Semi-structured interview
A semi-structured interview is a research method most often used in the social sciences. While a structured interview has a rigorous set of questions that do not allow deviation, a semi-structured interview is open, allowing new ideas to emerge in response to the interviewee's input. The interviewer in a semi-structured interview generally has a framework of themes to be explored.
Semi-structured interviews are widely used in qualitative research; for example, in household research, such as couple interviews. A semi-structured interview involving, for example, two spouses can result in "the production of rich data, including observational data." There is no universally applicable sample size for interviews.