NEW YORK -- The number of U.S. children being raised by their grandparents rose sharply as the recession began, according to a new analysis of census data. The reasons, while somber, were not all economic.

These grandparents often give themselves high marks as caregivers, but many face distinctive stresses as they confront unanticipated financial burdens and culture shock that come with the responsibilities of child-raising.

In all, roughly 7 million U.S. children live in households that include at least one grandparent, according to a Pew Research Center analysis of the most recent Census Bureau data, from 2008. Of that number, 2.9 million were being raised primarily by their grandparents -- up 16 percent from 2000, with a 6 percent surge just from 2007 to 2008.

"Clearly something was going on" in those years, said Pew senior researcher Gretchen Livingston, a co-author of Thursday's analysis. "We don't have the data to explicitly state that this is related to recession, but it's a very educated guess."

Reasons for grandparents taking over child-rearing duties are manifold, often involving a single parent who becomes overwhelmed with financial problems, is incarcerated, succumbs to illness or substance abuse or dies. High rates of divorce and teen pregnancies fuel the phenomenon, as do long overseas deployments.

"It's almost inevitable that there is some stress around the reason these grandparents and grandchildren come together," said Donna Butts, executive director of the nonprofit advocacy group Generations United.

Overall, according to the Pew center, 34 percent of grandparent caregivers are unmarried and 62 percent are women.

The phenomenon of grandparents raising grandchildren has been proportionally higher among blacks and Hispanics than among whites, but the sharpest rise from 2007 to 2008 was among whites, with a 9 percent jump, according to Pew.

In all, 53 percent of the grandparent caregivers are white, 24 percent are black and 18 percent Hispanic.