The data on weeks worked in 1999 were derived from answers to long-form questionnaire Item 30b, which was asked of people 15 years old and over who indicated in long-form questionnaire Item 30a that they worked in 1999. The data were tabulated for people 16 years old and over and pertain to the number of weeks during 1999 in which a person did any work for pay or profit (or took paid vacation or paid sick leave) or worked without pay on a family farm or in a family business. Weeks on active duty in the armed forces also are included as weeks worked.

Median weeks worked in 1999 divides the weeks worked distribution into two equal parts: one-half of the cases falling below the median weeks worked and one-half above the median. Median weeks worked in 1999 is computed on the basis of a standard distribution (see the "Standard Distributions" section under "Derived Measures"). Median weeks worked is rounded to the nearest whole number. (For more information on medians, see "Derived Measures".)

The data on usual hours worked in 1999 were derived from answers to long-form questionnaire Item 30c. This question was asked of people 15 years old and over who indicated that they worked in 1999 in Question 30a, and the data are tabulated for people 16 years old and over. The respondent was asked to report the number of hours usually worked during the weeks worked in 1999. If their hours varied considerably from week to week during 1999, the respondent was asked to report an approximate average of the hours worked each week. People 16 years old and over who reported that they usually worked 35 or more hours each week are classified as "Usually worked full time"; people who reported that they usually worked 1 to 34 hours each week are classified as "Usually worked part time."

Median usual hours worked per week in 1999 divides the usual hours worked distribution into two equal parts: one-half of the cases falling below the median usual hours worked and one-half above the median. Median usual hours worked per week in 1999 is computed on the basis of a standard distribution (see the "Standard Distributions" section under "Derived Measures"). Median usual hours worked per week is rounded to the nearest whole hour. (For more information on medians, see "Derived Measures".)

The aggregate usual hours worked per week in 1999 is the number obtained by summing across the usual hours worked values of all people who worked in 1999. (Note that there is one usual hours value for each worker, so the number of items summed equals the number of workers.)

Mean usual hours worked per week is calculated by dividing the aggregate number of usual hours worked per week worked in 1999 by the total number of people who worked in 1999. Mean usual hours worked per week is rounded to the nearest tenth. (For more information on means, see "Derived Measures".)

'Full-time, year-round workers' consists of people 16 years old and over who usually worked 35 hours or more per week for 50 to 52 weeks in 1999. The term "worker" in these concepts refers to people classified as Worked in 1999 as defined above. The term worked in these concepts means "worked one or more weeks in 1999" as defined above under "Weeks Worked in 1999."

It is probable that data on the number of people who worked in 1999 and on the number of weeks worked are understated since there was probably a tendency for respondents to forget intermittent or short periods of employment or to exclude weeks worked without pay. There may also have been a tendency for people not to include weeks of paid vacation among their weeks worked, which would result in an underestimate of the number of people who worked "50 to 52 weeks."

The data on weeks worked collected in Census 2000 are comparable with data from the 1960 to 1990 censuses, but may not be entirely comparable with data from the 1940 and 1950 censuses. Starting with the 1960 census, two separate questions have been used to obtain this information. The first identifies people with any work experience during the year and, thus, indicates those people for whom the question about number of weeks worked applies. In 1940 and 1950, the questionnaires contained only a single question on number of weeks worked. In 1970, people responded to the question on weeks worked by indicating one of six weeks-worked intervals. In 1980 and 1990, people were asked to enter the specific number of weeks they worked.

The terms "worker" and "work" appear in connection with several subjects: employment status, journey-to-work, class of worker, and work status in 1999. Their meaning varies and, therefore, should be determined by referring to the definition of the subject in which they appear. When used in the concepts "Workers in Family," "Workers in Family in 1999," and "Full-Time, Year-Round Workers," the term "worker" relates to the meaning of work defined for the "Work Status in 1999" subject.

A measure derived by dividing the total number of males by the total number of females, and then multiplying by 100. This measure is rounded to the nearest tenth.

A question on the sex of individuals has been included in every census. Census 2000 was the first time that first name was used for imputation of cases where sex was not reported.

1. White; Black or African American
2. White; American Indian and Alaska Native
3. White; Asian
4. White; Native Hawaiian and Other Pacific Islander
5. White; Some other race
6. Black or African American; American Indian and Alaska Native
7. Black or African American; Asian
8. Black or African American; Native Hawaiian and Other Pacific Islander
9. Black or African American; Some other race
10. American Indian and Alaska Native; Asian
11. American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander
12. American Indian and Alaska Native; Some other race
13. Asian; Native Hawaiian and Other Pacific Islander
14. Asian; Some other race
15. Native Hawaiian and Other Pacific Islander; Some other race
16. White; Black or African American; American Indian and Alaska Native
17. White; Black or African American; Asian
18. White; Black or African American; Native Hawaiian and Other Pacific Islander
19. White; Black or African American; Some other race
20. White; American Indian and Alaska Native; Asian
21. White; American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander
22. White; American Indian and Alaska Native; Some other race
23. White; Asian; Native Hawaiian and Other Pacific Islander
24. White; Asian; Some other race
25. White; Native Hawaiian and Other Pacific Islander; Some other race
26. Black or African American; American Indian and Alaska Native; Asian
27. Black or African American; American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander
28. Black or African American; American Indian and Alaska Native; Some other race
29. Black or African American; Asian; Native Hawaiian and Other Pacific Islander
30. Black or African American; Asian; Some other race
31. Black or African American; Native Hawaiian and Other Pacific Islander; Some other race
32. American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander
33. American Indian and Alaska Native; Asian; Some other race
34. American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander; Some other race
35. Asian; Native Hawaiian and Other Pacific Islander; Some other race
36. White; Black or African American; American Indian and Alaska Native; Asian
37. White; Black or African American; American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander
38. White; Black or African American; American Indian and Alaska Native; Some other race
39. White; Black or African American; Asian; Native Hawaiian and Other Pacific Islander
40. White; Black or African American; Asian; Some other race
41. White; Black or African American; Native Hawaiian and Other Pacific Islander; Some other race
42. White; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander
43. White; American Indian and Alaska Native; Asian; Some other race
44. White; American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander; Some other race
45. White; Asian; Native Hawaiian and Other Pacific Islander; Some other race
46. Black or African American; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander
47. Black or African American; American Indian and Alaska Native; Asian; Some other race
48. Black or African American; American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander; Some other race
49. Black or African American; Asian; Native Hawaiian and Other Pacific Islander; Some other race
50. American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander; Some other race
51. White; Black or African American; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander
52. White; Black or African American; American Indian and Alaska Native; Asian; Some other race
53. White; Black or African American; American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander; Some other race
54. White; Black or African American; Asian; Native Hawaiian and Other Pacific Islander; Some other race
55. White; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander; Some other race
56. Black or African American; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander; Some other race
57. White; Black or African American; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander; Some other race

Given the many possible ways of displaying data on two or more races, data products will provide varying levels of detail. The most common presentation shows a single line indicating "Two or more races." Some data products provide totals of all 57 possible combinations of two or more races, as well as subtotals of people reporting a specific number of races, such as people reporting two races, people reporting three races, and so on.

In other presentations on race, data are shown for the total number of people who reported one of the six categories alone or in combination with one or more other race categories. For example, the category, "Asian alone or in combination with one or more other races" includes people who reported Asian alone and people who reported Asian in combination with White, Black or African American, Native Hawaiian and Other Pacific Islander, and Some other race. This number, therefore, represents the maximum number of people who reported as Asian in the question on race. When this data presentation is used, the individual race categories will add to more than the total population because people may be included in more than one category.