Research has shown that individual interviews are the most effective means for getting feedback. Interviews can yield valuable insights that may have been overlooked in a formal survey. They often can be done without the intense preparation the must go into a survey assessment. Feedback is immediate. The customer sample is often much smaller than that of a survey.
Interviews are more intrusive for the respondent.
Interviewers will have to watch voice inflection and body gestures to avoid sending auditory or physical clues about the significance of an issue, or about the preferred response. Recording responses can provide accuracy of recall, however the customer being interviewed must grant permission. Results can then be analyzed both quantitatively and qualitatively. The parties involved have only auditory clues to react to questions. Respondents may tire of answering questions over the phone, especially if notes are being taken.