This prior agreement usually results in high response rates. In addition, mail panel surveys can be used for longitudinal research. That is, the same people can be questioned several times over an extended period. This enables the researcher to observe changes in panel members’ responses over time.
The major drawback to mail panels is that members are often not representative of the target population at large. For example, individuals who agree to be on a panel may have a special interest in the topic or may simply have a lot of time available.