Though automated telephone systems can reduce some of these costs, many people resent the idea of being interviewed by a machine. Additionally, respondents can be cut off if they hesitate or misunderstand how to respond and important details to lengthy questions may be forgotten by the time a response is appropriate. If your survey project has strict time limitations, telephone surveys may work better than mail surveys. The validity of a survey's results depends upon how representative your sample is to the overall population. Choosing between mail and telephone surveys may depend on the database you have available and the type of customers you serve.
Telephone surveys can be advantageous if potential respondents needs to be qualified.
Random digit dialing can be useful for overcoming the problem of unlisted numbers or recently changed numbers. If an accurate data base is available, mail surveys can be more cost effective. They can also allow you to target specific customer groups each survey administration. Although in the past response rates have been 3 to 15 percentage points higher for telephone surveys than mail surveys, the difference has declined over the past decade. Mail surveys are often more suitable for respondents who are difficult to reach, due to busy schedules.