TDI (Telephony Depth Interview)

It is a method of in-depth interview that is conducted over the phone instead of face-to-face.
This method like FGD and IDI, will provide a deep insight into the mentality of the target group. But the difference is that it will be conducted one-on-one and by telephone not face-to face, and each interview will last about an hour and to achieve this objective, the respondents should be given incentives.
In the marketing research, the telephone provides a relatively easy way to interface with consumers, linking people who might not otherwise be able to share their thoughts due to physical restraints. But it can also impede a researcher’s understanding of data by prohibiting him or her from capturing critical non-verbal cues that can manifest during face-to-face interviews. The aforementioned insulation and isolation of people (and, in this case, consumers) make meaningful relationships hard to foster. The only challenge of this method is the not so strong communication and commonalities during the interview, but at the same time, it has the advantages of in-depth face-to-face interviews, such as the following:
Interviewers have greater opportunity to ask follow-up questions, probe for additional information, and circle back to key questions later on in the interview to generate a rich understanding of attitudes, perceptions, motivations, etc.
There is a higher quality of sampling compared to some other data collection methods.

•Researchers need fewer participants to glean useful and relevant insights.

•There are none of the potential distractions or peer-pressure dynamics that can sometimes emerge in focus groups.

•Because in-depth interviews can potentially be so insightful, it is possible to identify highly valuable findings quickly.

Common uses for IDIs include branding research, customer satisfaction, market need, Obstacles and market problems, new product and service interest, consumer/customer, as well as others. Results from IDIs point organizations in the right direction and give critical feedback for their next move.