For the most part, those I've listed as personal references haven't been called. Usually if they call those, it's often for a job where there's a security clearance or if you're going to be working with confidential information such as Social Security numbers or medical records. Sometimes they do call previous employers, mostly to verify that you've worked for them. Usually, employers have you take a drug test, and run a criminal background check.
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"I do not feel obliged to believe that the same God who has endowed us with sense, reason,
and intellect has intended us to forgo their use."
- Galileo Galilei