To understand Census data on language trends and their implications, it's essential to understand how the information was gathered:

1. These numbers are based entirely on "self-reports" – respondents' own subjective assessments of their language usage and proficiency. Follow-up studies in this area have shown that self-reports tend to be unreliable.

2. Census questions about language are abbreviated, ambiguous, and – for many people – confusing (see below). No explanatory notes or objective criteria are provided to help respondents in answering them. So they yield less accurate information than more careful surveys do, according to critics (e.g., Veltman, 1988).

3. Perhaps the best to be said for these questions is that the Census has asked them consistently since 1980, rather than changing their focus every ten years, as in the past. So it is possible to plot trends for the past two decades – 1980-1990 and 1990-2000 – without having to juggle apples and oranges.

4. Census data about language are estimates based on the "long form" questionnaire sent to a sample of about 20 million (one in six) U.S. households in 2000. Detailed results from this survey are scheduled to be released by early 2003.

5. Preliminary results were announced in August 2001 from the Census 2000 Supplementary Survey of about 700,000 households. These figures offer a preview of the full Census findings but are no doubt even less precise.

6. Here are the questions the Census asks about language in the U.S.A.:

a. Does this person speak a language other than
English at home? 

Yes or No [If No, skip to the next question. If Yes]:

b. What is this language?
(For example: Korean, Italian, Spanish, Vietnamese)

[and]

c. How well does this person speak English?

Very well
Well
Not well
Not at all

• How often do I need to speak another language to answer "Yes"? Every day? Once a month? What if I speak only English except when my mother is visiting?
• How proficient must I be in this non-English language? Fully fluent? Able to get by? Just learning?
• What if I continue to speak my first language frequently but not at home, because I live alone or have no family member who speaks the language? 

8. The net effect of these ambiguities is almost certainly to overstate the U.S. language minority population as it is commonly understood: persons who maintain fluency in a native language other than English. A substantial number of respondents from native-English-speaking backgrounds seem to be reporting the use of other languages. In the 1980 Census, for example, 28 percent of those who said they spoke Spanish at home also reported non-Hispanic ethnicity – hardly a credible finding, considering how few Anglo-Americans are fluent bilinguals.

9. Self-reports of English-speaking ability are equally dubious. In the early 1980s the U.S. Department of Education, working with the Census Bureau conducted resesarch to determine how language-minority parents' ratings of their children's English correlated with objective measures:

• The Children's English and Services Study (O'Malley, 1981) reported that 59 percent of children (aged 5-14) who were rated as speaking English "well or very well" were in fact limited-English-proficient. 
• The English Language Proficiency Study, released in 1982, concluded that "speaks English very well" is a reliable proxy for fluency in the language – if not for assessing individual needs, then at least for counting the population (McArthur, 1993). 

10. On the other hand, the Census has acknowledged that it substantially undercounts immigrants and Native Americans. This problem obviously tends to depress its estimate of linguistic diversity. In 1990, for example, it failed to record speakers of more than 50 Native North American languages that were still spoken at the time.

McArthur, E.K. 1993. Language Characteristics and Schooling in the United States, A Changing Picture: 1979 and 1989. Washington, DC: National Center for Education Statistics.

O'Malley, J.M. 1981. Children's English and Services Study: Language Minority Children with Limited English Proficiency in the United States. Rosslyn, VA: National Clearinghouse for Bilingual Education.

Veltman, C. 1988. The Future of the Spanish Language in the United States. Washington, DC: Hispanic Policy Development Project.