A non-sampling error resulting from a mistake made either consciously or nonconsciously by an interviewer (see “Interviewer”) during the interview which can lead to inaccurate data. This type of error can be attributed to several factors, including but not limited to, interviewer bias (see “Interviewer Bias”), interviewer cheating (see “Interviewer Cheating”), incorrect reading of questions, incorrect recording of responses or behavior that influences participants’ responses in some way. Also referred to as “Interviewer Effect” or “Interviewer Variance.”