Interviews are usually categorised into three groups: structured, semi-structured and unstructured interviews. This division is based on how the questions are posed. Each type has its purposes and uses, as well as its unique limitations.
A structured interview, or standardised interview, is conducted by asking all interviewees the same set of questions throughout the research project. In structured interviews, the interviewees are given a fixed set of possible answers and they must choose the option that most closely resembles their own opinion.
The questions are always asked in the same order so that all interviewees interpret the questions the same way. However, if the interview situation is not controlled, it is possible for the interviewees to answer the questions in an order that differs from the one intended by the researcher.
Having a predetermined set of possible answers limits the diversity of qualitative analysis. Analysing structured interviews is often closer to quantitative than qualitative research because of the lack of open answers.
A fully structured interview is a great method for well-defined research topics where having a limited set of possible answers is only a benefit. However, you should always consider whether actual physical survey forms would be better suited for the purpose of the project than an orally conducted structured interview.
In a semi-structured interview, the questions are formulated beforehand and all interviewees are asked the same questions, but there are no fixed answers to choose from. A semi-structured interview is more open than a structured interview, but it still has a clearly defined structure. It is a well-suited research method for topics that have not yet been extensively studied.
Focused interview is an example of an applied semi-structured interview and it is one of the most frequently used interview types. This interview format enables versatile interaction between the interviewer and the interviewee.
The themes of a focused interview are defined beforehand, but there is no strict order in which these themes are presented. In a focused interview, the set of questions serves mostly as a malleable reminder for the interviewer that gives way when the situation calls for it. All selected themes are covered with each interviewee, but the way the different themes are handled and to what extent can vary from interview to interview. Preparing a focused interview requires a lot of background research and the interviewees must be carefully selected so that the interviews will serve the goals of the research.
In an unstructured interview, the interaction situation very closely resembles free-form discussion. The interview delves into a theme relating to the research goals, but it can consist of only one question. Typical uses for these kinds of interviews include research projects that focus on biographical themes and narratives.
There is reason to remember that even in an unstructured interview, the research goals are still there. Despite the free form of the discussion, the interviewer must steer the flow of conversation towards the research goals when necessary.
An unstructured interview is also sometimes called an in-depth interview, as the purpose of the interview is to uncover the meanings related to the topic at hand as deeply and extensively as possible. The purpose of the interview is to understand the meanings people assign to their own experiences from multiple viewpoints.
You should always schedule a lot of time for these kinds of interviews so that the interviewee has enough time to think about the theme in depth. You might even need to conduct more than one interview. However, one must never assume that the interviewee tells the interviewer everything that would be of interest to the researchers about any topic.