What is a panel? How is it used in marketing research? What disadvantages are associated with panels?

A panel is a sample of consumers or stores from which researchers take a series of measurements. Unlike a focus group, members of a panel are members over long periods of time. The information gathered from panels is used to tell marketing researchers if consumers change their behavior over time. A disadvantage is that the research firm needs to recruit new members continually to replace those who drop out. The new recruits must match the characteristics of those they replace to keep the panel representative of the marketplace.