Southern California planners and demographers are questioning census data on the region's commuting patterns released last week -- a concern that hints at broader problems with some census estimates.
The numbers released Thursday counted residents by where they live and work to measure commuting patterns. They were derived from data collected in the 2000 census long form, an extensive questionnaire filled out by about one of every six households in the country.
The data indicated a continuing and dramatic decrease in the number of people commuting to Los Angeles from surrounding counties -- an erosion of Los Angeles' decades-long standing as the region's economic heart.
While the trend toward increased economic independence in Orange, Riverside, San Bernardino and Ventura counties is unquestioned, census estimates of employment levels and commuter patterns conflict sharply with established jobs surveys and regional transportation studies.
The question confronting demographers now is, if census conclusions about Southern California employment and commuter patterns are wrong, what other census conclusions are off kilter?
"If that's wrong, then you have to question" all the long-form conclusions, said Hasan Ikhrata, director of planning and policy for the Southern California Assn. of Governments.
The problem appears to be rooted in a possible undercount of people with jobs.
The census found a 6% decrease in the number of employed people living in Los Angeles County over the decade ending in April 2000, while state labor statistics showed a 2% increase.
The census estimated 3.8 million Los Angeles County residents were working in April 2000, while the state counted 4.37 million.
A similar discrepancy existed for Orange County.
The census found a 3% increase in the number of residents with jobs, while state labor statistics showed an 8% increase.
Planners see another red flag in the census estimate of how many Riverside County residents work in Orange County. The census estimated that the number of commuters had increased by fewer than 2,000 since 1990 -- far below other estimates, such as a SCAG analysis that put the number at 5,000.
"No matter how you look at it, it's whacked," said Christopher Thornberg of UCLA's Anderson School of Management.
Census officials said they had found no statistical errors to explain the discrepancies, but that similar questions have been raised in Miami, in an unspecified New Jersey county and in the Bronx, in New York.
"It's disconcerting," said Phillip Salopek, a demographer in the Census Bureau's population division.
Although there's no indication of systemic problems with the data, he said, "We'd like to reconcile it so that we know exactly what's going on."
The census estimates are extrapolated from totals on the long-form surveys. Los Angeles, Miami and the Bronx are all home to relatively large numbers of immigrants -- both legal and illegal -- and Salopek said census officials would consider whether the discrepancies could have arisen from undocumented workers' reluctance to answer questions posed by a government official.
What effect the discrepancies might have is unclear. While the federal government relies on census figures to calculate aid to local governments under various programs, most transportation policy decisions are based on regional and local traffic studies, officials said.
"The census data is a snapshot that's accurate at the national level," said Kia Mortazavi, manager of planning and programming for the Orange County Transportation Authority. "It gives you some general trends, but for local planning, we do more specific origin-destination studies. We combine that with information from the state, local agencies, cities and traffic studies."
Ikhrata pointed out that some of the increase in traffic between Riverside and Orange counties, particularly on the Riverside Freeway, is from trucks and other non-commuter vehicles that would not show up in the census estimates.
"All you need to do is drive the freeway off-peak and on weekends," Ikhrata said. "The 91 Freeway is more congested on Saturday than any other day of the week, which tells me it's not really commuter trips but overall trips" that have increased crowding on the road.
But whether the increase in traffic is 2,000, 5,000 or more, no one can deny that congestion on the Riverside Freeway is a problem that must be addressed, Ikhrata said.
"The forecast for the next 10 to 15 years is that things are going to be worse," he said.