Well in research projects, structured interviews might be something that the interviewees cannot alter, such as a survey with multiple choice or Likert scale questions. These are usually referred to as quantitative methods. A semi-structured interview still might be formal in that the questions are the same for every participant, but they can answer in their own words. They are open questions and often referred to as qualitative methods. I assume you are asking in the sense of business or job interviews? If so, the same thing goes. Although in that environment, a structured interview can still have open questions, but the questions are the same for every participant. Once you diverge from that and ask different question to different candidates, this becomes semi-structured. Most job interviews are semi-structured, because even though there may be a list of questions for the interviewer to ask, the answer of the interviewee may alter the way the next question is worded or a new question altogether. Saving Changes...
When I worked in public sector for a provincial agency, we were required to use a structured interview process which involved developing and using a consistent set of questions, defining who and how many folks would be involved in the interview cycle and developing a scoring system for consistently evaluating candidates. On the other hand, most of my private sector jobs where I was either a hiring manager or a candidate were semi-structured where there were some pre-defined questions and overall flow but there was sufficient flexibility for ad hoc questions.
