What BISG means
Bayesian Improved Surname Geocoding combines surname distributions with geography to estimate broad race and ethnicity probabilities. The method is common in political science, voting rights, public health, and disparity research when individual-level race or ethnicity is not directly observed.
For campaign work, the useful output is not a hard label. It is an explainable signal that can help teams plan language access, field coverage, persuasion universes, and community-specific outreach with more care than surname matching alone.
- Probabilistic scoring rather than a personal identity claim
- Surname signal from public Census surname tabulations
- Geographic priors when reliable local demographic data is available
- Thresholds that campaigns can review before using a segment
How CA Voter uses the signal
The product is built around a surname-plus-geography approach: surname race and ethnicity percentages are joined to a voter record, local demographic priors are applied when available, and the output is normalized into comparable percentage scores.
Unknown surnames and missing geography are handled conservatively. A voter can still appear in normal voter-file filters, but the modeled ethnicity score should not be treated as certain when the underlying data is thin.
Responsible campaign use
BISG is most useful when it improves outreach quality: bilingual planning, volunteer assignment, local message testing, and resource allocation. It should not be used as a substitute for self-reported identity, local knowledge, or compliance review.
CA Voter keeps methodology language visible because modeled demographic signals are sensitive. Campaigns should understand what the score means before building a voter universe around it.
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Questions
Does BISG identify a voter's ethnicity?
No. BISG produces probabilities from surname and geography signals. It should be treated as an outreach planning estimate, not as self-reported identity.
Why use BISG instead of surname matching only?
Surname matching ignores local context. BISG can combine surname information with geography, which usually gives campaigns a more useful and transparent planning signal.