Level of structuralization |
Structured interview |
Data are collected by asking closed questions in the order provided by highly specific interview guidelines |
Useful for asking questions without omitting any details that should be checked with each research participant |
Leaves little room for different interpretations of the participant’s responses or expressing original thoughts |
Semi-structured interview |
Between a structured and unstructured interview; interview guidelines are developed in advance, but the questions are not strictly set and may vary |
The most widely used data collection method in qualitative research, as it allows interviews to be conducted flexibly depending on the characteristics and responses of the participants |
Researcher bias may influence the interview process |
Unstructured interview |
The interview is conducted like a regular conversation, with extremely minimal prior information about the research topic and adherence to interview guidelines to exclude the intention for acquiring information needed for the research |
Can obtain rich and realistic meaning and experiences of the research participants |
The quality of information acquired and length (duration) of interview may vary depending on the competency of the interviewer, such as conversational skills and reasoning ability |
Sample size |
One-on-one in-depth interview |
Excluding cases in which a guardian must accompany the research participant, such elderly or frail patients and children, a single participant discusses the research topic with one to two researchers during each interview session |
This data collection method is recommended for research topics that are difficult to discuss with others and suitable for obtaining in-depth opinions and experiences from individual participants |
The range of information that can be acquired may vary depending on the conversational skills and interview experience of the interviewer and requires a relatively large amount of effort to collect sufficient data |
Focus group discussion |
At least 2 (generally 4–8) participants discuss the research topic during each interview session led by the researcher |
This method is effective when conducting interviews with participants who may be more willing to open up about themselves in a group setting than when alone, such as children and adolescents |
Richer experiences and opinions can be derived by promoting interaction within the group |
While it can be an effective data collection method, there may be some limitations in the depth of the interview; some participants may feel left out or not share their opinion if 1 or 2 participants dominate the discussion |
Interview method |
Face-to-face |
The interviewer personally meets with the research participant to conduct the interview |
It is relatively easy to build rapport between the research participant and interviewer; can respond properly to the interview process by identifying non-verbal messages |
Cannot conduct interviews with research participants who are difficult to meet face-to-face |
Non-face-to-face |
Interview between the interviewer and research participant is conducted through telephone, videoconferencing, or email |
Suitable data collection method for topics that deal with political or ethical matters or intimate personal issues; in particular, email interviews allow sufficient time for the research participant to think before responding |
It is not easy to generate interactions between the research participant and interviewer; in particular, it is difficult to obtain honest experiences through email interviews, and there is the possibility of misinterpreting the responses |