Advantages/Disadvantages - Questionnaires

Questionnaires - by post, telephone or email
Advantages - Reduces the personal influence of the researcher, Produces quantitative, reliable and representative data.
Disadvantages - Response rate may be low, Answers may be incomplete, Data may not be valid, Cannot be sure who completed the questionnaire, Limits possible answers the participant can give.

Structured interviews - face to face or by telephone
Advantages - Higher response rate, Can 'probe' the participant's responses by asking follow-up questions, Can assess truthfulness of participant
Disadvantages - 'Interview effect', Time-consuming so may get fewer responses, Limits possible answers the participant can give

Unstructured interviews - face to face or by telephone
Advantages - Can create rapport with participant, Can follow up responses in depth, Produces valid qualitative data
Disadvantages - Personal bias of interviewer, Data may be less reliable, Time-consuming