Opinion polls can be wrong—just look at Thomas Dewey in 1948 or even Barack Obama, who led Hillary Clinton before the New Hampshire primary but lost anyway. Reuters outlines some factors that could be skewing current results:
- Turnout: Polls filter the results of phone surveys through models of who is likely to actually vote. But with turnout, especially among African-Americans, expected to set a record, “likely voter” models could be out of date.
- Cell phones: Pollsters reach households by phone, and with increasing numbers of Americans using cell phones and not land lines, a portion of the electorate is beyond their reach.
- The “Bradley Effect”: Though the widely cited theory that racist voters lie to pollsters has been questioned, those with strong racial prejudice may be left out of polls because they are more likely to hang up on telephone survey operators.