Microdata files are those that contain information on individuals rather than aggregate data . The U.S. Census Bureau's "Summary Tape Files" contain aggregate data and consist of totals of individuals with various specified attributes in a particular geographic area. They are, in a sense, tables of totals. The Bureau's PUMS (Public Use Microdata Sample) files, however, contain the data from the original census survey instrument with certain information removed to protect the confidentiality of the respondent. mid-level network