Fact check: How does the US estimate the number of undocumented immigrants?

1. Summary of the results

The US employs multiple methodologies to estimate the number of undocumented immigrants, primarily relying on statistical analysis rather than direct counting. The Migration Policy Institute (MPI) uses an updated methodology that combines administrative data with the U.S. Census Bureau's American Community Survey (ACS) to calculate unauthorized immigrant populations ^[1]. This approach involves subtracting the number of legal immigrants from the total foreign-born population in the ACS, while adjusting for undercount issues, particularly among new entrants ^[2].

Pew Research Center employs a similar "residual method" that estimates the total immigrant population, determines the number of legal immigrants, and subtracts the latter from the former to arrive at unauthorized numbers ^[3]. Both organizations make adjustments to account for undercounts in censuses and surveys, recognizing that undocumented populations are often missed in official data collection.

Additionally, the Trump administration implemented data-sharing agreements that provide ICE with access to Medicaid enrollee information, including names, addresses, birth dates, ethnic and racial information, and Social Security numbers of nearly 79 million people ^{[4] [5]}. This represents a tracking mechanism rather than an estimation method.

2. Missing context/alternative viewpoints

The original question fails to address several critical aspects of undocumented immigrant estimation:

• Methodological limitations: The analyses reveal that both major research organizations acknowledge significant challenges with undercounting, particularly among recent arrivals and populations that avoid official surveys ^{[2] [3]}.
• Inclusion of protected populations: MPI's methodology includes individuals with temporary legal protection, such as DACA or Temporary Protected Status recipients, in their unauthorized population estimates ^[2], which may inflate numbers depending on one's definition of "undocumented."
• Government surveillance capabilities: The question overlooks the federal government's use of administrative databases like Medicaid records for immigration enforcement purposes ^{[4] [5]}, which represents a different approach from statistical estimation.
• Political implications: Immigration advocacy organizations would benefit from lower estimates to reduce public concern, while immigration restriction groups would benefit from higher estimates to justify enforcement measures. Research organizations like MPI and Pew Research Center maintain their credibility through methodological transparency, though their funding sources and institutional perspectives may influence their approaches.

3. Potential misinformation/bias in the original statement

The original question appears neutral and factual, seeking information about estimation methodologies rather than making claims. However, it implicitly assumes a single, standardized method exists when the reality is more complex. The question doesn't acknowledge that:

• Different organizations use varying methodologies that can produce different results
• The term "undocumented" itself can be interpreted differently (some include temporary protected status holders, others don't)
• Estimation methods have inherent limitations and uncertainties that affect accuracy
• The federal government uses both statistical estimation and direct data collection/surveillance methods for different purposes

The framing suggests a purely academic or statistical exercise when immigration estimation has significant political and policy implications that influence how different organizations approach and present their methodologies.