More than 80% of the public polls used to track key indicators of U.S. public opinion, such as the President’s approval rating or support for Democratic presidential candidates, are conducted using online opt-in polling. A new study by Pew Research Center finds that online polls conducted with widely-used opt-in sources contain small but measurable shares of bogus respondents (about 4% to 7%, depending on the source). Critically, these bogus respondents are not just answering at random, but rather they tend to select positive answer choices – introducing a small, systematic bias into estimates like presidential approval. CONT.
Pew Research Center
