A trained interviewer collects and codes the data directly. The major advantage is the trust that the interviewer builds with the respondent. Visual aids can also be shown to help the respondent respond. The main disadvantage is high cost and time. Another disadvantage is that since the interviewer is present, the respondent might be discouraged to give honest answers.
Telephone interviews are the most popular method of observation using structured surveys.
An advantage is that the interviews can be conducted back to back, saving time. Since the respondents are anonymous, sometimes the interviewer can obtain answers to sensitive questions. A disadvantage is the restricted type of questions that can be asked due to no visual aids and limitation of choices. A major disadvantage is refusals and early termination of the interview. The surveys are handed directly to the respondent and filled out.