The statement about the Census Bureau about the "race" categories it is required by federal regulation to ask about says in full

"The U.S. Census Bureau collects race data in accordance with guidelines provided by the U.S. Office of Management and Budget (OMB), and these data are based on self-identification. The racial categories included in the census questionnaire generally reflect a social definition of race recognized in this country and not an attempt to define race biologically, anthropologically, or genetically. In addition, it is recognized that the categories of the race item include racial and national origin or sociocultural groups. People may choose to report more than one race to indicate their racial mixture, such as 'American Indian' and 'White.' People who identify their origin as Hispanic, Latino, or Spanish may be of any race."

http://quickfacts.census.gov/qfd/meta/long_RHI525211.htm

A similar statement is found as footnote 7 in the Census Brief 2010 "Overview of Race and Hispanic Origin: 2010"

http://www.census.gov/prod/cen2010/briefs/c2010br-02.pdf

which reads

"The race categories included in the census questionnaire generally reflect a social definition of race recognized in this country and are not an attempt to define race biologically, anthropologically, or genetically. In addition, it is recognized that the categories of the race question include race and national origin or sociocultural groups."

An earlier statement by the Census Bureau for reports on the year 2000 census

http://quickfacts.census.gov/qfd/meta/long_RHI625200.htm

says, "The concept of race as used by the Census Bureau reflects self-identification by people according to the race or races with which they most closely identify. These categories are sociopolitical constructs and should not be interpreted as being scientific or anthropological in nature. Furthermore, the race categories include both racial and national-origin groups.

"The racial classifications used by the Census Bureau adhere to the October 30,1997, Federal Register Notice entitled,"Revisions to the Standards for the Classification of Federal Data on Race and Ethnicity" issued by the Office of Management and Budget (OMB)."

In other words, the professional demographers who work on the United States Census claim only to be following the law, not to be practicing biological, anthropological, or genetic science when they ask for self-identification of "race." That claim has continued through two different presidential administrations as the bureau conducted two successive decennial censuses and numerous community surveys. The Census Bureau practice is based on are based on regulations from the Office of Management and Budget (OMB), which were announced on 30 October 1997

http://www.whitehouse.gov/omb/fedreg_1997standards

to take effect no later than 1 January 2003 for data collection by all federal agencies. The summary of comments on the 1997 regulations makes clear that not all Americans are united in regarding the current set of categories (which has changed several times in my lifetime) is meaningful. The distinct differences between the categories used in the United States and those used in any other country in the world should make clear that categories are indeed "sociopolitical constructs and should not be interpreted as being scientific or anthropological in nature." I bring this up because several recent threads here on Hacker News have interpreted "race" categories as if they have genetic or anthropological meaning, which they do not.

The long story about how to think carefully about race and ethnicity in the human population can be found in the books recommended for first reading in a Wikipedia user bibliography "Anthropology, human biology, and race citations bibliography"

http://en.wikipedia.org/wiki/User:WeijiBaikeBianji/Anthropol...

in Wikipedia user space.