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

Beginning in 1999, the American Community Survey questions differ from the 1996-1998 questions only in the format of the skip instructions. Beginning in 2004, the category, "Public transportation" was tabulated to exclude workers who used taxicab as their means of transportation.

Data on language spoken at home were derived from answers to the 2006 American Community Survey Questions 13a and 13b. These questions were asked only of persons 5 years of age and older. Instructions mailed with the American Community Survey questionnaire instructed respondents to mark "Yes" on Question 13a if they sometimes or always spoke a language other than English at home, and "No" if a language was spoken only at school - or if speaking was limited to a few expressions or slang. For Question 13b, respondents printed the name of the non-English language they spoke at home. If the person spoke more than one non-English language, they reported the language spoken most often. If the language spoken most frequently could not be determined, the respondent reported the language learned first.
Questions 13a and 13b referred to languages spoken at home in an effort to measure the current use of languages other than English. This category excluded respondents who spoke a language other than English exclusively outside of the home.
Most respondents who reported speaking a language other than English also spoke English. The questions did not permit a determination of the primary language of persons who spoke both English and another language.
An automated computer system coded write-in responses to Question 13b into more than 380 detailed language categories. This automated procedure compared write-in responses with a master computer code list - which contained approximately 55,000 previously coded language names and variants - and then assigned a detailed language category to each write-in response. The computerized matching assured that identical alphabetic entries received the same code. Clerical coding categorized any write-in responses that did not match the computer dictionary. When multiple languages other than English were specified, only the first was coded.
The write-in responses represented the names people used for languages they spoke. They may not have matched the names or categories used by professional linguists. The categories used were sometimes geographic and sometimes linguistic. The following table provides an illustration of the content of the classification schemes used to present language data.
Four and Thirty-Nine Group Classifications of Languages Spoken at Home with Illustrative Examples

Four-Group Classification	Thirty-nine Group Classification	Examples
Spanish	Spanish or Spanish Creole	Spanish, Ladino, Pachuco
Other Indo-European languages	French	French, Cajun, Patois
	French Creole	Haitian Creole
	Italian	Italian
	Portuguese or Portuguese Creole	Portuguese, Papia Mentae
	German	German, Luxembourgian
	Yiddish	Yiddish
	Other West Germanic languages	Dutch, Pennsylvania Dutch, Afrikaans
	Scandinavian languages	Danish, Norwegian, Swedish
	Greek	Greek
	Russian	Russian
	Polish	Polish
	Serbo-Croatian	Serbo-Croatian, Croatian, Serbian
	Other Slavic languages	Czech, Slovak, Ukrainian
	Armenian	Armenian
	Persian	Persian
	Gujarathi	Gujarathi
	Hindi	Hindi
	Urdu	Urdu
	Other Indic languages	Bengali, Marathi, Punjabi, Romany
	Other Indo-European languages	Albanian, Gaelic, Lithuanian,Rumanian
Asian and Pacific Island languages	Chinese	Cantonese, Formosan, Mandarin
	Japanese	Japanese
	Korean	Korean
	Mon-Khmer, Cambodian	Mon-Khmer, Cambodian
	Hmong	Hmong
	Thai	Thai
	Laotian	Laotian
	Vietnamese	Vietnamese
	Other Asian languages	Dravidian languages (Malayalam, Telugu, Tamil),Turkish
	Tagalog	Tagalog
	Other Pacific Island languages	Chamorro, Hawaiian, Ilocano, Indonesian, Samoan
All other languages	Navajo	Navajo
	Other Native North American languages	Apache, Cherokee, Dakota, Pima, Yupik
	Hungarian	Hungarian
	Arabic	Arabic
	Hebrew	Hebrew
	African languages	Amharic, Ibo, Twi, Yoruba, Bantu, Swahili, Somali
	Other and unspecified languages	Syriac, Finnish, Other languages of the Americas, not reported

In households where one or more people spoke a language other than English, the household language assigned to all household members was the non-English language spoken by the first person with a non-English language. This assignment scheme ranked household members in the following order: householder, spouse, parent, sibling, child, grandchild, other relative, stepchild, unmarried partner, housemate or roommate, and other nonrelatives. Therefore, a person who spoke only English may have had a non-English household language assigned during tabulations by household language.

Respondents who reported speaking a language other than English were asked to indicate their English-speaking ability based on one of the following categories: "Very well," "Well," "Not well," or "Not at all." Ideally, the data on ability to speak English represented a person's perception of their own English-speaking ability. However, because one household member usually completes American Community Survey questionnaires, the responses may have represented the perception of another household member. Respondents were not instructed on how to interpret the response categories in Question 13c.

A linguistically isolated household was one in which all adults had some limitation in communicating English. A household was classified as "linguistically isolated" if, 1.) No household member age 14 years and over spoke only English, and 2). No household member age 14 years and over who spoke another language spoke English "Very well." All members of a linguistically isolated household were tabulated as "linguistically isolated," including members under 14 years old who may have spoken only English.

The language question is about current use of a non-English language, not about ability to speak another language or the use of such a language in the past. People who speak a language other than English outside of the home are not reported as speaking a language other than English. Similarly, people whose mother tongue is a non-English language but who do not currently use the language at home do not report the language. Some people who speak a language other than English at home may have first learned that language in school. These people are expected to indicate speaking English "Very well."
The detail in which language names are coded may give a false impression of the linguistic precision of these data. The identifying names used by speakers of a language may reflect ethnic, geographic, or political affiliations, and are not necessarily identical to official linguistic distinctions.
Although there are more than 6,000 languages in the world, the Census Bureau codes all reported languages into approximately 380 categories.

- Limitation of the Data -Beginning in 2006, the population in group quarters (GQ) is included in the ACS. Some types of GQ populations may have ability to speak English and language spoken at home distributions that are different from the household population. The inclusion of the GQ population could therefore have a noticeable impact on the ability to speak English and language spoken at home distribution. This is particularly true for areas with a substantial GQ population.

The minor changes in specific codes starting in 1999 do not affect the tabulations of languages. The list of examples was moved below the write-in 1999; in the 1996-1998 ACS questionnaires, it was directly after the question.

The data on place of work is related to a reference week, that is, the calendar week preceding the date on which the respondents completed their questionnaires or were interviewed. This week is not the same for all respondents because data were collected over a 12-month period. The lack of a uniform reference week means that the place-of-work data reported in the survey will not exactly match the distribution of workplace locations observed or measured during an actual workweek. The place-of-work data are estimates of people 16 years and over who were both employed and at work during the reference week (including people in the Armed Forces). People who did not work during the reference week but had jobs or businesses from which they were temporarily absent due to illness, bad weather, industrial dispute, vacation, or other personal reasons are not included in the place-of-work data. Therefore, the data on place of work understate the total number of jobs or total employment in a geographic area during the reference week. It also should be noted that people who had irregular, casual, or unstructured jobs during the reference week might have erroneously reported themselves as not working. The address where the individual worked most often during the reference week was recorded on the questionnaire. If a worker held two jobs, only data about the primary job (the job where one worked the greatest number of hours during the preceding week) was requested. People who regularly worked in several locations during the reference week were requested to give the address at which they began work each day. For cases in which daily work was not begun at a central place each day, the respondent was asked to provide as much information as possible to describe the area in which he or she worked most during the reference week.
Since both the American Community Survey and the decennial censuses are related to a "reference week" that has some variability, the data do not reflect any single week. Since the American Community Survey data are collected over 12 months, the reference week in American Community Survey has a greater range of variation. (See "Reference Week.")

Starting in 1999, the American Community Survey questions differ from the 1996-1998 questions in that the labels on the write-in spaces were modified to provide clarifications. The 2004 American Community Survey marked the first time that workplace-based tables were released as a part of a standard census data product.