In addition to prison populations, the data also contain general population counts and estimates based on decennial census. Because general population figures are present, users can calculate imprisonment rates. Rates computed from the data will differ from previously published rates because they reflect final prison population counts and final general population estimates. Users should note that the data preserve what was reported in the historical record, and no attempts have been made to correct errors in the record. Also, some states are missing data for particular years; these absences are identified by missing data codes.