Face-to-face interviews are the most costly in terms of time and money. However, the interviewers can explain complex issues and explore unanticipated responses. Consider the question ``Do you have any suggestions for university administrators about how to improve the college experience of WMU students?" A response like ``Improve dormitory facilities'' may be too vague. The interviewer can then explore the issue further "Do you mean better rooms, better study facilities, more computers, better food?" Another advantage is the interviewers' ability to personally observe the respondent/s and the surrounding environment. This is particularly useful for, say, surveys about work conditions or workplace interaction.
Phone interviews are cheaper and quicker than face-to-face interviews. They also allow the interviewer to explain questions and react to responses. However, personal observation is not possible. Furthermore some respondents may feel that the survey call, like a telemarketer's call, is an invasion of personal time. This would inhibit honest, thoughtful answers.
Written questionnaire is the cheapest way to reach a lot of people. It also allows respondents to remain anonymous, probably the questionnaire's strongest advantage. However, response rate may be low ("another dumb survey") and this can lead to biased results. Furthermore, poorly constructed questions can lead to inaccurate results.
Table 2.1 breaks each of the 3 categories above into smaller categories, and lists the primary advantages and disadvantages. Feel free to add more categories.