Some households haven't received any 2010 Census form. Others have duplicates.

It's no mistake. Most residents of urban neighborhoods have gotten two forms - part of the U.S. Census Bureau's effort to increase response rates in so-called "hard-to-count" census tracts.

"We want to make people aware that if you live in one of those tracts and you've already sent a form in, you'll still be getting another one," said George Conner, manager of the Cincinnati Central Office of the Census Bureau.

Conner's office is responsible for 79 census tracts, mostly in Cincinnati city neighborhoods. Of those, 75 should have gotten the duplicate forms. The Cincinnati Suburban office, responsible for Hamilton County suburbs and all of Butler and Warren counties, has 57 "hard-to-count" tracts getting another form.

While the additional mailing costs the Census Bureau $80 million to $90 million, officials say it could boost mailback rates by as much as 10 percentage points. That could save taxpayers millions, because it costs an average of $57 to send a census worker to each household that hasn't mailed back the form.

Households that have already returned a form can disregard the second mailing. The Census Bureau said it has controls to make sure only one form per household gets counted.