Panel analysis

No one knows how many billions of items of panel data have been collected in the United States. It may well be that the number of such items collected each year runs into billions. By "panel data" is meant observations of behaviour - physical, oral, or written - of a set of individuals, families, households, stores, firms, or organizations at two or more points in time. Most of the data, and most of the attention here, refers to the individual person, but, mutatis mutandis, similar concepts and models can be used for the larger units of analysis.