Using models of disability from the Institute of Medicine and the International Classification of Functioning, disability is defined as the restriction in participation that results from a lack of fit between the individual's functional limitations and the characteristics of the physical and social environment. So while the disability is not seen as intrinsic to the individual, the way to capture it in a survey is to measure components that make up the process. The American Community Survey identifies serious difficulty in four basic areas of functioning: vision, hearing, ambulation, and cognition. Described below, the ACS asks respondents about serious difficulty and the resulting data can be used individually or combined. The ACS also includes two questions to identify people with difficulties that might impact their ability to live independently. In the 2006 American Community Survey, there are three disability questions, two with subparts totaling six questions in all, as described below.

Beginning in 2006, the population in group quarters (GQ) is included in the ACS. The universe for most disability data tabulations is the civilian noninstitutionalized population. Some types of GQ populations have disability distributions that are different from the household population. The inclusion of the noninstitutionalized GQ population could therefore have a noticeable impact on the disability distribution. This is particularly true for areas with a substantial noninstitutionalized GQ population. For example, the number of people with a disability may increase in areas having a substantial group home population. In areas having a substantial college dormitory population, the percentage of people with a disability may decrease because the base of the percentage, which now includes the population in college dormitories, is larger.

The data on sensory and physical limitations were derived from answers to Questions 15a and 15b, which were asked of people 5 years old and over. Questions 15a and 15b asked respondents if they had any of the following two long-lasting conditions: "Blindness, deafness, severe vision or hearing impairment," or "A condition that substantially limits one or more basic physical activities such as walking, climbing stairs, reaching, lifting, or carrying." Respondents were instructed to mark "yes" or "no" for each long-lasting condition. Question 15a is labeled as "Sensory disability" and Question 15b as "Physical disability" for some of the disability data products such as the ACS Detailed Tables.

For the 1996-1998 American Community Survey, the question, which was asked of persons 5 years old and over, instructed the respondents to mark each appropriate box if they had difficulty with any of the following three specific functions: "Difficulty seeing (even with glasses)," "Difficulty hearing (even with a hearing aid)," or "Difficulty walking." The respondents could mark as many as three boxes depending on their functional limitation status. If the respondents did not have difficulty with any of the three specific functions, the question instructed them to mark the box labeled "None of the above." The sensory and physical disability data obtained from the 1996-1998 American Community Survey are not comparable to data collected from the 1999-2006 American Community Surveys.

¹Note that all references to the small GQ stratum include both small GQs and GQs closed on Census day.

No comparable data on cognitive functioning were obtained in the 1996-1998 American Community Survey. This question was introduced in the 1999 American Community Survey.

The data on self-care limitations were derived from answers to Question 16b, which was asked of people 5 years and over. The question asked respondents if they had a physical, mental, or emotional condition lasting 6 months or more that made it difficult "dressing, bathing, or getting around inside the home." Respondents were instructed to mark "yes" or "no." Question 16b is labeled as "Self-Care Disability" for some disability data products such as the ACS Detailed Tables.

No comparable data on self-care limitations were obtained in the 1996-1998 American Community Survey. This question was introduced in the 1999 American Community Survey.

The data on mobility limitations were derived from answers to Question 17a. Although Question 17a was asked of people 15 years and over, the data products only report this type of disability for people 16 years and over. The question asked respondents if they had a physical, mental, or emotional condition lasting 6 months or more that made it difficult "going outside the home alone to shop or visit a doctor's office." Respondents were instructed to mark "yes" or "no." Question 17a is labeled as "Go-outside-home Disability" for some disability products such as the ACS Detailed Tables.

A measure obtained by dividing the number of people living in occupied housing units by the total number of occupied housing units. This measure is rounded to the nearest hundredth.

A measure obtained by dividing the number of people living in owner-occupied housing units by the total number of owner-occupied housing units. This measure is rounded to the nearest hundredth.

A measure obtained by dividing the number of people living in renter-occupied housing units by the total number of renter-occupied housing units. This measure is rounded to the nearest hundredth.

The Census Bureau does not recommend trend analysis using the 2003-2006 data with years prior to 2003 due to the 2003 questionnaire change. For more information regarding the 2003 questionnaire change, view "Disability Data From the American Community Survey: A Brief Examination of the Effects of a Question Redesign in 2003" ( http://www.census.gov/hhes/www/disability/ACS_disability.pdf).

For the 1996-1998 American Community Survey, the data on going-outside-home limitations were derived from answers to Question 16a, which was asked of persons 16 years old and over. The question was slightly different from the 1999-2002 question and asked the respondents if they had a long-lasting physical or mental condition that made it difficult to "go outside the home alone to shop or visit a doctor's office." In the 1999-2002 American Community Survey, the going-outside-home question was part of Question 16. The 2003 questionnaire moved go-outside-home limitations to Question 17a and introduced a new skip instruction between Questions 16 and 17.

The review process involves both review of the editing process and a reasonableness review. After editing and imputation are complete, Census Bureau subject matter analysts review the resulting data files. The files contain both unedited and edited data, together with the accompanying imputation flag variables that indicate which missing, inconsistent, or incomplete items have been filled by imputation methods. Subject matter analysts first compare the unedited and edited data to see that the edit process worked as intended. The subject analysts also undertake their own analyses, looking for problems or inconsistencies in the data from their perspectives. When conducting the initial edit review, they determine whether the results make sense through a process known as a reasonableness review. If year-to-year changes do not appear to be reasonable, they institute a more comprehensive review to reexamine and resolve the issues. Allocation rates from the current year are compared with previous years to check for notable differences. A reasonableness review is done by topic, and results on unweighted data are compared across years to see if there are substantial differences. The initial reasonableness review takes place with national data, and another final review compares data from smaller geographic areas, such as counties and states (Jiles, 2007).

These processes also are carried out after weighting and swapping data (discussed in Chapter 12). Analysts also examine unusual individual cases that were changed during editing to ensure accuracy and reasonableness.

The analysts also use a number of special reports for comparisons based on the edit outputs and multiple years of survey data. These reports and data are used to help isolate problems in specifications or processing. They include detailed information on imputation rates for all data items, as well as tallies representing counts of the number of times certain programmed logic checks were executed during editing. If editing problems are discovered in the data during this review process, it is often necessary to rerun the programs and repeat the review.

Once the subject matter analysts have approved data within the edited files, and their associated recodes, the files are ready to serve as inputs to the data products processing operation. If errors attributable to editing problems are detected during the creation of data products, it may be necessary to repeat the editing and review processes.

Median fire, hazard, and flood insurance divides the fire, hazard, and flood insurance distribution into two equal parts: one-half of the cases falling below the median fire, hazard, and flood insurance and one-half above the median. Median fire, hazard, and flood insurance is computed on the basis of a standard distribution (see the "Standard Distributions" section under "Derived Measures.") Median fire, hazard, and flood insurance is rounded to the nearest whole dollar. (For more information on medians, see "Derived Measures.")

The American Community Survey questions have been the same since 1996.

The data on employment limitations were derived from answers to Question 17b. Although it was asked of people 15 years and over, the data products only report this type of disability for people aged 16 to 64. The question asked the respondents if they had a physical, mental, or emotional condition lasting 6 months or more that made it difficult "working at a job or business." Respondents were instructed to mark "yes" or "no." Question 17b is labeled as "Employment Disability" for some disability data products such as the ACS Detailed Tables.

For the 1996-1998 American Community Survey, the data on employment limitations were derived from answers to Question 16b, which was asked of persons 16 years old and over. The question was slightly different from the 1999-2003 question and asked the respondents if they had a long-lasting physical or mental condition that "prevents this person from working at a job or business." In the 1999-2002 American Community Survey, the employment limitations question was part of Question 16. The 2003 questionnaire moved the employment limitations to Question 17b and introduced a new skip instruction between Questions 16 and 17.

The Census Bureau does not recommend trend analysis using the 2003-2006 data with years prior to 2003 due to the 2003 questionnaire change. For more information regarding the 2003 questionnaire change, view "Disability Data From the American Community Survey: A Brief Examination of the Effects of a Question Redesign in 2003" ( http://www.census.gov/hhes/www/disability/ACS_disability.pdf).

The Census Bureau uses the six disability questions above to determine an individual's disability status in some of its data products such as in the ACS Detailed Tables and the Disability Profile. People aged 16 to 64 were classified as having a disability if they reported at least one of the above six limitations. People aged 5 to 15 were classified as having a disability if they reported any one of the four limitations: sensory disability, physical disability, mental disability, or self-care disability. People 65 and over were classified as having a disability if they reported any one of the five limitations: sensory disability, physical disability, mental disability, self-care disability, or going-outside-home disability.

Since two of the six questions used to determine disability status are no longer comparable with those of the prior years, the Census Bureau does not recommend trend analysis using the 2003-2006 data with years prior to 2003. For more information regarding the 2003 questionnaire change, view "Disability Data from the American Community Survey: A Brief Examination of the Effects of a Question Redesign in 2003" ( http://www.census.gov/hhes/www/disability/ACS_disability.pdf).

Data on school enrollment and grade or level attending were derived from answers to Question 10. People were classified as enrolled in school if they were attending a "regular" public or private school or college at any time during the 3 months prior to the time of interview. The question included instructions to "include only nursery or preschool, kindergarten, elementary school, and schooling which leads to a high school diploma, or a college degree" as regular school or college. Respondents who did not answer the enrollment question were assigned the enrollment status and type of school of a person with the same age, sex, race, and Hispanic or Latino origin whose residence was in the same or nearby area.
A regular school advances a person toward an elementary school certificate, a high school diploma, or a college, university, or professional school (such as law or medicine) degree. Tutoring or correspondence schools are included if credit can be obtained in a "regular school." People enrolled in "vocational, technical, or business school" were not reported as enrolled in regular school. Field interviewers were instructed to classify individuals who were home schooled as enrolled in private school. The guide sent out with the mail questionnaire does not include explicit instructions for how to classify home schoolers.

Includes people who attended school in the reference period and indicated they were enrolled by marking one of the questionnaire categories for "public school, public college," or "private school, private college." The instruction guide defines a public school as "any school or college controlled and supported primarily by a local, county, state, or federal government." Private schools are defined as schools supported and controlled primarily by religious organizations or other private groups. Respondents who marked both the "public" and "private" boxes are edited to the first entry, "public."

Data on school enrollment also are collected and published by other federal, state, and local government agencies. Because these data are obtained from administrative records of school systems and institutions of higher learning, they are only roughly comparable to data from population censuses and surveys. Differences in definitions and concepts, subject matter covered, time references, and data collection methods contribute to the differences in estimates. At the local level, the difference between the location of the institution and the residence of the student may affect the comparability of census and administrative data because census data are collected from and based on a respondent's residence. Differences between the boundaries of school districts and census geographic units also may affect these comparisons.

Since 1999, the American Community Survey refers to "regular school or college," while the 1996-1998 American Community Survey did not restrict reporting to "regular" school, and contained an additional category for the "vocational, technical or business school."

From 1999-2006, in the American Community Survey, people reported to be enrolled in "public school, public college" or "private school, private college" were classified by grade or level according to responses to Question 10b, "What grade or level was this person attending?" Seven levels were identified: "nursery school, preschool;" "kindergarten;" elementary "grade 1 to grade 4" or "grade 5 to grade 8;" high school "grade 9 to grade 12;" "college undergraduate years (freshman to senior);" and "graduate or professional school ( for example: medical, dental, or law school )."

Beginning in 2006, the population universe in the American Community Survey includes people living in group quarters. Data users may see slight differences in levels of school enrollment in any given geographic area due to the inclusion of this population. The extent of this difference, if any, depends on the type of group quarters present and whether the group quarters population makes up a large proportion of the total population. For example, in areas that are home to several colleges and universities, the percent of individuals 18 to 24 who were enrolled in college or graduate school would increase, as people living in college dormitories are now included in the universe.

The 1996-1998 American Community Survey used the educational attainment question to estimate level of enrollment for those reported to be enrolled in school, and had a single year write-in for the attainment of grades 1 through 11. Grade levels estimated using the attainment question were not consistent with other estimates, so a new question specifically asking grade or level of enrollment was added starting with the 1999 American Community Survey questionnaire.

Data on educational attainment were derived from answers to Question 11, which was asked of all respondents. Educational attainment data are tabulated for people 18 years old and over. Respondents are classified according to the highest degree or the highest level of school completed. The question included instructions for persons currently enrolled in school to report the level of the previous grade attended or the highest degree received.
The educational attainment question included a response category that allowed people to report completing the 12th grade without receiving a high school diploma. Respondents who received a high school diploma or the equivalent (for example, passed the test of General Educational Development (G.E.D.)), and did not attend college, were instructed to report "high school graduate." "Some college" is in two categories: "Some college credit, but less than 1 year" and "1 or more years of college, no degree." The category "Associate's degree" included people whose highest degree is an associate's degree, which generally requires 2 years of college level work and is either in an occupational program that prepares them for a specific occupation, or an academic program primarily in the arts and sciences. The course work may or may not be transferable to a bachelor's degree. Master's degrees include the traditional MA and MS degrees and field-specific degrees, such as MSW, MEd, MBA, MLS, and MEng. Instructions included in the respondent instruction guide provided the following examples of professional school degrees: Medicine, dentistry, chiropractic, optometry, osteopathic medicine, pharmacy, podiatry, veterinary medicine, law, and theology. The order in which degrees were listed suggested that doctorate degrees were "higher" than professional school degrees, which were "higher" than master's degrees. If more than one box was filled, the response was edited to the highest level or degree reported.
The instructions further specified that schooling completed in foreign or ungraded school systems should be reported as the equivalent level of schooling in the regular American system. The instructions specified that certificates or diplomas for training in specific trades or from vocational, technical or business schools were not to be reported. Honorary degrees awarded for a respondent's accomplishments were not to be reported.

This category includes people whose highest degree was a high school diploma or its equivalent, people who attended college but did not receive a degree, and people who received an associates, bachelors, masters, or professional or doctorate degree. People who reported completing the 12th grade but not receiving a diploma are not included.

This category includes people of compulsory school attendance age or above who were not enrolled in school and were not high school graduates. These people may be referred to as "high school dropouts." There is no restriction on when they "dropped out" of school; therefore, they may have dropped out before high school and never attended high school.

Beginning in 2006, the population in group quarters (GQ) is included in the ACS. Some types of GQ populations may have educational attainment distributions that are different from the household population. The inclusion of the GQ population could therefore have a noticeable impact on the educational attainment distribution. This is particularly true for areas with a substantial GQ population.

Since 1999, the American Community Survey question does not have the response category for "Vocational, technical, or business school degree" that the 1996-1998 American Community Surveys question had. Starting in 1999, the American Community Survey question had two categories for some college: "Some college credit, but less than 1 year" and "1 or more years of college, no degree." The 1996-1998 American Community Survey question had one category: "Some college but no degree."
In the 1996-1998 American Community Survey, the educational attainment question was used to estimate level of enrollment. Since 1999, a question regarding grade of enrollment was included.
Since 1999, the American Community Survey attainment question grouped grade categories below high school into the following three categories: "Nursery school to 4th grade," "5th grade or 6th grade," and "7th grade or 8th grade." The 1996-1998 American Community Survey question allowed a write-in for highest grade completed for grades 1-11 in addition to "Nursery or preschool" and "Kindergarten."

The data on age were derived from answers to Question 2. The age classification is based on the age of the person in complete years at the time of interview. Both age and date of birth are used in combination to calculate the most accurate age at the time of the interview. Inconsistently reported and missing values are assigned or imputed based on the values of other variables for that person, from other people in the household, or from people in other households ("hot deck" imputation). Data on age are used to determine the applicability of other questions for a particular individual and to classify other characteristics in tabulations. Age data are needed to interpret most social and economic characteristics used to plan and analyze programs and policies. Therefore, age data are tabulated by many different age groupings, such as 5-year age groups.

The median age is the age that divides the population into two equal-size groups. Half of the population is older than the median age and half is younger. Median age is based on a standard distribution of the population by single years of age and is shown to the nearest tenth of a year. (See the sections on "Standard Distributions" and "Medians" under "Derived Measures.")

The age dependency ratio is derived by dividing the combined under-18 and 65-and-over populations by the 18-to-64 population and multiplying by 100.

The old-age dependency ratio is derived by dividing the population 65 years and over by the 18-to-64 population and multiplying by 100.

The child dependency ratio is derived by dividing the population under 18 years by the 18-to-64 population, and multiplying by 100.

Caution should be taken when comparing population in age groups across time. The entire population continually ages into older age groups over time and babies fill in the youngest age group. Therefore, the population of a certain age is made up of a completely different group of people in 2000 and 2006. 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 the 2006 ACS. For example, Baby Boomers were age 36 to 54 in Census 2000 while they were age 44 to 62 in the 2006 ACS. Therefore, the age group 55 to 59 would show a considerable increase in population when comparing Census 2000 data with the 2006 ACS data.
Beginning in 2006, the population in group quarters (GQ) is included in the ACS. Some types of GQ populations have age distributions that are very different from the household population. The inclusion of the GQ population could therefore have a noticeable impact on the age distribution. This is particularly true for areas with a substantial GQ population.

The 1996-2002 American Community Survey question asked for month, day, and year of birth before age. Since 2003, the American Community Survey question asked for age, followed by month, day, and year of birth. In 2006, an additional instruction was provided with the age and date of birth question on the American Community Survey questionnaire to report babies as age 0 when the child was less than 1 year old. The addition of this instruction occurred after 2005 National Census Test results indicated increased accuracy of age reporting for babies less than one year old.