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Your voter registration is public record.

They build this sample data by compiling huge swaths of public records and buying private data.

Your political affiliation is not the worst of it, they can have the school your child goes to, the grocery store you visit, anything.

The worst really isn't the violation of privacy, it's the propaganda.

Most of the time the surveys themselves were meant to push information, the questions and answers were usually loaded.

Source: worked as a CATI technician, typist, and interviewer for a survey company in college.