The use of the telephone has been found to be one of the most inexpensive, quick and efficient ways of surveying respondents. The ubiquity of telephone ownership as well as the use of unlisted numbers are factors that must, however, be considered as part of the sampling frame, even in North America, where the number of households with phones approaches 100%. Telephone surveys also allow for random sampling, allowing for the extrapolation of characteristics from the sample to the population as a whole.
There tends to be less interviewer bias than in interview surveys, especially if the interviewers are trained and supervised to ensure consistent interview administration. The absence of face-to-face contact can also be an advantage since respondents may be somewhat more inclined to provide sensitive information. Further, some people are reluctant to be approached by strangers, whether at their home or in a more public location, which can be overcome by the more impersonal use of the telephone.
On the other hand, telephone surveys are also known to have a number of limitations. The length of the survey has to be kept relatively short to less than 15 minutes as longer interviews can result in refusal to participate or premature termination of the call. The questions themselves must also be kept quite short and the response options simple, since there can be no visual aids such as a cue card.
The increasing use of voice mail and answering machines has made phone surveys more difficult and more costly to undertake. Calls that go answered, receive a busy signal or reach a machine, require callbacks. Usually, eligible respondents will be contacted a pre-determined number of times, before they are abandoned in favour of someone else. The potential for response bias must be considered, however, when discussing the results of a study that relied on the telephone.
The sample for a telephone survey can be chosen by selecting respondents
- from the telephone directory, e.g. by calling every 100th name
- through random-digit dialling (RDD) where the last four digits of a telephone number are chosen randomly for each telephone exchange or prefix (i.e. first three numbers), or
- the use of a table of random numbers.
Two practices that are increasing in popularity and that raise considerable ethical issues, since the respondents are misled into believing that they are participating in research, are:
- the survey sell (also known as sugging), whereby products or services are sold, and
- the raising of funds for charity (also knows as frogging).