A panel is a periodic study conducted for various companies. Unlike omnibus surveys, respondents and questions are exactly the same from one survey to the next (there is a small renewal rate).
The concept of « panel » originates on a fixed sample of individuals interviewed ; as a consequence we call panel the procedure of a study done on a panel of consumers. In France, companies specialized in panel studies represent about 42% of the activity on the field of studies and research.
In the recruitment phase the panel must be sure on the collaboration of respondents. There are different advantages to panel studies, for example, the ability to observe evolution of attitudes and behavior of the same individuals. Evolution is more difficult to interpret on ad hoc studies (risk of mistakes related to sampling). On the other hand, panel has theoretical limits. The sample is supposed stay the same, which is impossible (some consumers leave the panel because of lassitude). In practice a panel is periodically renewed. Finally, there is a risk of panel bias, meaning that panelist rationalize their purchasing behavior and become less representative because they are used to be questioned about their purchase behavior.