2010 ACS 1-year with the 2009 ACS 1-year estimates is not an exact comparison of the economic conditions in 2010 with those in 2009. For a discussion of this and related issues, see Howard Hogan´s "Measuring Population Change Using the American Community Survey," in Applied Demography in the 21st Century (by Steven H. Murdock and David A. Swanson eds., Springer Netherlands, 2008). For specific questions and answers about sources of poverty data, see Questions and Answers about Sources of Poverty Data [PDF - <1.0 MB].  

The ACS collects data throughout the year on an on-going, monthly basis and asks for a respondent's income over the "past 12 months." Census 2000, however, collected the income data for a fixed period of time -- "during 199" (the last calendar year). In a comparison study between Census 2000 income data and the 2000 ACS, income collected in Census 2000 was found to be about 4 percent higher than that in the 2000 ACS. For more information on the differences of income in the ACS and Census 2000, see Income in the American Community Survey: Comparisons to Census 2000. The Census Bureau recommends using CPI-U-RS adjustment factors published annually by the Bureau of Labor Statistics (BLS) to adjust 1999 median, mean, and per capita income dollar amounts shown in Summary File 3 to 2010 dollars by multiplying the 1999 dollar amounts by the CPI-U-RS factor of 1.30854107. For CPI-U-RS inflation adjustment factors for other years see: BLS Consumer Price Index. Furthermore, direct comparisons of income and earnings distributions between Census 2000 and the 2010 ACS are not possible due to inflation. Users interested in making distribution comparisons need to inflation adjust individual income records using the Public Use Microdata Samples (PUMS) files from Census 2000.  

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

In addition, as ACS data are collected every month of the year, adjacent years will have some reference months in common. Hence, comparing the 2010 ACS 1-year with the 2009 ACS 1-year estimates is not an exact comparison of the economic conditions in 2010 with those in 2009. For a discussion of this and related issues, see Howard Hogan´s "Measuring Population Change Using the American Community Survey," in Applied Demography in the 21st Century (by Steven H. Murdock and David A. Swanson eds., Springer Netherlands, 2008). For specific questions and answers about sources of poverty data, see Questions and Answers about Sources of Poverty Data [PDF - <1.0 MB]. 

Compare with Caution
The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note
Change in Population Controls [PDF - <1.0 MB].

In addition, as ACS data are collected every month of the year, adjacent years will have some reference months in common. Hence, comparing the 2010 ACS 1-year with the 2009 ACS 1-year estimates is not an exact comparison of the economic conditions in 2010 with those in 2009. For a discussion of this and related issues, see Howard Hogan´s "Measuring Population Change Using the American Community Survey," in Applied Demography in the 21st Century (by Steven H. Murdock and David A. Swanson eds., Springer Netherlands, 2008). For specific questions and answers about sources of poverty data, see Questions and Answers about Sources of Poverty Data [PDF - <1.0 MB].

Compare

Since Census 2000, the period of military service categories on the ACS questionnaire were updated to: 1) include the most recent period "September 2001 or later;" 2) list all "peace time" periods without showing a date-breakup in the list; and 3) update the Korean War and World War II dates to match the official dates as listed in US Code, Title 38. While the response categories differ slightly from those in Census 2000, data from the two questions can still be compared to one another.

Compare with Caution

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

Compare

The ACS has two separate questions, whereas in Census 2000, it was a two part question. However, the actual questions remain the same. 2010 ACS splits the answer category for the question: "Has this person ever served on active duty in the U.S. Armed Forces, military Reserves, or National Guard" into two more detailed categories. However, the data from this question can still be compared across these two survey years.

Compare with Caution

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

Compare with Caution

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

Compare with Caution

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

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The reference periods are different due to year-round ACS data collection. The ACS reference period is the week prior to the respondent completing the interview, or the field representative conducting the interview. Because questionnaires are mailed-out and field interviews are conducted throughout the year, there is a revolving reference period. For Census 2000, the reference period was the week prior to Census Day (April 1, 2000). The Census 2000 Summary File 3 (SF3) labor force data for some places where colleges are located appear to overstate the estimates of people in the labor force, the unemployed, and the percent unemployed because of data capture errors.

Compare with Caution

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

Compare

The ACS reference period is 12 months preceding the date of interview, while the Census 2000 reference period was the 1999 calendar year.

Compare with Caution

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

Compare

The ACS reference period is 12 months preceding the date of interview, while the Census 2000 reference period was the 1999 calendar year.

Compare with Caution

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

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The 2010 ACS Industry by Class of Worker tables combine "Unpaid family workers" with "Self-employed in own not incorporated business workers." The Census 2000 tables use different tabulation categories than the ACS. Also, the Census 2000 tables did not include the "full-time, year-round" population and there were no median earnings Class of Worker tables. Thus, comparisons cannot be made for this population or characteristic.

Compare with Caution

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

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Census 2000 codes are 3-digit codes and are based on the NAICS 1997. The 2010 ACS industry codes are 4-digit codes and are based on the 2007 NAICS. Codes and descriptions, particularly within the Electronic Shopping, Wholesale, and Information categories changed.

Compare with Caution

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

Compare with Caution

Census 2000 occupation codes are 3-digit codes based on Standard Occupation Classification (SOC) 2000. The 2010 ACS occupation codes are 4-digit codes based on SOC 2010. Codes and descriptions, particularly within the information technology, healthcare, printing, and human resources occupation categories changed. For a summary of 2010 code changes and a Census 2002 to 2010 occupation crosswalk, visit //www.census.gov/people/io/methodology/.

Compare with Caution

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note <br> <a href=">Change in Population Controls [PDF - <1.0 MB].

In addition, the 2009 ACS occupation codes are 4-digit codes based on Standard Occupation Classification (SOC) 2000. The 2010 ACS occupation codes are 4-digit codes based on SOC 2010. Codes and descriptions, particularly within the information technology, healthcare, printing, and human resources occupation categories changed. For a summary of 2010 code changes and a Census 2002 to 2010 occupation crosswalk, visit //www.census.gov/people/io/methodology/

Beginning in 2008, the ACS bedrooms question contained different wording and response options than the Census 2000 question. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

For Census 2000, tables were not released for total renter-occupied units. The universe in the ACS is "renter occupied" whereas in Census 2000 the universe was "specified renter-occupied housing units," thus comparisons cannot be made. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

For Census 2000, tables were not released for total renter-occupied units. The universe in the ACS is "renter occupied" whereas in Census 2000, the universe was "specified renter-occupied housing units," thus comparisons cannot be made. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

Changes made between 2007 and 2008 to the ACS question wording as well as the response option resulted in an increase in the "Lacking Kitchen Facilities" category compared with pre-2008 ACS and Census 2000. For more details, see Errata #53. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

With a mortgage/without a mortgage released in Census 2000 for both total owner-occupied units and specified owner-occupied units. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

Beginning in 2008, the ACS rooms question contained different wording and response options than the Census 2000 question. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

For Census 2000, tables with full distribution were released for total owner-occupied units but medians were not shown. When available, compare like universes. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

Changes made between 2007 and 2008 to the ACS question wording as well as the response option resulted in an increase in the "Lacking Plumbing Facilities" category compared with pre-2008 ACS and Census 2000. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The universe in the ACS is "owner occupied" whereas in Census 2000, the universe was "specified owner-occupied housing units," thus comparisons cannot be made. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

Beginning in 2008, the ACS rooms question contained different wording and response options than the Census 2000 question.  

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

For Census 2000, tables with full distributions were released for total owner-occupied units but medians were not shown. When available, compare like universes. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

In 2008, there was a change in the wording and response options for the the ACS question on telephone service. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The tabulation category "Rented or sold, not occupied" in Census 2000 is separated into two categories "Rented, not occupied" and "Sold, not occupied" in the ACS. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

Because the 2010 Census and the American Community Survey differ in their design and data collection methods, users should note that estimates of vacancy rates may also differ. For more information on vacancy rates in the 2010 Census and ACS, visit the ACS User Note or preliminary results report. 

Unlike Census 2000, the ACS allowed a write-in for values over $250,000 until 2007. Beginning in 2008, value was collected as a continuous variable. For Census 2000, tables with full distribution, medians, and aggregate values were released for both specified owner-occupied units as well as total owner-occupied units. ACS only releases tables for total owner-occupied units. When making comparisons users should compare like universes. 

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].

The total group quarters (GQ) population in the ACS may not be comparable with Census 2000 because: 1) There are some Census 2000 GQ types that were out of scope in the ACS such as domestic violence shelters and soup kitchens. Also, there are some Census 2000 GQ type categories that are no longer valid (residential care facility providing "Protective Oversight," hospitals/wards for the chronically ill and hospitals/wards for drug/alcohol abuse). The exclusion of these GQ types from the ACS may result in a small bias in some ACS estimates to the extent that the excluded population is different from the included population. 2) A sample of GQ facilities throughout the United States and Puerto Rico were selected for the ACS. ACS controls the GQ sample at the state level only. Therefore, for lower levels of geography, particularly when there are relatively few GQs in a geographic area, the ACS estimate of the GQ population may vary from the estimate from Census 2000. 

The group quarters data from the 2010 ACS were controlled to independent estimates based on the 2010 Census counts. Estimates of the group quarters population may vary in size and distribution compared to prior ACS years which were based on Census 2000 population counts. The weighting for the group quarters (GQ) population is controlled at the state level, but not at sub-state levels. For this reason, users may observe greater fluctuations in year-to-year ACS estimates of the GQ population at sub-state levels than at state levels. The causes of these fluctuations typically are the result of either GQs that have closed or where the current population of the GQ is significantly different than the expected population as reflected on the sampling frame. Substantial changes in the ACS GQ estimates can impact ACS estimates of total population characteristics for areas where either the GQ population is a substantial proportion of the total population or where the GQ population may have very different characteristics than the total population as a whole. Users can assess the impact that year-to-year changes in sub-state GQ total population estimates have on the changes in total ACS population estimates by accessing Table B26001 on American Fact Finder. Users should also use their local knowledge to help determine whether the year-to-year change in the ACS estimate represents a real change in the GQ population or may be the result of the lack of adequate population controls for sub-state areas. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].  

The ACS group quarters (GQ) population at sub-state levels may not be comparable to the 2010 Census data. The weighting for the group quarters (GQ) population is controlled at the state level, but not at sub-state levels. For this reason, users may observe larger differences between the ACS and 2010 Census population at sub-state levels than at state levels. The causes of these differences typically are the result of either GQs that have closed or where the current population of the GQ is significantly different than the expected population as reflected on the sampling frame. Substantial changes in the ACS GQ estimates can impact ACS estimates of total population characteristics for areas where either the GQ population is a substantial proportion of the total population or where the GQ population may have very different characteristics than the total population as a whole.

The 2009 ACS and 2010 ACS 1-year estimates use different Census base years for the population estimates used in the ACS weighting. Estimates of population size are not comparable between 2009 and 2010. Estimates of percent distributions, rates, and ratios should be compared with caution. For more details, visit the ACS Research Note Change in Population Controls [PDF - <1.0 MB].