What are the major disadvantages of focus groups and mailed surveys as compared to interviewing techniques such as “think aloud”?

What will be an ideal response?

The biggest disadvantage is that focus groups and mailed surveys do not give an interviewer adequate insight into users in the context of their work environment. It may be possible to understand some of the “what” of the user’s job, but very little of the “why” and “how” will be uncovered by a focus group or a survey.
Many people who would be forthcoming with their opinion in a one-on-one situation would be less willing to do so in a public meeting. The “think aloud” technique provides a one-on-one situation that the focus group does not.
Surveys typically have a very low return rate.