New census estimates don't match Utah's school enrollment figures, and local economists say the discrepancy backs up their claims that the federal government has been undercounting Utah's annual population figures.

Utah's school enrollment numbers increased by 34,743 between 2000 and 2005, from 475,269 to 510,012. But, estimates released today by the U.S. Census Bureau show a school-age population at 507,425, a loss of 1,895 people age 5 to 17 since 2000.

The difference between school enrollment and the July 1, 2005, census estimates for age, sex, race and Hispanic origin isn't surprising to Pam Perlich, a senior economist at the University's Bureau of Economic and Business Research and a member of the Utah Population Estimates Committee, which has long suspected annual census estimates undercount Utah's population.

Perlich pointed to actual birth certificates as more evidence of a census under-estimation, across the board. The census estimated there were 48,391 children younger than one year old in 2005, while there were 50,431 births in the state. Plus Utah has seen a net immigration over those years, she said.

"Unless they are leaking out of the state, the (census estimates) are too small for the youth and too small for the little babies."

School enrollment data also provide solid evidence of such an under count because enrollment figures are an actual count of students, while the latest census numbers are an estimate, said Robert Spendlove, manager of demographic and economic analysis for the Governor's Office of Planning and Budget.

The Census Bureau's 10-year census is accurate, the economists said, but the annual estimates released in between each census are suspect.

The difference between the actual counts and the estimates indicates "there could be a problem" in the methodology. Utah County and some cities successfully challenged their census estimates last year, boosting their 2004 populations, and there are also challenges this year. He said the census method tends to underestimate young and rapidly growing populations.

States can't challenge the estimates, but successful county challenges raise the overall state population, Spendlove said.

While there may be discrepancies with the numbers, Spendlove said many of the estimates overall trends hold true.

"Utah continues to have the youngest population in the nation, and our median age is the lowest in the nation," he said. "Our share under age 18 is the highest in the nation, and our share of the population under 5 is the highest."

Perlich said the Beehive State is seeing "echo booms" of the post-World War II Baby Boom.

"We're now having our biggest generation," Perlich said. "We've had record births for eight of the last nine years, and some of those kids are already showing up in the school system."