Number Verification

The verification of a telephone number in a telephone survey is done by an interviewer who confirms with a respondent that the number that was ostensibly dialed is in fact the number that was reached. The need to do this has been reduced over the years as more landline telephone surveys have come to be conducted with computer-assisted telephone interviewing (CATI) systems that include software and hardware to place the calls to the sampled telephone numbers, as opposed to having interviewers manually dial the numbers. However, the need for number verification has not been eliminated completely, as even with automatic dialing equipment mistakes sometimes occur. Furthermore, in the United States and due to current federal telecommunications regulations, all cell phone numbers that are sampled for a telephone survey must be hand-dialed—unless the cell phone owner has given the survey organization prior consent to be called—and thus interviewers will need to verify whether they have dialed the sampled number correctly.

There are several reasons that a landline (or cell phone) telephone survey may not reach the correct number, even when using equipment to place the calls. For example, national and local telephonic systems are subject to occasional error when “wires get crossed” (the electronic signals get mixed up), thus leading to a call reaching another number than the one to which it was intended. Call forwarding, whereby one telephone number is programmed by its owner to ring at another number, can also lead to the “wrong” number being reached. This is problematic when a business number that appears in an RDD sample is forwarded to a residential number. In this case, the household would not be eligible unless one of its residential numbers also was sampled. However, if a business number were reached because the residential number that was sampled in RDD was forwarded to it, then the resident reached via her or his forwarded home number would remain eligible. If the telephone survey has sampled “named persons,” then reaching them on a different number than what was dialed does not make them ineligible. In these instances of number verification, the interviewer will learn whether the number dialed is not the number reached, and if it is, then the interview may continue or may be politely terminated and coded as out-of-sample depending on the manner of forwarding that took place. Using manual dialing will lead to errors made by the interviewers who are placing the calls. Thus, whenever interviewers are hand-dialing sampled numbers, a verification that the correct number was reached always should be included in the introduction of the survey before the questionnaire is administered. Typically, this verification is done after cooperation has been gained, because it is assumed that doing it too soon after initial contact will lead to an increase in nonresponse.