- When the questionnaire is short (up to 10 minutes), it may take more time to travel from one respondent to another. Telephone interviews are more efficient.
- When the type of respondent are geographically dispersed, it may also take more time to travel from one respondent to another.
- The respondent may be very mobile or finds it inconvenient to make an appointment that lasts only 10 minutes. The same matter would be resolved faster over the phone.
- Since telephone interviews are usually conducted from a central location, under supervision, it is easier to control the quality of the interviews.
Telephone surveys are less personal. When the survey entails sensitive issues, this is always a reason try to decrease the respondent's possible discomfort. to For that reason, it is desirable, whenever possible, to inform respondents that they will be contacted and to give some background of the purpose of the survey. Read also my post What to expect from a telephone interview.