One of the interviewer's duties is to ensure that you get reliable answers. For this it is necessary that the interviewer understands the interviewee, asks them through in a good way and processes the answers correctly. The extent to which the interviewer fails to do so is called interviewer bias.
Bias relates to disruptions and therefore it is a shortcoming in the way the interviewer acts. By the way, almost no one will do well 100 percent; there will always be a slight degree of disruption. Asking the question slightly differently will provoke a slightly different answer for the interviewee.
Interviewer bias can also occur during telephone surveys. The surveyor cannot read certain answer alternatives, or he can note the wrong answer from the respondent. A better term in this case is surveyor bias.
To prevent bias, a protocol must be drawn up and this must be strictly followed by the interviewer. This also prevents different interviewers from conducting the conversation in different ways. If not every interviewer achieves the same result with the same person, this is called interviewer bias. With properly instructed and well trained iterviewers this can be prevented.
Interviewer bias is difficult to investigate because people are not willing to be interviewed twice by two or more people on the same subject. Moreover, the opinion of the person may also change, so that the results will turn out differently with each interview. You can read more about that under the term reliability.