Sometimes group interviews are used in conjunction with one-to-one interviews. For example, after individual interviews, key ideas may be brought to a group for feedback.
Andrea Pheasey (2002) used small group interviews to explore what adult literacy students "think what being literate is." Andrea used small group interviews because:
I found the participants were more likely to elaborate on a theme when questions or comments were made by their fellows in the group.... The interviews became more conversational than simply a question/answer exercise. (p. 8)
Paula Davies (2006) used a group interview approach to collect students' responses to the use of personal narratives in an English class. She asked the students to form small groups and discuss and make notes on what they liked about the class, what they did not like and suggestions for improvement (p. 18).
The Saskatchewan Literacy Network (Ham, 2006), conducted focus groups with adult learners in order to
acquire information from as many learners as possible in order to set the direction of support groups in each community. (p. 5)
In Toronto, researchers used a combined focus group/interview approach to collect data from 56 adult learners:
We used a semi-structured interview approach to elicit answers to our basic question: "How do learners perceive progress." (Lefebvre et al., 2006, p. 5)
A questionnaire is similar to a structured interview. In both cases, the questions are predetermined. Questionnaires can include questions that require the participant to compose the response (similar to a structured interview), questions that include responses to choose from, or both.
Given the same number of participants, a questionnaire usually requires less time to collect data than doing interviews. For this reason, questionnaires might be used when you want to collect information from a large number of people.