DANBURY -- As residents send back their decennial 2010 U.S. Census forms, some will receive a second census form in the mail. This is not a duplicate, but a different survey altogether: the American Community Survey.

The American Community Survey measures social and economic information every year rather than once a decade.

In 2000, one in six households received a 40-page form with 53 questions during the census count. In 2010, all households received a short form, with 10 questions that included the residents' names, gender, age, race, ethnicity, etc.

The American Community Survey replaces the former long-form questionnaire.

At the start of every month, the questionnaire is mailed to a scientifically selected sample of households in counties throughout the nation, according to the U.S. Census Bureau. Once a household receives the questionnaire, it will not receive it again for another five years.

The questionnaire is not an official population count, but rather a way to view trends.

Responding to the American Community Survey is required by law, according to the Connecticut Better Business Bureau.

The American Community Survey has been administered since 2005. The U.S. Census Bureau mails out 250,000 forms a year.

"The ACS gets a 95 percent response rate," said Arthur Bakis, information services specialist at the Boston Regional Census Center.