Here is some more information about the limitations of measuring race with the current questions in the United States Census:

When the 2010 census asked people to classify themselves by race, more than 21.7 million — at least 1 in 14 — went beyond the standard labels and wrote in such terms as “Arab,” ”Haitian,” ”Mexican” and “multiracial.”

The unpublished data, the broadest tally to date of such write-in responses, are a sign of a diversifying America that’s wrestling with changing notions of race…

“It’s a continual problem to measure such a personal concept using a check box,” said Carolyn Liebler, a sociology professor at the University of Minnesota who specializes in demography, identity and race. “The world is changing, and more people today feel free to identify themselves however they want — whether it’s black-white, biracial, Scottish-Nigerian or American. It can create challenges whenever a set of people feel the boxes don’t fit them.”

In an interview, Census Bureau officials said they have been looking at ways to improve responses to the race question based on focus group discussions during the 2010 census. The research, some of which is scheduled to be released later this year, examines whether to include new write-in lines for whites and blacks who wish to specify ancestry or nationality; whether to drop use of the word “Negro” from the census form as antiquated; and whether to possibly treat Hispanics as a mutually exclusive group to the four main race categories.

This highlights some of the issues of social science research:

1. Social science categories change as people’s own understanding of the terms changes. Keeping up with these understandings can be difficult and there is always a lag. For example, a sizable group of respondents in the 2010 Census didn’t like the categories but the problem can’t be fixed until a future Census.

2. Adding write-in options or more questions means that the Census becomes longer, requiring more time to take and analyze. With all of the Census forms that are returned, this is no small matter.

3. Comparing results of repeated surveys like the Census can become quite difficult when the definitions change.

4. The Census is going to change things based on focus groups? I assume they will also test permutations of the questions and possible categories in smaller-scale surveys before settling on what they will do.