Data based on administrative records (individual income tax returns) from the Internal Revenue Service's Individual Master File (IMF) system, which includes a record for every Form 1040, 1040A, and 1040EZ filed with the IRS. The records included in this study were returns that were filed between January 1, 2009 and December 31, 2009. Generally, these are Tax Year 2008 returns although a limited number of late-filed returns for tax years before 2008 were also filed during this period. If a taxpayer filed returns for multiple years during this period, only the most recent return was included.