A group of individuals selected to provide their opinions and/or track their purchasing behavior on a regular, ongoing basis. Panelists selected are representative of a target group or total population and provide personal and household information (such as demographics) to serve as sample selection criteria for individual research studies. Panelists often take inventory of the brands, products or services they purchase using handheld and mobile scanners, and record key information about their purchases such as price, quantity and location purchased.