A "don't know" option does not appear to reduce uninformed responses without reducing the overall response rate or the response rate for questions about which the respondents have information.

Question

Quizplus · Accepted Answer

Including a "don't know" option can actually help in reducing uninformed responses by allowing respondents who genuinely do not know the answer to a question to opt out, rather than forcing them to provide a potentially inaccurate answer. This can improve the quality of the data collected without necessarily reducing the overall response rate or the response rate for questions about which respondents are informed.

A "Don't Know" Option Does Not Appear to Reduce Uninformed