Overseers of the 2010 census said on Wednesday that it is almost impossible to determine the total cost of the decennial count.
"At this point, it's just unknown" if the cost of the census will ultimately surpass the current estimate of $14.7 billion, Commerce Department Inspector General Todd Zinser told the Senate Homeland Security and Governmental Affairs Federal Financial Management Subcommittee, which oversees the count.
A GAO report released at the subcommittee's hearing showed that the first major operation conducted by census workers -- the "address canvassing" campaign to confirm millions of addresses nationwide -- went $88 million over budget, or 25 percent of costs.
"We deserve tighter controls or better estimates, one of the two," said Sen. John McCain, R-Ariz., ranking member of the panel.
Once expected to cost $11.5 billion, estimates of the funds required to conduct the count jumped last year after a failed effort to equip census workers with handheld computers.
Census Director Robert Groves, who took the reins of the bureau in July, acknowledged last month that the agency is revising its methods of cost modeling.
At the hearing, Census officials pointed to several factors that make the final cost difficult to predict.
A low rate of response to the mailed census would mean higher costs, for example, because more census workers would have to be dispatched to retrieve the forms in person.
Officials noted flaws in the bureau's process for fingerprinting its temporary workers as part of their criminal background checks.
Robert Goldenkoff, director of strategic issues at GAO, told senators that as many as 200 workers who participated in the address canvassing effort may have committed crimes. Adequate background checks would have prevented their hiring, he said.