Questionnaires are used for reaching:
- a large number of people, since the forms can just be handed out
- a widely despersed group of pople, as they can simply be posted out
Self-completion questionnaires are also les time consuming for researchers than interviewing, as they do not require the resercher to go and talk to the people face to face.
Anomoynous questionnaires are also v. useful if the researcher was to ask embarrassing questions about sensitive tpics such as sexual activites or illegal acts…