Source: Public Policy Institute of California
A new report in which taxpayer records were used to estimate California’s undocumented immigrant population by county is interesting on a couple of counts. First, the report from the Public Policy Institute of California estimates that Los Angeles County is home to a little under one million undocumented immigrants, 9.3 percent of its population. Second, it provides a sense of how many undocumented immigrants file income tax returns.
The population count report accompanies a broader report from the institute on the state of illegal immigration today, as well as related political and public attitudes. But back to the methodology: Because it’s so difficult to get a good count of the undocumented population, the researchers used public records for Individual Taxpayer Identification Numbers, or ITINs, as a basis for the estimates.
ITINs have been used since 1996 by people without work authorization who do not have a valid Social Security number, but who want to file. The researchers used publicly available ITIN counts by ZIP code. According to the report, ITIN use has increased dramatically since 1996, with the Internal Revenue Service having issued more than 14 million ITINs by December 2008 (the year used for the report’s estimates).
Of course, no proxy used to count undocumented immigrants is perfect. Some don’t file tax returns, not all who file them use ITINs, and some of those who use ITINS are not undocumented. However, the report explains:
When we examine ITIN tax filers with U.S. filing addresses, we find that 90 percent in 2008 include wages. Only unauthorized workers would file tax returns with wages and an ITIN; authorized workers with wages would file tax returns using SSNs. Therefore, it is safe to conclude that the vast majority of ITIN filers are unauthorized workers.
A statistical model that weighed other factors was based on the ITIN counts; according to the report, ITIN data had not previously been used for estimating undocumented immigrants at the county and ZIP code level.
Based on these records, Los Angeles leads California counties in terms of sheer numbers. However, undocumented immigrants form a higher percentage of the population in less dense rural zones like Imperial, Monterey, San Benito and Santa Clara counties.
The report also features maps with undocumented population estimates by ZIP code of the entire state and of the Los Angeles and San Francisco Bay areas.
